B GIO DC V O TO TRNG I HC S PHM H NI ..

CNG CHUYN

A L PHN B C

Ngi son: NCS. T Th Thy

2

H NI - 2011

3 MC LC Trang Phn I. I CNG V A L PHN B NG VT......................................4 1.1. Mt s khi nim c bn................................................................................4 1.1.1. a l sinh vt..........................................................................................4 1.1.2. a ng vt............................................................................................4 1.1.3. Vng phn b..........................................................................................4 1.1.4. S pht tn..............................................................................................7 1.1.5. Trung tm pht tn..................................................................................8 1.1.6. Tr ngi v chng ngi i vi pht tn ng vt.................................8 1.1.7. S cch li.................................................................................................8 1.2. Cc vng a l ng vt...............................................................................10 Phn II. A L PHN B C...............................................................................12 2.1. Mt s yu t chnh nh hng n s phn b c.......................................12 2.1.1. Nhit .................................................................................................12 2.1.2. Nng oxy ha tan trong nc...........................................................12 2.1.3. mn (Salinity k hiu S)...................................................................12 2.1.4. pH v kim loi nng........................................................................13 2.1.5. Tc dng chy..................................................................................13 2.1.6. Cc chng ngi vt..............................................................................14 2.2. a l phn b c bin trn th gii...............................................................16 2.2.1. Phn vng a l phn b c sng ven b (littoral)................................18 2.2.1.1. Vng Bc cc.................................................................................19 2.2.1.2. Vng n i Bc bn cu...............................................................19 2.2.1.3. Vng nhit i...............................................................................20 2.2.1.4. Vng n i Nam cc....................................................................20 2.2.2. Phn vng a l c sng bin su.......................................................21 2.2.3. Phn b a l c bin khi i dng..................................................21 2.3. a l phn b c nc ngt trn th gii......................................................23 2.3.1. c trng c bn...................................................................................23 2.3.2. Phn vng a l phn b c nc ngt..................................................25 2.3.2.1. Khu h c vng Ton Bc (Holartic)..............................................25

4 2.3.2.2. Khu h c vng n - Trung Hoa..............................................27 2.3.2.3. Khu h c nc ngt vng chu Phi (Ethiopian)............................27 2.3.2.4. Khu h c nc ngt vng Tn nhit i - Nam M (Neotropical) 28 2.3.2.5. Khu h c nc ngt vng chu c (Australian)...........................28 2.4. Lch s t nhin, a l phn b c bin v c nc ngt Vit Nam..........28 2.4.1. Lch s t nhin ca Vit Nam..............................................................28 2.4.1.1. Giai on tin k Cambri................................................................28 2.4.1.2. Giai on c kin to.....................................................................29 2.4.1.3. Giai on tn kin to....................................................................30 2.4.2. Lin h gia cc con sng c Vit Nam vi cc con sng c N......31 2.4.3. Mt s nt chnh v iu kin t nhin ca Vit Nam...........................32 2.4.3.1. V tr a l......................................................................................32 2.4.3.2. Sng ngi.......................................................................................34 2.4.3.3. Cc m h t nhin v h cha....................................................35 2.4.3.4. Cc ao rung..................................................................................36 2.4.4. V tr a l ng vt hc ca Vit Nam.................................................36 2.4.5. a l phn b c bin Vit Nam...........................................................37 2.4.6. a l phn b c nc ngt Vit Nam..................................................40 2.4.6.1. Thnh phn loi c nc ngt........................................................40 2.4.6.2. c tnh v quan h a l ng vt ca khu h c nc ngt........40 TI LIU THAM KHO.......................................................................................48

5 Phn I. I CNG V A L PHN B NG VT 1.1 Mt s khi nim c bn 1.1.1 a l sinh vt a l sinh vt (Biogeography) l khoa hc nghin cu v thm thc vt v s phn b ca qun th ng vt cc min ca Tri t; l khoa hc v nhng quy lut phn b v mi quan h gia cc loi thc vt, ng vt hnh thnh thm thc vt v qun th ng vt [8]. 1.1.2 a ng vt a ng vt l khoa hc nghin cu v s phn b ca ng vt v cc quy lut chung ca s phn b y [12]. 1.1.3. Sinh quyn Sinh quyn (Biosphere) l mt trong nhng quyn ca Tri tm trong ton b cc sinh vt sinh sng. Sinh quyn bao gm: kh quyn hay cn gi l tng i lu; thy quyn v thch quyn [8]. 1.1.4 Vng phn b Mi loi sinh vt phn b mt khu vc xc nh c gi l vng phn b. Vng phn b l mt vng lnh th hay khng gian ca v Tri t trong loi hay nhm loi ng vt chim c. Vng phn b ca loi l lnh th c cc c th ca loi sinh sng. Vng phn b ca ging l lnh th c cc c th ca cc loi thuc ging sinh sngtng t nh vy vi cc vng phn b ca h, b, lp. Nh vy khi nng bc phn loi ln cng cao th lnh th ca vng phn b ca bc phn loi cng rng (tr mt s trng hp c bit). V d: vng phn b ca c Vy tay (Latimeria chalumnae) hin nay cng trng vi vng phn b ca ging c Vy tay (Latimeria) [8], [17]. Vng phn b sinh vt khng i khi nng bc phn loi c gi l vng phn b di lu (relic area). Vng phn b ca loi l c s cho cc hc thuyt v vng phn b sinh vt. - Vng phn b thc: l vng phn b thc t m loi sinh sng, ti c nhng iu kin sinh thi thun li cho s sinh tn pht trin ca loi. - Vng phn b m rng: ngoi vng phn b thc c lnh th c iu kin sinh thi thch hp cho s sinh tn ca loi. Xc nh c vng phn b m rng c ngha thc tin ln trong vic phng tr cc loi gy hi.

6 - Vng phn b t nhin: Cc loi sinh vt hnh thnh, pht trin v chim c mt vng lnh th ni chng c th tm c iu kin sng thch hp. Lnh th chng chim c nh vy l vng phn b t nhin. - Vng phn b nhn to: vng phn b ca sinh vt do s tc ng ca nhng hot ng ca con ngi l vng phn b nhn to. - Hnh thi vng phn b: bt c loi ng vt no khi mi hnh thnh ch chim c mt vng phn b nh. iu kin sng thun li loi sinh trng v gia tng s lng, vng phn b c m rng dn. Vng phn b ca loi c m rng ra pha c iu kin sng thun li, pha no c iu kin sng khng thun li cho loi, ranh gii vng phn b ni khng c m rng, thm ch cn b thu hp li, hnh dng vng phn b v th rt khc nhau. ng thi trong t nhin iu kin sinh thi phn b rt khng ng u, hnh thi vng phn b khng c hnh th nht nh. Cc hnh thi ch yu ca vng phn b: lin tc, vng, b chc thng, hnh mng li [8]. - S phn b ca loi trong vng phn b: s phn b ca sinh vt theo hai cch thc chnh: phn b u v phn b khng u (phn b ngu nhin v phn b tp trung theo nhm). Nguyn nhn nh hng n s phn b ca loi: iu kin sng trong ranh gii vng phn b v gii hn sinh thi ca loi. S phn b ca loi trong khu phn b c th l lin tc hay ri rc hoc tn mn. S phn b l lin tc khi iu kin sng ca loi trn khu phn b l u, ng nht, kh nng sinh tn ca loi trn ton khu phn b l t thay i (loi sng bin). Cn nhng khu phn c iu kin sng thay i, mi ni mt khc th s phn b c th ni ny u, ni kia li ri rc...Trong t nhin, phn b u rt t gp. Trong mt s trng hp phn b u phn nh kt qu cnh tranh mnh lit gia cc c th trong qun th. V d: S phn b u ca cc c th c ui c (Macropodus epercularis) phn nh kt qu cnh tranh mnh lit gia cc c th trong qun th. - Vng phn b cch bit: l vng phn b, gm hai hay nhiu phn ring bit cch bit nhau bi khong khng gian rng ln hay do chng ngi ngn cch m cc c th ca loi trong cc khu ring bit vi iu kin sinh thi hin ti khng th khc phc chng ngi sang vng phn b khc. V d: ging c Coregonus hin ti sng cc h ng Bc Irland, Ty Nam Ecosse v Ty Bc ca Anh. Ging c ny c 3 loi gn nhau: 1 loi Irland, 2 loi Ecosse v Anh. Ngy xa, ging c ny ch c 1 loi. Khi , c Ty Bc chu u cao

7 hn mt i dng so vi v tr by gi. Ti Irland c mt ci h trong thung lng su, ging c ny sng h . Do t lin tt xung, nc bin trn vo h, c theo ngc dng sng i vo cc h cho n ngy nay. Cc h cch bit nhau, nn t mt loi c khi ngun phn lm 3 loi c lp ngy nay sng cc h Irland, Ecosse v Anh. Rt c th sau ny 3 loi c tr thnh 3 ging khc khau [8]. - Vng phn b cch bit i dng: vng phn b ca cc ng vt bin cng c s cch bit. C th phn ra 3 dng phn b cch bit trong i dng: phn b Lng Bc (Amphiboreal), phn b Lng B v phn b Lng Cc (Bereonotal) hay phn b Cc Bc - Cc Nam. + Phn b Lng Bc (Amphiboreal): nhiu loi ng vt phn b khu vc Bc Thi bnh dng v Bc i ty dng nhng khng c cc vng bin Bc cc. V d: c Bn (Pleuronectiformes) v cc loi c trong h c Tuyt Bc i ty dng c 46 loi, cn Bc Thi bnh dng c 12 loi ging nhau; c Trch (Clupeidae) phn b Lng Bc [8]. + Phn b Lng Cc (Bereonotal): l dng phn b cch bit ca ng vt phn cc Bc v cc Nam ca Tri t. Phn b Lng Cc ph bin cc dng ng vt bin a lnh, tc l cc dng sng Bc cc v Nam cc, c cc dng a lnh km hn, tc cc dng phng Bc v phng Nam, vng bin nhit i v nc m khng c cc dng ng vt ny. V d: nhiu loi c thuc h Scopelidae, h c Trch (Clupeidae), c Sacdin, c Mp (Selachoidei) c trng cho kiu phn b Lng Cc [8]. - S thay i ca loi trong vng phn b: iu kin sng trong vng phn b c th thay i theo thi gian. V th, hng nm thng c s thay i ch ca loi trong vng phn b. S thay i din ra c tnh chu k. Thay i ch theo chiu nm ngang thng thy nhiu loi c di c theo ma tm ni . V d: c Hi thuc h Salmonidae t i dng vo cc con sng vt thc , c Chnh sng chu u (Anguilla anguilla) di c t cc con sng ra i dng vi khong cch ti hng nghn kilmet [8]. 1.1.5 S pht tn Pht tn l kh nng khc phc iu kin kh khn m rng vng phn b. ng vt c hai kh nng pht tn: pht tn ch ng v pht tn b ng. Pht tn ch ng l kh nng ca ng vt pht tn do t chuyn vn. Pht tn b ng l kh nng

8 ca ng vt khc phc nhng tr ngi pht tn nh iu kin bn ngoi nh nh gi, dng nc, ng vt, ngi... mang i [8], [17]. Kh nng khc phc kh khn m rng vng phn b hoc chuyn ti vng phn b mi ca c gi l kh nng pht tn ca c. Kh nng pht tn ph thuc vo nhiu yu t, thng th loi c gii hn sinh thi rng thng c vng phn b rng hn so vi loi c gii hn sinh thi hp. Song kh nng sinh tn ch l mt phn ca kh nng pht tn. S pht tn cn ph thuc vo kh nng di chuyn ca c, phng thc sinh sn v nhiu yu t khc. V d: c R ng (Anabas testudineus), c Lc (Channa striata) c c quan h hp ph trn mang, hoa kh, c kh nng di chuyn bng vy trn cc on ng xa hng trm mt khi tri ma, chng c kh nng di chuyn trn cn trong iu kin ph hp di chuyn t thy vc ny sang thy vc khc, vng phn b ca c R ng v c Lc rt rng, c c ghi nhn c tt c cc quc gia ng Nam , Trung Quc, n ... S pht tn ca c nc ngt c th din ra theo cc con ng sau: - Pht tn ch ng: nhiu loi c c kh nng pht tn ch ng nh c R ng (Anabas testudineus), c Lc (Channa striata), c Thi li (Periophthalmodon schlosseri), cc loi c thuc ging c Tr (Clarias)...S pht tn ch ng ca c c th din ra theo cc cch sau: + S di chuyn ch ng. + Di chuyn trong qu trnh lch s; + Di chuyn theo ma; + Di chuyn ngy m. - Pht tn b ng: Hu ht cc nhm c u c kh nng pht tn b ng cc mc khc nhau. Kh nng pht tn thay i trong qu trnh pht trin c th ca loi. C mt s cch chnh sau: + Dng chy ln nh hi lu trong i dng hoc dng nc trong ma l cc con sng. Dng hi lu c th a u trng c di chuyn xa ti hng ngn km, sc mnh ca ca cc con l cng c th a c sng ti cc khe sui di chuyn i xa. + ng vt: trng c bm vo ng vt thy sinh, sau bm vo chn chim, th nh m c th di chuyn xa. Loi c Pungitius platygaster c pht tn t lu vc bin Aral ti Ty Xiberi thuc trng hp ny (G.V. Nikolski).

9 + Ngi: s thun ha di nhp cc loi c nui phc v cho nhu cu thc phm v gii tr gp phn m rng vng phn b ca nhiu loi c, c R phi sng Nil nhp vo Vit Nam c tn gi l c R phi vn (Oreochromis niloticus) l mt v d in hnh. Loi c ny sau khi c nhp vo nc ta thch nghi vi iu kin sng nn phn b rng khp cc lu vc nc ngt t Bc vo Nam. Nhiu loi c khc cng m rng vng phn b theo cch . Khi nhp c ging nhiu khi ngi ta a lun c u trng ca cc loi c khng mong mun vo khu h, s xut hin c Mng trong cc ao nui c sng Hng do ng dn vt c bt ng thi vt lun c c Mng con, c Sc bm (Trichogaster trichopterus) vn rt ph bin cc thy vc nc ngt Nam B nhng n xut hin hu ht cc lu vc nc ngt trong c nc. 1.1.6 Trung tm pht tn Mt vng c coi l trung tm pht tn l mt vng m dng nguyn thy no , trong mt thi gian a cht nht nh, pht tn ra ngoi v hnh thnh nhng dng mi. Nhng vng phn b ca nhng loi gn nhau u lin h cht ch vi nhau th hin s tin ha ca loi [8]. 1.1.7 Tr ngi v chng ngi i vi pht tn ng vt - Tr ngi l nhng cn tr s pht tn nhng ng vt vn c th vt qua c. - Chng ngi l nhng cn tr s pht tn m ng vt khng th vt qua c. Gm: 1. Chng ngi vt l nh mi trng cn i vi ng vt nc v mi trng nc i vi ng vt cn. 2. Chng ngi kh hu nh: nhit , m, ma tuyt, t m hay ngp nc, chiu sng... 3. Chng ngi sinh hc nh thiu thc n thch hp, bnh tt, cnh tranh sinh hc, k th. 1.1.8 S cch li Nhng chng ngi trong thin nhin c th dn n chng qun ring bit ca loi cch li vi khu h ng vt. Cch li lu di s dn n s tin ha ca ng vt. Mc sai khc ca cc dng sng trn vng phn b cch li so vi dng gc l do cc yu t nh: kh nng di c ca loi th hin mc no; khong thi gian c cch li lu hay mi; tnh cht c xa phn cch ca cc vng trn Tri t. Cch li v

10 lnh th dn n cc dng cch li a l. Cch li a l a n hnh thnh cc phn loi. Vng phn b ca hai phn loi c th tip gip nhau. T cch li a l c th dn n cch li sinh thi. Trn th gii c mt s h lc a c hnh thnh t lu vi nhng loi c lu i cho n nay vn gi c nhng iu kin sng nh xa nh h Baican Bc chu , h Orchrida bn o Bancan, h Tanganyika chu Phi, h Poxo Celebes. Cc h ny c hnh thnh vo u k t. iu kin sng cc h t thay i cho n ngy nay. C y do cch li nn c nhiu loi c xa v a phng. Trong cc hang ng su, iu kin sinh thi rt c bit: lun lun ti, khng kh t, nhit khng kh v nc khng thay i v thp hn nhit ngoi hang. Vi c im sinh thi nh vy, hot ng ca c trong hang c nhng c trng ring nh khng th hin tnh chu k, sinh sn quanh nm, sinh trng u, dinh dng c ngy ln m, sc t da km pht trin thng c mu trng hay hi hng, hi vng, c quan th gic km pht trin c khi b m, thc n l nhng b hu c nh xc ng vt, phn di. C trong hang ng thng ngho v thnh phn loi v s lng c th, thiu cc nhm phn loi cao. C trong hang ng, nht l hang ng su, thng b cch li vi bn ngoi nn c th tm thy nhiu nhm c xa b tuyt dit t lu trn mt t, nhiu dng a phng, nhiu loi c ngun gc t nhng loi ngoi hang. V d: loi c m Ambliopis speleus sng trong hang ln Mamautova nc M l h hng gn gi vi loi c bnh thng Chlorogaster sng ngoi ao h [8], [17]. B nc ngm nm su trong lng t, th cha c nhng nghin cu c th v s phn b ca c, cn nhng b nc ngm trong cc hang ng c nghin cu k hn. Ngi ta pht hin thy c khong 15 loi c thuc 6 h. Cc loi c sng b nc nm su trong y hang, phn ln bt ngun t cc loi c nc ngt trn mt t, mt phn nh bt ngun t t tin bin, mt s loi c khc th cha r ngun gc, mt s khc th bt ngun t dng c xa b tuyt dit. C phn b o v c bn tun theo quy lut ca khu h c trn lc a. Tuy vy, do cch li v iu kin sng o khc vi t lin nn khu h c o c nhng c im ring ca n. o c th ln hoc nh, gn hay xa b lc a, b cch li vi xung quanh bi nc bin, gm c o lc a v o i dng. C o chu nh hng ca c lc a ln cn v nhng c im pht ca n. C sng o thng ngho v thnh phn loi, kch thc th b hn so vi c sng trong t lin [8], [17].

11 1.2 Cc vng a l ng vt Ngi ta chia cc vng a l ng vt thnh hai loi: cc vng a l ng vt trn lc a v cc vng a l ng vt i dng, c trnh by bng 1. Bng 1. Cc vng a l ng vt trn lc a v i dng [8]CC VNG A L NG VT Vng C Bc (Palearctic) (u--Bc Phi) Vng Tn Bc (Nearctic) (Bc M) Vng n Trung Hoa (ng Phng - Oriental) C a CC VNG A L NG VT TRN LC A Vng chu Phi (Ethiopian) 1. Phn vng Bc cc (Arctic) 2. Phn vng Canada 3. Phn vng Xonocxki 4. Phn vng chu u - Xiberi 5. Phn vng a trung hi 6. Phn vng Trung 7. Phn vng Trung Quc - Mn Chu 1. Phn vng n 2. Phn vng ng Dng (Indochinese) 3. Phn vng Malayxia (Sundaie) 4. Phn vng Celebes (Wallacean) 1. Phn vng Ty Phi 2. Phn vng ng Phi 3. Phn vng Nam Phi 4. Phn vng Madagasca 1. Phn vng Trung M 2. Phn vng ng n (Antiles) 3. Phn vng Guyan - Brazin 4. Phn vng Patagonie Vng chu c Nam a Vng chu c (Australian) Vng Polinezi Vng New Zealand 1. Phn vng c chnh thc 2. Phn vng New Ghine 3. Phn vng New Zealand 4. Phn vng Polinezi 5. Phn vng Hawai

Bc a (c vng Ton Bc) (Holartic)

Tn a

Vng Tn nhit i Nam M (Neotropical)

1. Vng nc lnh pha Bc hay vng Bc cc (Arctic) 2. Vng nc n ha Bc Thi bnh dng (Boreo-Pacific) CC VNG A L NG VT I DNG 3. Vng nc n ha Bc i ty dng (Boreo-Atlantic) 4. Vng nc m n dng - Thi bnh dng 5. Vng nc m i ty dng hay vng nhit i i ty dng 6. Vng nc lnh pha Nam hay vng Nam cc (Angtarctic)

Vic phn chia cc vng a l ng vt ni ring thng da vo cc yu t sau y: Yu t a hnh, a mo; yu t kh hu; mi trng sng; yu t phn b a l; tnh thch nghi ca n v loi; s phn b ca cc lp ng vt.

12

Hnh 1.1. Cc vng (min) a l ng vt trn lc a (theo P. Banarescu)

Hnh 1.2 Cc vng a l ng vt i dng (theo Bou v Chanton) 1 v 3 vng gn b; 2 v 4 vng ngoi khi; 1 v 2 min lnh; 3 v 4 min nng; a-a v b-b ranh gii ca nhng vng cc.

13 Phn II. A L PHN B C 2.1 Mt s yu t chnh nh hng n s phn b c 2.1.1. Nhit Nhit l yu t sinh thi c nh hng n s phn b, s tn ti v dit vong ca cc loi c, c nhng loi c ch phn b nhng vng ny m khng thy phn b cc vng khc. V d: c R phi (Oreochromis mossambicus) c gii hn sinh thi v nhit t 5oC - 42oC. Khong thun li cho cc chc nng sng cho loi c ny l t 20oC 30oC. Cn C Chp (Cyprinus rubrofuscus) c gii hn sinh thi v nhit t 2oC 44oC. Khong thun li cho cc chc nng sng cho loi c ny l t 18oC - 32oC [9]. 2.1.2. Nng oxy ha tan trong nc Nng oxy ha tan ho tan trong nc l yu t rt quan trng nh hng n s phn b ca cc loi c, nht l cc loi c nc ngt. Do vy, nhiu loi c ch sng c nhng ni sng, sui c nng oxy ha tan cao nh a s cc loi c thuc b c Chp (Cypriniformes). Ngc li c nhng loi c khng cn nng oxy ha tan cao nn chng sng c trong cc ao, h nc t ng nh cc loi c thuc h c Tr (Clariidae), h c Tra (Pangasiidae). S gia tng hm lng cht hu c trong nc dn n s gia tng nhanh chng ca vi sinh vt, l nguyn nhn c bn dn n s thiu ht hm lng oxy ha tan nhiu thy vc nc ngt, c bit l cc thy vc nc ngt gn thnh ph v cc khu dn c. Bin dao ng ca hm lng oxy cn ph thuc vo nhiu yu t khc c bit l su v din tch ca vc nc... 2.1.3 mn (Salinity k hiu S) Da vo mn, ngi ta chia ra lm 3 loi mi trng nc: nc ngt c (0 S 1 ); nc l (1 < S 32 ); nc mn S > 32 . mn l yu t quan trng c nh hng quyt nh n s phn b ca cc loi c nc ngt, nc l v nc bin (c bin). C nhng loi c ch sng c bin, ngc li c nhng loi c ch sng c nc ngt, nhng cng c nhng loi c va sng c mi trng nc ngt/nc mn va sng c mi trng nc l (vng ca sng gip vi bin). Mt s b c Vc (Perciformes), b c Trch (Clupeiformes), b c Bn (Pleuronectiformes), b c i (Mugiliformes), b c Chnh (Anguilliformes), b c

14 Km (Beloniformes), b c Nheo (Siluriformes), b c Nc (Tetraodontiformes) thng phn b vng nc l ca sng. C ca cc h ca sng ring bit khng tht a dng so vi vng bin k cn vi chng, vi s lng loi dao ng t 80 - 233 loi. Khu h c thuc ton vng ca sng dc b bin nc ta c tng hp li ln ti 615 loi nm trong 120 h ca 29 b c. y c ti 26 loi c Sn, cn li l c Xng [13]. 2.1.4 pH v kim loi nng pH ca nc cng ph thuc vo mc ha trn ca nc sng v nc bin. Nc bin c pH thng ln, t 8,1-8,4. Do s i mi nc vng ca sng v t l ha trn ca nc sng v nc bin m pH dao ng t 7,8-8,4. pH cao v n nh trong thi k ma kh v cng xa dn khi nh hng ca nc ngt. Mi trng nc ngt c pH thay i kh ln, c cc loi mi trng axit, trung tnh v baz. Chnh pH ca mi trng nc nh hng khng nh n s phn b ca cc loi c. a s cc loi c phn b mi trng nc c pH trung tnh. Mt s loi c c th c xem l c ch th cho mi trng nc chua phn l c Bi tru (Trichopsis vittata), c Thia ta (Betta taeniata), c Thia xim (Betta splendens), cc loi c thuc ging c Sc (Trichogaster). Cc kim loi nng c trong mi trng nc cng nh hng n s phn b ca cc loi c, nht l cc loi c nc ngt v nc l. 2.1.5 Tc dng chy Tc dng chy cng nh hng n s phn b ca cc loi c, c loi a nc chy nhanh nh cc loi c Vy bng thuc cc ging Vanmanenia, Glyptothorax..., c loi a nc lng nh cc loi thuc ging Monopterus, Misgurnus. Tc dng chy nh hng ti tnh cht nn y, nhng ni nc chy mnh, y tr si . Thng ngun sng sui c dng chy mnh, giu ng vt y, khng c ng vt ni, c th c c nhng bin i v mt cu to thch nghi vi dng nc chy nhanh nh cc loi c thuc h c Chch vy bng (Balitoridae), ging c Chin Oreoglanis... c thn dp theo hng lng bng, mt bng hoc ming hnh thnh c quan chuyn ha nh gic bm ngc, ming hoc ru, trn cc vy mt s c bin i c bit nh vy ngc hoc vy bng ni nhau, trn tia vy hnh thnh cc rnh bm ... Cn vng ca sng c ch dng chy phc tp, tn ti cc loi c vi cc c tnh sinh thi khc nhau.

15 2.1.6. Cc chng ngi vt Cc chng ngi vt l yu t nh hng n vng phn b m rng hoc thu hp ca nhiu loi c. Cc chng ngi vt c th l thc cao, cc di t, cc dng nc c nhit khc bit hoc nng mui, bin l chng ngi i vi c lc a v c o, c ca cc h thng sng khc nhau trong lc a hoc chng ngi do ngn dng chy ca cc con sng, sui lm h cha nc, lm p thy in... Vic ngn dng lm nh hng n kh nng di c ngc dng v quay tr li ca cc loi c. V d: cc loi c Vy bng thuc ging Vanmanenia, c Chin thuc ging Oreoglanis... vn sng cc thc nc chy xit, khi hnh thnh cc h cha (thy in, ti tiu) cc thc nc ny b mt, chng buc phi di chuyn ti v tr khc tn ti. Cc chng ngi theo kiu ny c th thay i theo thi gian v khng gian, chng hn vo ma l lu lng nc ln ca cc con sng thuc Bc B v Bc Trung B (Vit Nam) u vo vnh Bc B lm gim nng mui ti cc vng ca sng ph v s ngn cch gia cc h thng sng ti khu vc ny. Mt yu t sinh thi c th l chng ngi di c i vi loi ny nhng khng phi chng ngi i vi loi khc, dng chy mnh l chng ngi i vi cc loi c nh, bi li km nhng c th khng phi l chng ngi i vi c khe, bi gii. 2.2. a l phn b c bin trn th gii So vi trn lc a ni c rt nhiu chng ngi t nhin nh cc dy ni cao, nhng khu vc rng ln ngn cch cc lu vc sng, sa mc... lm cho cc khu vc c nc ngt b cch li, vng phn b ca cc loi c b thu hp, th i vi c bin, mi trng sng kh ng nht, cc chng ngi t nhin khng c nh hng quan trng. Nhng cng c nhng kh khn: 1. ng ranh gii gia cc min khng c r rang, ngoi ra phn bin su cha c nghin y c c s hon thin vic phn vng. 2. a s ng vt ni chung, c ni ring ngay c n bc phn loi khng cao c th c vng phn b rt rng. 3. Mi nhm c i dng c cch phn b rt khc nhau, do khng bit ly nhm no lm c s cho vic phn vng. Nghin cu phn b a l c bin cn ch cc im sau: - Gia ba vng sinh thi ca bin: vng ven b thm lc a (Littoral), vng bin khi i dng (Oceanic) v vng bin su (Deep sea), cc c trng phn b ca cc loi c khc nhau do cn nghin cu ring bit.

16 - Trong s nhng nguyn nhn vn thng c nu ra gii thch quy lut phn b ca c: v a l, sinh thi, lch s a cht, qu trnh pht sinh pht tn, lch s ca loi, i vi c bin th lch s a cht c ngha kh quan trng. V nhng yu t sinh thi th nhit (theo i), mui (xa lc a) l nhng yu t quan trng nh hng n s phn b c bin. - C 3 quy lut thng cp n khi ni ti phn b a l c bin: + Phn b lng cc, lng n i (bipolaire, bitemperes); + Phn b song n i, song nhit i (amphiboreale, amphitropicale); + Phn b hai b Thi bnh dng, hai b i ty dng (amphipacifique, amphiatlantique). Quy lut phn b lng cc, lng n i ni ti nhng loi c hoc nhng loi rt gn nhau phn b c hai cc, c hai vng n i ca cc bin m gia thuc nhit i th khng c. V d: cc cp loi c sau y c gi l phn b kiu ny: Sardina pilchardus Bc i ty dng - S. sagas Nam i ty dng. S. sagas Bc Thi bnh dng - S. melanosticta Nam Thi bnh dng. Engraulis japonicus Nht, Vin ng Lin x - E. antipodia c, Tn Ty lan. E. mordax Bc M - E. rigens Pru. E. enerasi Na uy - E. capens Nam chu Phi. Gii thch quy lut chi phi kiu ny L. S. Berg (1933) v Hubbs (1952) c kin ng n nht: trong thi k bng h Pleistocene nc vng nhit i lnh, nhiu loi c pha Bc v pha Nam lin lc tip xc vi nhau v sau ny ht thi k bng h, nhng loi c vng nhit i hoc b tiu dit hoc dn ln pha Bc hoc xung pha Nam. Quy lut phn b song n i, song nhit i ni ti nhng loi c phn b c n i Thi bnh dng v n i i ty dng hay nhit i Thi bnh dng v nhit i i ty dng. V d: Song n i Bc i ty dng Hippoglossus hippoglossus (L.) Clupea harengus harengus L. Ammodytes tobianus L. Mullotus villosus (Muller) Bc Thi bnh dng H. stenolepis Schmidt C. harrngus pallasi Val. A. permalus Gir. M. villosus (Muller)

17 Gii thch trng hp ny, L. S. Berg (1933) cho rng vo k Pliocne (trc bng h) hoc cui Pliocne (sau bng h) vng bin Bc cc m v vy c Bc Thi bnh dng pht tn sang Bc i ty dng. ng pht tn i dc Bc lc a chu, hoc dc Bc M. L. S. Berg cn c vo cc loi c ha thch thu thp c dc ng pht tn. V d: song nhit i. Cc loi thuc ging Etrumenus, Elops va phn b bin Nht Bn nhit i Thi bnh dng va phn b cc vng nhit i i ty dng. iu ny c gii thch nh nhng ha thch ca loi ny bt c vng chung quanh a trung hi hin nay, chng pht tn t vng nhit i n - Ty Thi bnh dng sang i ty dng theo b Tethys trong k Tam. Quy lut phn b hai b Thi bnh dng, hai b i ty dng ni ti nhng loi c sng ven b bin hai bn thuc Thi bnh dng v i ty dng. V d ca trng hp ny l Elops va phn b bin Nht bn, bin ng, va phn b b pha Ty Bc M California. Gii thch trng hp ny chc chn cc loi khng th vt c mt khong i dng rt rng ln ca Thi bnh dng m ch c th gii thch chng theo ng ven b bin ln pha Bc qua b Brinh sang b pha Ty Bc M lc m vng cc cn m. V vic phn vng a l phn b c bin v c trng khu h c bin ti cc vng n nay c rt nhiu cc cng trnh nghin cu: trong s ny cn nhc ti cc tc gi quan trng sau: Gnther (1880), Ortmann (1896), Ekman (1953), L. S. Berg (1933), Zenkenich (1952), Gurianova (1972). 2.2.1. Phn vng a l phn b c sng ven b (littoral) [19] c trng sinh thi hc ca vng ven b thm lc a l: iu kin sng tng i n nh; c nh sng; oxy thun li; mui thay i; sinh vt rt phong ph (thc vt - ng vt). V vy, i b phn cc loi c bin hin nay sng vng ven b ny. S phn vng a l c bin c coi l ng n nht l: vng Bc cc; vng n i Bc bn cu; vng nhit i; vng n i Nam cc; vng Nam cc.

18

Hnh 2.1. S phn vng a ng vt thm lc a ven binI. Bc cc; 1,2. Ranh gii pha Nam; II- n i Bc i ty dng; 3. Ranh gii pha Nam; III. n i Bc Thi bnh dng; 4. Ranh gii pha Nam; IV. Nhit i Trung M; 5. Ranh gii pha Bc; 6. Ranh gii pha Nam; V. Nhit i Ty Phi; 7. Ranh gii pha Bc; 8. Ranh gii pha Nam; VI. Nhit i i ty dng; 9. Ranh gii pha Bc; 10. Ranh gii pha Nam; VII. Nhit i Ty Thi bnh dng - n Dng; 11. Ranh gii pha Bc; 12. Ranh gii pha Nam.

2.2.1.1. Vng Bc cc c im chung ca vng ny l nhit thp, nc b bng bao ph, nng mui tng i thp do nhiu sng chy vo. Sinh vt ni chung ngho v thnh phn loi, phn b u trn mt tng y. Khu h c thuc vng ny gm mt s ging thuc bc cc in hnh Myoxocephalus, Gym-nelis. Licodes, Lumpenus, Aspidophoroides, Liopsetta, Boreogadus, Arctogadus, mt s ging thuc n i Eleginus, Mallotus. Thnh phn s lng c bin vng ny thp, bin Kara (61loi), bin Lap-chep (28 loi), Barent (113 loi), Bch hi (50 loi). 2.2.1.2. Vng n i Bc bn cu c im ca vng l nhit m hn Bc cc v thay i theo ma r nht l tng mt. Sinh vt rt giu c v c coi l trung tm khai thc qua trng (sn lng cng nh nng sut) nht trn th gii hin nay. Gia hai vng n i bc Thi

19 bnh dng v n i Bc i ty dng thnh phn loi c kh ging nhau. Tuy vy cng cn phn chng thnh hai phn vng. Thuc phn vng n i Bc i ty dng thnh phn khu h c th phn bit: - Dng Bc cc: Myoxocephalus, Liparis, Lumpenus, Hippoglossoides. - n i in hnh: Cottus, Zoarces, ammodytes, Scophthalmus, Limanda, Pleuronectes, Serbastes, Cyclopterus, Anarhichas, Pholis Hippoglossus, gadus, Melanogrammus, Clupea. Cc loi Clupea harengus, Gadus morhua, Melanogrammus aeglefinus, Scomber scomber, Salmo salar l nhng loi kinh t thuc b chu u. Cc loi Brevoortia pomolobus, Alosa... l nhng loi kinh t thuc vng b Bc M. - Cn nhit i: Sardina gii hn trong ng ng nhit 120 - 200C Gia hai vng b i ty dng thuc chu u v Bc M kh ging nhau. Thnh phn loi ca c bin thuc vng ny kh phong ph. Bin Phn Lan 69 loi, a trung hi khong 500 loi, Hc Hi v b Azov 175 loi, b Caspien 75 loi. Thuc phn vng n i Bc Thi bnh dng thnh phn khu h c bin phong ph hn phn vng n i Bc i ty dng. S loi c hu y cng nhiu hn cng c th phn bit phn vng ny thnh: Dng Bc cc c cc loi thuc Zoarcidae, Liparidae, Cottidae, Agonidae. Dng n i in hnh: Limanda, Pleuronectes, Lepidopsetta, Platichthys. Dng cn nhit i: Clupanodon, Sphyraena, Trichiurus, Clupea, Theragra. C mt s loi sai khc gia hai vng b chu v chu M. Bin Bring c 300 loi, bin Okhost c 240 loi, bin Nht Bn trn 600 loi. Bin Nht Bn c coi l mt trong nhng bin phong ph nht th gii. Do diu kin sng thun li nn cc loi pha Bc cng nh pha Nam xm nhp ti rt ng. 2.2.1.3. Vng nhit i c im ca vng ny l: nhit tng mt thng xuyn cao, thay i theo ma khng r v c s sai khc r tng mt v tng y. Sinh vt rt phong ph. Vng triu c nhiu bi s vt v rn san h. Gii hn ca vng ny trng vi ng ng nhit 200C. C th chia vng ny thnh bn phn vng: Phn vng n - Ty Thi bnh dng. Phn vng Ty chu Phi; Phn vng ng chu M; Phn vng Ty chu M.

20 - Phn vng n - Ty Thi bnh dng c coi l vng c thnh phn khu h c phong ph nht. Nhiu loi nguyn thy cn gi li c n nay cng v vy y c coi l trung tm pht sinh ca nhiu nhm c bin hin nay. Kh nhiu cc h c chuyn sng cc dng san h: Chaetodontidae, Pomacentridae, Labridae, Monacanthidae, Ostracionidae... cc bi s vt c h c chuyn ha Periophthalmidae. S lng cc loi c y kh nhiu: bin nam Nht Bn thng k c 1236 loi. Bin ng gn 1000 loi. ng ch c nhng c thuc phn vng ny khng pht tn c qua Thi bnh dng v ti b bin chu M. - Phn vng Ty chu Phi ni chung ngho nn, c mt vi loi c a trung hi. Phn vng ny khng c rn san h. S lin h gia khu h vi khu h n M Lai ch cn li vi loi c xa. C l nhng loi ny pht tn ti y qua a trung hi trong k Eocne. Khu h c hai b Ty chu Phi v ng chu M c lp vi nhau. Tnh cht ny th hin r khi ly cc loi thuc Pleuronectiformes lm v d. - Vng cn ng chu M v phn vng Ty chu M mang tnh cht kh c o. Trong qu trnh hnh thnh nhiu ln chng lin h vi nhau do eo t Panama lc ni lc chm. Hai phn vng ny ni chung c chng 56 loi. 2.2.1.4. Vng n i Nam cc c im chung ca vng ny kh ging vng n i Bc bn cu. Thnh phn ngho hn so vi n i Bc bn cu. y c mt s h c c hu nh: Bovichthyidae, Nothothenidae, Muraenolepidae, Galaxiidae, Gempylidae. Ngoi ra c nhiu loi hoc loi gn vi n phn b c Bc bn cu. Thuc vng n i Nam cc b Ty Nam M cn k n cc loi thuc vng Nam cc c c trng gn nh Bc cc nhit m quanh nm di 00C, nhiu tng bng rng ln. Thnh phn loi y phi k ti cc loi thuc h Notothenidae, Bathydraconidae, Chaenichthyidae, Zoarcidae, Liparidae. Khu h c Nam cc cng nh khu h n i Nam bn cu cha c nghin cu nhiu. 2.2.2. Phn vng a l c sng bin su [19] c xp vo c sng bin su l tt c c sng vng dc lc a v tng y cc bin su. c im chung ca vng ny l nh sng thiu, khng c thc vt y, sinh vt ngho, mi trng n nh, n iu, nhit thp 1- 20C, p sut ln. Cn phn bit cc loi c sng dc lc a, cc vng bin su v cc su.

21 Ni chung nghin cu khu h c cc vng bin su cha c nhiu. Tuy vy cng bit c mt s ging c sng y v c tnh sinh hc ca chng, c th k l: c Sn c Chiamydselachus, Centrophorus, Centroscyllium, c Ton u (Chimaera harriota), c Xng c cc h Synaphobrachidae, Derichthyidae, Halosauridae, notacanthidae, Lipogeniidae, Macruridae, Zoarcidae, Lophidae, Antennaridae, Ogcocephalidae, Lophiidae. Nhng loi c sng bin su phn b rng ri, v d nh loi Bathygadus longifilis gp gn nh khp cc bin su. i b phn c d ming rng. Hu ht c c quan pht quang, c quan th gic tiu gim, v hnh dng thn hoc di dp bn hoc trn. Ngun gc ca nhng loi sng bin su hin nay c gii thch l bt ngun t vng ven b dc lc a xung. l trng hp ca Cottunculus subspinosus pht sinh t C. microps, Raja hyperborea t R. radiata. V phn vng a l c sng bin su c th tham kho s ca Vinogradov (1959) (hnh 2.2).

Hnh 2.2. S phn vng a ng vt bin su (theo Vinogradov (1959)A Vng Thi bnh dng - Bc n dng; A-1 Phn vng Thi bnh dng; A-1a . Tnh Bc Thi bnh dng; A-1b. Tnh Ty Thi bnh dng; A-1c. Tnh ng Thi bnh dng; A-2 Phn vng Bc n dng; B Vng i ty dng; B-1- Phn vng Bc cc; B-2- Phn vng i ty dng; B-2a- Tnh Bc i ty dng; B-2b- Tnh Ty i ty dng; B-2c- Tnh ng i ty dng; C- Vng Nam cc;

22C-1- Phn vng Nam cc i ty dng; C-2a- Tnh n dng; C-2b- Tnh Thi bnh dng.

2.2.3. Phn b a l c bin khi i dng c im chung ca vng ny l: tng mt c nh sng, trong ln c sng v hi lu i dng, nng mui cao v n nh, sng trn mt lp nc rt dy. V sinh vt ch gm c sinh vt ni v sinh vt t du. S phn vng a ng vt c tng mt di dng th hin hnh 2.3. Khu h c bin khi i dng rt giu v nhiu loi c coi l i tng khai thc chnh hin nay ca ngh c bin th gii; thuc vng n i Thi bnh dng v i ty dng c th k cc loi v cc ging sau: Clupea harengus, Sardina, Engraulis, Scomber scomber, Sarda sarda, Xiphias gladius.

Hnh 2.3. S phn vng a ng vt c i dng tng mt (theo Vinogradov (1959)1. Bc cc; 2. Hn i; 3. n i; 4. Cn nhit i; 5. Nhit i; 6. Cn nhit i; 7. n i; 8. Hn i; 9. Nam cc

Thuc vng bin nhit i c th k Dactylopterus, Cypselurus, Scomber, Pelamys, Thynnus, Aixis, Scomberomorus, Istiophorus. Cng xung su, s lng loi cng t i. T tng nc su di 500 m mi thng k c khong 500 loi. Hin nay ngh c bin i dng mi khai thc c tng mt n su 100 - 200 m.

23 c trng thch nghi hnh thi ca cc loi c vng bin khi l bi li gii, mu xanh nh bc hoc tm. Nhng loi su hn c quan pht quang. Nhiu loi c tng mt i dng c s di c thng ng, ban m ni ln, ban ngy chm xung v di c ngang. 2.3. a l phn b c nc ngt trn th gii [8], [19] 2.3.1. c trng c bn Phn b cc thy vc ni a bao gm hai nhm c: c nc ngt in hnh v c chu c nng mui cao hn c nc ngt in hnh. Khng c c nc ngt in hnh phn b cc ni nh o Madagascar, qun o Antilles, chu c (tr loi c Phi) cc Nam chu M Tuy nhng ni ny cng c nhng thy vc nc ngt thc s v nhng ni ny tch khi cc cc lc a qu sm trc lc pht trin ca i a s cc c nc ngt hin nay. Trn th gii nhm c nc ngt in hnh hin nay tuy bao gm rt nhiu loi nhng ch thuc vo mt s nhm phn loi nht nh, c th k: c Nhiu vy (Polipteriformes), c Lng sn (Chondrostei), c Lng xng (Holostei), c Phi (Dipnoi), mt vi loi thuc b v h c trch (Clupeiformes, Notopteroidei, Osteglossoidei, Salmononoidei, Esocoidei, Mormyroidei), hu ht cc h thuc b c chp (Cypriniformes) v mt s h thuc vi b khc. Nhm c chu c nng mui cao hn phn b cc thy vc ven lc a, tip gip vi nc bin nn cn gi l c nc l. Trong nhm ny gm nhng loi thuc nhiu nhm phn loi khc nhau t lp c Sn n lp c Xng. S phn b ca cc loi c thuc nhm ny c lin quan nhiu n c im phn b ca cc loi c bin sng ven b vng thm lc a. Mi trng sng nc ngt c nhng im khc vi mi trng sng bin do c nhng c im v sinh thi, v a l, v lch s hnh thnh ring bit nn dn n mt s nt c trng v phn b nh sau: - Phn b theo i, nguyn nhn ch yu l do s phn b ca cc iu kin kh hu. - Phn b phng x, nguyn nhn do qu trnh pht tn ca nhng nhm c u th ch yu i t trung tm pht sinh l vng ng Nam chu .

24 - Phn ha cao cc lc a m nguyn nhn lin quan n cc iu kin sng cc lc a, s pht tn, cnh tranh v tin ha ca cc loi c. c trng phn ha cc lc a th hin r nh vng n - M Lai - u th ca h c Chp (Cyprinidae) v cc lc a chu u - , chu Phi, Bc chu M - s hn hp ca h chp (Cyprinidae) v cc h khc, Nam M v chu c khng c h Chp (Cyprinidae). - Cc khu h c nc ngt c trng tp trung phn b cc vng rng ln c h thng sng quan trng. Nguyn nhn l nhng ni ny mi c nhng iu kin sng thun li cho cc khu h c tn ti v pht trin. V d nh Nam M - l vng lu vc sng Amazn, Bc M l lu vc sng Mississipi, chu Phi l lu vc sng Congo, ng Nam chu l lu vc cc sng Trng Giang, sng Cu Long. Trc khi i su nghin cu c trng ca khu h c nc ngt thuc cc vng a l ng vt khc nhau cn nhc qua lch s pht tn ca cc nhm c nc ngt in hnh. n k Phn trng mi gp mt s c thuc non - Ostariophysi. Chng phn b theo hai vng n i ca tt c nm chu. Trong k ny nhng Ostariophysi nguyn thy (Characinoidei, Siluroidei) pht sinh vng nhit i Cu lc a c th l vng Tethys, ri t pht tn sang Nam M hoc theo cu lc a gia chu Phi v nam M qua ng Bc M. Tip theo sau, bt u t k Tam, pht sinh h Catostomidae m t tin c th l bn Characinoidei v t tin Ameuridae vng ng Nam chu , sau hai nhm ny pht tn ln pha Bc v sang Bc M. Tip theo, h c Chp Cyprinidae (t tin l Catostomidae) nguyn thy pht sinh vng nhit i ng Nam chu , nhm ny vi sc sng v thch nghi cao nhanh chng pht trin v phn ha thnh nhiu dng khc nhau, mt mt lm tiu dit cc loi c c c vng ny, mt khc theo cc ng pht tn ca cc nhm c trc pht tn sang chu Phi, pht tn ln vng n i chu u - , sang tip Bc M v lm tiu dit cc loi c c vn c cc ni ny. Cng thi gian ny cc nhm c Tia vy cao (Labrinthiformes, Matstacembeliformes, Ophiocephaliformes) cng pht sinhh vng nhit i ng Nam chu v bt u pht tn sang chu Phi, ln n i chu . 2.3.2. Phn vng a l phn b c nc ngt V phn chia vng a l phn b c nc ngt n nay c nhiu nh ng loi hc tin hnh. Do nhng dn liu v s phn b ca cc loi c nc ngt v cc khu

25 h c nc ngt a phng ngy cng nhiu v cng m bo nn s phn chia vng v nht l gii hn gia cc vng c chnh xc hn [8], [19]. P. Banarescu (1960) phn chia vng a l phn b c nc ngt nh sau (xem bng 1) (hnh 2.4, hnh 2.5):

Hnh 2.4. S a l phn b c nc ngt trn th gii (theo P. Banarescu)

26 Hnh 2.5. S cc vng a l phn b c nc ngt trn th gii (theo P. Banarescu)I. Ton Bc; II. n - Trung Hoa (ng Phng) (II1 l phn vng Trung Hoa; II2 l phn vng n - M Lai; II3 l phn vng Ty v II4 l phn vng min ni Chu ); III. Vng chu Phi (Ethiopian); IV. Nam M (Tn nhit i); V. Madagasca; VI. Chu c; VII. Tn Ty Lan (New Zealand); VIII. Cc o Thi Bnh Dng.

- Bc a: c vng Ton Bc (Holartic): gm vng C Bc (Palearctic) (u-Bc Phi) v vng Tn Bc (Neoarctic) (Bc M); - C a: gm vng n - Trung hoa hay cn gi l vng ng Phng (Oriental) v vng chu Phi (Ethiopian); Vng n - Trung hoa (hay cn gi Trung - n) c 4 phn vng l: Trung Hoa, n - M Lai, Ty v min ni Chu . - Tn a: vng Tn nhit i - Nam M (Neotropical); - Nam a: vng chu c (Australian). 2.3.2.1. Khu h c vng Ton Bc (Holartic) c trng: vng Ton Bc (Holartic) gm vng C Bc (Palearctic) (u--Bc Phi) v vng Tn Bc (Neoarctic) (Bc M). Khu h c c phong ph khng cao. C th: - n i , u h c Chp (Cyprinidae) chim u th. Ngoi ra, c mt s loi thuc cc h Catoslomidae, Esocidae, Ameiuridae. - Bc M, c s lng loi kh ng l hai h c Vy tia cao Centrarchidae v Percidae. Ngoi ra, c mt s loi c nguyn thy Poliodontidae, Amiidae, Hiodontidae. Ngun gc ca cc h Cyprinidae, Catostomidae, Siluroidei c pht tn t vng n - Trung Hoa. Phn b kh u t ng sang Ty n i , u, gia cao nguyn Trung th ngho. H Baican c hai h c c hu Comephoridae v Cottocomephoridae do h b cch li t rt lu i. Gn v pha Bc cc, xung quanh vng a trung hi, vng Tiu khu h c rt ngho. Min Bc cc ngho c nc ngt. Bc M khu h c nc ngt in hnh tp trung phn Trung v ng Bc M, ch yu thuc lu vc hai con sng Missouri v Mississipi. Ln pha Bc v xa v pha Ty Bc M th khu h c rt ngho. Bc M c mt s loi c min n i , u. iu chng t hai khu h c nc ngt ca Bc M v ca u, xa kia c mi quan h vi nhau v cng c ngun gc t min u, v c pht tn i sang vng Bc M. 2.3.2.2. Khu h c vng n - Trung Hoa hay ng Phng (Oriental)

27 c trng: phong ph nht trong cc khu h c, in hnh nht ca nhit i. Trong thnh phn c hin nay khng c dng c c, nguyn thy, ngoi mt s thuc Cyprinoidei v Siluroidei. Tnh cht phn b kh ng u k c vng qun o Indonesia (do qun o ny trc y c lin h vi qun o M Lai (Malayxia) v tch khi bn o M Lai (Malayxia) cha lu lm). Trong vng ny c cc thy vc trn cao nguyn ni cao c rt nhiu loi thuc cc h Homalopteridae, Gastromyzonidae, Sisoridae rt chuyn ha v hnh thi v c im sinh hc. Trong vng c mt s khu h c in hnh: ng bng Trung Quc, n , Malayxia.Vng ny c coi l trung tm pht sinh ca hu ht cc nhm c nc ngt hin nay trn th gii. 2.3.2.3. Khu h c nc ngt vng chu Phi (Ethiopian) c trng: thnh phn loi rt phong ph, in hnh ca vng nhit i. Gm nhiu h khc nhau t cc h nguyn thy nh: c Phi (Lepidosirenidae), c Nhiu vy (Polipteridae), Notopteridae, Osteoglossidae, Mormyridae, h c Chp (Cyprinidae), h c Chch (Cobitidae), Characinoidei, Siluroidei v cc h c Vy tia cao nh Nanidae, Anabantidae, Channidae, Mastacembelidae. Ni phong ph nht l khu vc Ty chu Phi t sng Snral n sng Cngo, c bit l sng Cngo. Khu h c cc sng Niger, sng Nil, h Tchad ging nhau cho php ta ngh trc y gia cc thy vc ny c mi lin h vi nhau. Vng ng Phi ngho c hn, khng c c Polipteridae, nhng li c thm mt s ging thuc h c Chp (Cyprinidae) do c pht tn t chu theo ng pha Bc. Nhng h ln ca vng ny c rt nhiu loi c hu, c bit thuc h c R phi (Cichlidae). H Nyasa c ti 174 loi c hu trong s 178 loi c y. Cc khu ngho c l: khu vc pha Nam thuc Zambia, khu vc pha Bc thuc sa mc Sahara. o Madagascar khng c c nc ngt in hnh. Chc chn o ny c tch khi lc a chu Phi t rt sm, sm hn thi gian hnh thnh cc nhm c nc ngt hin nay. 2.3.2.4. Khu h c nc ngt vng Tn nhit i - Nam M (Neotropical) c trng: khu h c vng ny rt phong ph v thnh phn loi, ngoi cc h c Phi (Lepidosirenidae), h c Sc vn (Nandidae), h c Tht lt (Osteoglossidae) c rt nhiu h thuc c Nheo Siluroidei (9 h) v Chanracinoidei (9 h). i b phn khu h c nc ngt ny tp trung lu vc sng Amazon, c th coi y l khu h c phong ph nht trn th gii vi khong 2000 loi, ch thua km

28 mt t so vi khu h c lu vc cc sng ln cn thuc pha Bc v pha Nam Colombia v Ecoador, Brazin. cc sng sui thuc dy ni Andes th ngho, nhng li giu mt s loi chuyn ha v a phng. Pha cc Nam ca Nam M khng c c nc ngt in hnh. Ngun gc c Nam M l t chu Phi hoc t ng Nam , Bc , Bc M pht tn ti nn khu h c ny c coi l cha cn bng, ang c nhiu bin i. 2.3.2.5. Khu h c nc ngt vng chu c (Australian) Khu h c nc ngt vng ny rt ngho. Ngoi c Phi chu c (Neoceratodus) v mt loi thuc Osteoglossidae l c nc ngt in hnh cn li u l c nc l. 2.4. Lch s t nhin, a l phn b c bin v c nc ngt Vit Nam 2.4.1. Lch s t nhin ca Vit Nam (theo Wikipedia) 2.4.1.1. Giai on tin k Cambri Giai on ny ko di khong 3 t nm t i Thi c (3,5 - 2,5 t nm) qua i Nguyn sinh (2.500 - 570 triu nm). i Thi c l ra thng ngun sng Chy v thng ngun sng Ba c xem nh l khin Thi c, di tch ca thi k to ni Kareli (cch y 2.500 triu nm). u i Nguyn sinh c hin tng tch dn y i dng vi s nng dn ca bin bo hiu s kt thc giai on v i dng, bt u giai on v lc a vo nguyn sinh gia mun. Cnh quan tin k Cambri l cnh quan hoang mc s khai v vo i Thi c, kh quyn v thy quyn cn rt mng, c to thnh t cc cht d bay hi trong qu trnh phun tro ca ni la, khng kh giu CO2, CH4, NH3, H2O v hu nh cha c O2. n i Nguyn sinh bt u c mt t thc vt sng di nc dn ci to thnh phn kh quyn, lng CO2 gim dn, tng dn O2. Cui i Nguyn sinh hnh thnh mi trng oxy ho r rt, hnh thnh cc loi to tch ly CaCO3, dn n vic hnh thnh cc tng vi, tin ti pht trin mt s loi dng x, vi khun, ng vt khng xng sng. S sng si ng trn lnh th nc ta. 2.4.1.2. Giai on c kin to Giai on ny din ra trong i C sinh v i Trung sinh i (570 - 65 triu nm). Vn ng to ni Caleoni t k Cambri sm n k Devon sm m rng khi vm sng Chy n ng Vn (H Giang) v Trng Khnh (Cao Bng) v pha Bc; pha ng n Qung Ninh; pha Nam n ng bng sng Hng ni Bc ca

29 Vit Nam vi Nam ca Trung Quc thnh nn mng Vit - Trung. Ra pha Nam nn Kon Tum thuc Nam Trung B v Nam B tn ti ch thm lc a. Vn ng Hecxini ko di t k Cambri sm n k Permi tc ng mnh vng Ty Bc m rng di st tch sng . Ti a khi Kon Tum vn ng Hecxini biu hin qua xm nhp granitoit, vng cc Nam Trung B hnh thnh vng cung ni la Carbon thng: Permi (C3-P) gm bazan v andezit. Cc qun o Hong Sa v Trng Sa l tn d ca v lc a Hecxini sau b tch dn, ln chm san h pht trin bn trn. Vn ng to ni Indoxini xy ra vo k Trias (t 225 n 180 triu nm) din ra mnh nht vng sng . Ti cc khu vc nn mng Caledoni ng Bc ch c kin trc vng chng ni lc ph trm tch lc a cha than vng sng Hin, An Chu, Hn Gai. Ti khu vc nn mng Indoxini cc trng nh Hong Sn c lp y trm tch lc nguyn xen phun tro riolit v xm nhp granit. Vn ng Indoxini hon ton hnh thnh ch v lc a trn ton lnh th ca Vit Nam. Vn ng Kimeri vo cc k Jura v Kreta cui trung sinh i tip tc lp y cc bn trung ni lc bng cc trm tch lc a mu v hot ng macma (ch yu l riolit) c kt v lc a trn lnh th ca Vit Nam. T cnh quan s khai tin k Cambri n i C sinh pht trin cnh quan hin sinh (Paleozoi) vi s pht trin ca gii thc vt v ng vt. n k Silua xut hin cc loi cy bi nh thch tng, dng x pht trin trn cc vng t m. C v cc loi chn t bt u xut hin. Vit Nam lc ny cn ch yu nm trong ch bin nn ch yu l cc ng vt bin nh san h v cc loi khc. Vn ng to ni Caledoni phn ho kh hu theo chiu cao v chiu ngang, hnh thnh nhng min t m v kh nn vo k Devon hnh thnh nhng cnh rng thc s, ng vt lng c v c pht trin. n k Carbon cnh quan rng pht trin rng ri, ch yu l thch tng, dng x, mc tc cao hng chc mt, ngoi ng vt lng c xut hin cc loi b st v su b. Cc cnh rng ny cht i hnh thnh nhng b than ln trn th gii, song khng thy Vit Nam. Sang k Permi sau vn ng to sn hecxini, cnh quan kh hn pht trin rng ri nn nhiu dng dng x cht i, xut hin cc thc vt ht trn. T cui k Trias, u k Jura, kh hu nhit i m pht trin cc cnh quan rng, to iu kin cho tch ly than, cc m than ln ca nc ta hnh thnh trong thi gian cui k Trias, cc ho thch cho thy c nhng cy c bch tn ng knh

30 t n 40 - 50 cm, kh hu lc ny nng m vi ma kh ngn biu hin trn cc vng ng tm ca ho thch cy. Ngoi c bch tn cn thy dng x ln thc vt ho than Hn Gai v di tch mc tc trong ip sng Hin. Rng, m ly nng m to iu kin cho khng long khng l pht trin m ho thch ca chng thy trm tch k Jura v v k Creta vng Lao Bo. T k Jura xut hin chim v mt s ng vt c v, tao tin cho sinh vt pht trin vo i Tn sinh. 2.4.1.3. Giai on tn kin to Giai on ny din ra trong i Tn sinh cch y khong 65 triu nm. Din ra mnh trn lnh th Vit Nam do v tr trn bnh kin to khu vc. Mang tnh k tha cc kin trc c. Hot ng nng v st din ra theo tng t, lm thnh cc bc a hnh trn lnh th Vit Nam vi 6 chu k. B mt bn bnh nguyn c Paleogen hnh thnh cch y 65 n 38 triu nm trong iu kin kh hu nng m, cc hot ng ngoi sinh san bng cc khi ni, lp y cc vng trng bng cc trm tch h v cc b than, du kh. B mt ny sau c nng ln v thy cao 2.100 2.200 m trn dy Fanxipan. B mt bn bnh nguyn c Paleogen b ph v vo Miocen sm (N11) khi vn ng to ni Hymalaya tc ng nng cao lnh th nc ta, to nn chu k 1. Cui chu k 1 hnh thnh bn bnh nguyn cao 1.500 - 1.800 m Sapa. Chu k 2 din ra vo Mioxen mun (N12) lm a hnh nng cao hn, ct x b mt bn bnh nguyn ca chu k 1. Cui chu k 2 li hnh thnh bn bnh nguyn m di tch cn thy trn cao 1.000 - 1.400 m ( lt nm trn cao 1.500 - 1.600 m). Chu k 3 din ra vo Pleistocen sm (N21) cch y khong 5 triu nm vi cng nng mnh, trung bnh 500 m, cc i n 1.200 - 1.500 m nh cc dy ni Fan xi pan, Pu si lung. B mt bn bnh nguyn ca chu k 3 hin nm trn cao 600 - 900 m, kh hu nng m. Chu k 4 din ra vo Pleistocen mun (N22), nng mnh Nam Trung B, cn min Bc nng mc trung bnh, i theo l hot ng phun tro bazan mnh Ty Nguyn v Nam Trung B. Trong trm tch ca chu k 4 tm thy ho thch v di ch ca ngi vn. Chu k 4 li di tch trn cao 200 - 600 m. Kh hu bt u lnh dn do s xm nhp ca khng kh lnh t phng Bc xung. Chu k 5 din ra vo Pleistocen sm - gia (QI-II) trong t cch y 2 triu nm nng cao v ct x b mt bn bnh nguyn ca chu k 4 v lm st vng chu th sng Cu Long. Hot ng nng st km phun tro bazan c Lc v ng Nam B. Hnh thnh cc o ni la ngoi bin nh Cn C, L Sn, Ph Qu. Di

31 tch ca a hnh chu k 5 l cc trm tch ph sa c ng Nam B, cc n ct Bnh Thun, cc thm bin trn 20 m; cc thm sng 25 - 45 m v b mt bn bnh nguyn l cc bc thm xm thc v xm thc - tch t vng ni trn cao 25 - 200 m. Chu k 6 bt u vo Pleistocen mun (QIII) ko di n tn ngy nay vi cng yu. Cc trm tch ca chu k ny l cc nham tng vng vnh ven bin, cc trm tch sng, h. Chu k ny gn vi t bng h Wurm v bin tin Flandrian cch y khong 17 n 10 nghn nm, cc t ngng ngh ca bin tin hnh thnh cc thm ct trng cao 4 - 5 m, cc thm bin cao 2 m. o hn Tro pha nam o Ph Qu hnh thnh nm 1923 l sn phm ca chu k 6; hng lot cc sui nc nng l kt qu ca chu k hot ng ny. Hin nay vn cn cc hot ng ca ng t in bin v trn di t t Ty Bc xung Bc Trung B. Vo Pleistocen kh hu lnh dn (sau vn ng to ni Hymalaya) lm thay i cnh quan, lm a dng cc ging loi sinh vt Vit Nam, kh hu nng tr li vo Holocen. 2.4.2. Lin h gia cc con sng c Vit Nam vi cc con sng c ng Nam Ti cc khu vc c nhiu bin ng a cht kh hu, s hnh thnh v pht trin ca cc lu vc sng lun dn ti s thay i dng ca cc con sng. Tm hiu cc dng sng c cho chng ta gii thch mt cch ng n v quan h gia cc khu h. S nng ln dy ni Himalaya l tc nhn dn ti s hnh thnh nhiu dy ni ln thuc bin gii Vit - Trung, s nng ln ca vng cung Min in - Malayxia, s nng ln ca cao nguyn Ty Tng v cao nguyn Vn Nam. iu ny dn n s thay i ca nhiu lu vc sng. Hnh 2.6 cho thy sng Hng trc vn ng to ni Himalaya (a) ni vi sng Dng T, sau vn ng to ni Himalaya mt phn sng Hng c c nhp vo sng Dng T hin nay, sng Hng Hin ti ngn hn sng Hng c rt nhiu. S lin h gia sng Hng c v sng Dng T l mt c s quan trng gii thch t l cao cc loi c c ngun gc Trung Hoa ca khu h c sng Hng. Sng M Ping c v sng Mekong c u vo vng bin Nam B gn ca sng Cu Long hin nay. Sng Salween c di hn sng Salween hin ti, thng ngun sng ny trc y rt gn vi sng Mekong. Hin tng bng h vo thi k Pleistocene, bin thoi, mc nc bin thp dn n s hnh thnh lc a Sundaland vi h thng sng Great Sunda, h thng sng ny c s lin h cht ch vi sng Mekong (hnh 2.6), phn ra ngoi ca lc a

32 ny bao gm c o Hi Nam v vy, cc dng sng trn o Hi Nam c th c s lin h vi cc con sng vng Bc B v Bc Trung B.

Hnh 2.6. Cc dng sng trc v sau vn ng to ni Himalaya 2.4.3. Mt s nt chnh v iu kin t nhin ca Vit Nam [2, 3, 4, 5, 6, 7, 8] 2.4.3.1. V tr a l Vit Nam l mt nc nm v tr tn cng ng Nam ca lc a chu , gn trong vng ni ch tuyn, tc l vng nhit i ca bn cu Bc. Din, tch lnh th 332.000 km2, tri di theo v 23022N - 8030N v kinh 102010E - 109021E. i b phn lnh th c bao ph bi i ni (chim 3/4), c ni ko di ra st bin, thm ch cn lan ra bin cc qun o. Hng ni ch yu l Ty Bc - ng Nam, cc hng bao gm kinh tuyn v v tuyn, gn nh thng gc vi hng gi ma Ty Nam, thi t thng 4 n thng 10 tc ng trc tip ti ton b Nam B, vng Ty Trng Sn v Ty Bc B; gi ma ng Bc thi vo Vit Nam t thng 9 n thng 1 nm sau, bao gm gi kh lnh b vo Bc B v Bc Ngh An mang li ma ng kh rt v gi ma m lnh b vo Vit Nam t Nam Ngh An n Trung Trung B t thng 9 n thng 12, lm cho ma ng lnh v m. Cu trc sn vn v a hnh to ra s phn ha kh hu thy vn t Bc xung Nam, t ng sang Ty. i ni khng cao nhng him tr, a hnh chia ct mnh, va dy li va su

33 vi nhng sn dc to ra mng li kh dy. Kh hu nng lm, ma nhiu nn c nhiu dng hnh mt nc. Dy Hong Lin Sn v Trng Sn to nn hai ch nhit kh hu khc nhau bao trm trn ton b lnh th Vit Nam. pha Ty, c hai ma kh nng v ma nng r rt. iu to nn nhng iu kin thun li, thch hp vi nhng cy rng l vo ma kh. pha ng, s phn bit hai ma ma nng v ma kh lnh hay hi kh lnh khng r lm. V vy, nhng cy chu lnh, c chi bp, l cng hay rng l trong ma ng chim u th. T Bc vo Nam, ngoi nhng nt chung nh trn, mt s dy ni chy ra st bin ngn chn cc hng gi lm cho kh hu trong vng c s phn ha khc nhau. cng l mt trong nhng nguyn nhn lm cho thnh phn thc vt v chng mc nht nh c thnh phn ng vt khc nhau. V d: t Ngh An n o Ngang, t o Ngang n o Hi Vn, t o Hi Vn n o C v Nam o C. V ai cao, c th tng qut ha mt cch n gin ly cao 700 m min Bc, 900 m min Trung v 1000 m min Nam tr ln c coi l ai c kh hu m, mt hoc lnh trong ma ng. C th chia gii hn ny thnh mt h trng chuyn tip gm 8 kiu khc nhau (theo Phm Quang Anh, 1996), nhng thc t y ch l nhng phn kiu trong tng vng mt. ng bng chu th min Bc (sng Hng) v min Nam (sng Mekong) ni vi nhau bi min Trung ven bin, nhiu ni v hp. Chiu ngang rng nht min Bc khong 600 km, ni hp nht min Trung cha c 50 km. Nn tng cu thnh lnh th Vit Nam l khi kin to Hoa Nam, h un np Lo - Vit, khi nh Kon Tum, khi Lm ng - Si Gn, khi kin to chu th Nam B. Lnh th Vit Nam cng chu nh hng ca qu trnh tc ng ca nhng bin i mc nc bin ng Nam chu ca Thi bnh dng. Thm vo , Vit Nam l ni giao lu ca cc yu t dy ni Hymalaya chy theo hng Ty Bc - ng Nam v cc dy ni t Nam Trung Quc chy theo hng Bc Nam. Nhng c im trn y c nh hng n khu h ng vt, thc vt. 2.4.3.2. Sng ngi Cc sng ln ca h thng sng Hng v sng Mekong u bt ngun t Trung Quc chy qua Vit Nam ra bin. Bin ng l lu vc tp trung nc ca sng ngi Vit Nam. Mt s sng nh Bng Giang - K Cng, Nm Rm, Sesan - Srepok vi

34 din tch lu vc khong 13% din tch v khong 12% dng chy ca ton lnh th. Tuy chy vo cc sng Ty Giang v Mekong nhng cui cng cng vo bin ng [4]. Vi iu kin nhit i lng ma phong ph trn lnh th nc ta m 3/4 l i ni, to iu kin thun li cho s hnh thnh dng chy vi li tiu nc ra bin kh dy. Mt sng, sui c dng chy thng xuyn trung bnh t 0,6 km/km2. Dc b bin trung bnh 20 km c mt ca sng. Ton quc c ti 2.360 con sng ln, nh (t ph lu cp 1 -6) vi mt gia cc vng t 0,3 km/km 2 n 4 km/km2. Trong c 106 con sng chnh cn li l cc sng ph theo cc cp khc nhau, ch yu l cp II, cp I, cp III, cp IV. Nhn chung, vng c mt sng rt dy t 1,5 - 2 km/km2 nh vng ni cao Hong Lin Sn, Ty Cn Lnh, Mng Ci, o Ngang, o Hi Vn, thng ngun sng ng Nai c bit ng bng sng Cu Long, ng Nam chu th sng Hng c mt 2 - 4 km/km2. Nhng vng ni trung bnh, ni thp, lng ma tng i ln t 1.800 - 2.000 mm nh vng cnh cung Ngn Sn, vng ni Qung Ninh, trung lu sng ng Nai, sng Thu Bn, mt s sng thuc ng Trng Sn, thng ngun cc sng Ty Nguyn c mt t 1,0 - 1,5 km/km2. Cn li i b phn cc sng c mt trung bnh t 0,5 - 1 km/km2. c bit mt s vng vi nh Tr Lnh, Trng Khnh, Qung B, Bc Sn, Mc Chu, K Bng, Bc v Trung Ty Nguyn, Thun Hi c mt t di 0,3 - di 0,5 km/km2. Mt sng vng ng bng tuy dy nhng vn khng m bo tiu nc l v nc ma ti ch nn ngp lt vng ng bng thng xy ra. Hng nm, yu cu tiu nc ca ng bng sng Hng t thng ngun v v ma ti ch xp x 150 t m3 nc, ng bng sng Cu Long khong 520 t m3 nc, c tnh mt sng, knh rch phi t 10 - 12 km/km2 nhng mt sng hin nay mi ch l 3 - 4 km/km2. V vy, c nhiu vng ngp nc. Cc con sng nc ta c nhiu dng: - Cc sng ln (106 con sng), di, rng v c ngun li c phong ph nh sng Tin, sng Hu, sng ng Nai, sng Hng, sng Thi Bnh.

35 - Cc sng nhnh, sng con c ngun li c km phong ph hn nh sng L, sng , sng Cu, sng Thng, sng Lam, sng M, sng Thu Bn, sng Ba, sng Si Gn - Cc sng t nhin c kh nng nui c nh cc sng ct, sng thin nhin nh vng ng bng: sng C L, sng Ng, sng Chu Giang. - Cc sng o, trung i thy nng nh sng ung, sng Bc Hng Hi v hng lot cc knh mng thy li. Ngoi ra cn c h thng cc sui, ngi phn b khp vng ni v trung du. Tuy nhin, c nc c 9 h thng sng ln c din tch lu vc t 1.000 km2 tr ln.Bng 2.1. Cc h thng sng Vit Nam c din tch lu vc trn 10.000 km2

TT

H thng sng

Chiu di sng (km) Ton Trong b nc 243 556 288 512 530 205 388 410 361 205 388 635 230

Din tch lu vc Ton b Trong nc 10.902 61.300 12.680 17.600 17.730 10.496 13.800 37.394 71.000 5.272 721.000 10.800 9.470 Ngoi nc 1.478 82.300

I 1 2 3 II 4 5 6 7 III 8 9

Bc B K Cng-Bng Giang Hng Thi Bnh Trung B M C Thu Bn Ba Nam B ng Nai Cu Long 249 1161 12.380 143.000 12.680 28.400 27.200 10.496 13.800 42.666 795.000

635

Ngun: Nguyn Vn Ho, 2001 [4] Cc sng ny khng nhng cung cp ngun nc, ngun c cho cc loi hnh thy vc nc khc nh ao, h, h cha v rung m cn to ra nng sut v sn lng c t nhin rt ln nhiu vng trong c nc; nht l vng ng bng sng Cu Long v ng bng sng Hng. 2.4.3.3. Cc m h t nhin v h cha m h nc ta c hai dng: h t nhin v h cha (h nhn to).

36 - H t nhin: l h do thin nhin to ra, l nhng vng trng cha nc, to thnh mt nc rng, mt th nc lu thng chm v khng th trc tip thng ra bin. Cc h t nhin phn b ch yu ng bng Bc B n vng ni, trung du bc B v vng khu V; cn cc vng khc th rt t. Mt s h t nhin ng quan tm l h Ba B, h Ty, m Chnh Cng, m Vc, m Dng (min Bc), m Chu Trc, m An Kh, m Loan (min Trung), h Lc, bin H (vng Ty Nguyn) Theo thng k s b ca Nguyn Vn Ho (1993, 1997), nc ta c c 231 m, h t nhin, phn b 38 tnh, vi tng din tch 34.600 ha. - H cha (h nhn to): do chn cc sng gi nc phc v cho vic chng lt, thy li, thy in v ti tiu cho nng nghip m hnh thnh. Trong khong 30 40 nm gn y h cha nc ta pht trin kh nhiu. Theo s liu iu tra ca Vin Kinh t v Quy hoch Thy sn (1995), cc h cha nc ta gm 2.470 h, vi din tch 183.580 ha theo cc quy c khc nhau, phn b 35 tnh, thnh ph. Cc h c nh di 100 ha chim 96,1% v s lng, din tch chim 11,9%. Ngc li, h t 100 ha tr ln v s lng ch chim 3,9% nhng din tch li chim ti 88,1%. Cc h cha tiu biu min Bc l h Ha Bnh, h Thc B, h Ni Cc, Cm Sn, ng M - Ngi Sn, Sui Hai, Quan Sn Cc h cha tiu biu Bc Trung B l h Sng Mc, h K G, h Cm Ly. Cc h cha tiu biu Nam Trung B l h Ph Ninh, h Ni I. Cc h cha tiu biu Ty Nguyn l h Ea Kao, Yaly, h c Uy. Cc h cha tiu biu ng Nam B l h Tr An, h Du Ting 2.4.3.4. Cc ao rung C 58.088 ha ao v 548.000 ha rung c kh nng pht trin ngun li c. Ao tp trung vng Bc B c 44.588 ha, chim 76,76%. Trong , vng ng bng sng Hng c 29.600 ha, chim 50,96%, cn trung du v min ni 14.988 ha, chim 25,8%, tip n l vng Nam B c 8.500 ha, chim 14,63%, trong ng bng sng Cu Long 7.500 ha, chim 12,91%, cn ng Nam B 1.000 ha, chim 1,72%. Cc tnh min Trung v Ty Nguyn ao rt t. Rung c kh nng pht trin thy sn tp trung ln nht l vng Nam B vi 496.500 ha, chim 90,59%. Trong , ng bng sng Cu Long vi 484.500 ha, chim 88,4%; cn ng Nam B vi 12.000 ha, chim 2,19%; tip n l vng Bc B vi 45.550 ha, chim 8,31%, trong ng bng sng Hng vi 31.000 ha, chim

37 5,66%; cn trung du v min ni vi 14.550 ha, chim 2,65%; cc vng khc c rt t hoc khng c. Tm li, h thng cc vc nc nc ta rt nhiu, to nn mng li dy c vi cc a hnh kh phc tp: vng trung du, vng ng bng v ca sng ven bin vi cao v vng sinh thi khc nhau, lm cho khu h c nc ngt nc ta rt phong ph, a dng v c o. Vng ng bng sng Cu Long v ng bng sng Hng c ngun li thy sn phong ph, to thnh hai va c ln ca c nc. 2.4.4. V tr a l ng vt hc ca Vit Nam Vic xc nh c tnh a l ng vt ca mt khu h ng vt ca mt vng lnh th v v tr ca vng trong h thng phn min a l ng vt th gii c th c gii quyt theo nhiu cch, bng nhiu phng php khc nhau ty i tng v ty quan im ca mi tc gi. Mt trong nhng phng php c nhiu c s hn c l da vo s phn tch ng n v su sc cu trc a l ng vt ca thnh phn loi; tm hiu v xc nh c cc nhm ng vt trong thnh phn ca khu h ng vt nghin cu, ch bit quan trng l xc nh c cc nhm ng vt c c tnh phn b hp mang nhiu tnh cht c trng ca khu vc. Tnh cht c trng ca mt khu h ng vt ca mt vng lnh th c th hin v bc c hu ca khu h l t l s loi c hu v bc phn loi ca cc yu t c hu [8]. Vn v tr a l ng vt hc Vit Nam c lin quan ti vn phn vng a l ng vt vng n - Trung Hoa ni chung, cng nh phn vng ng Dng. Vic gii quyt cc vn ny i hi phi c nhng dn liu y v chnh xc v thnh phn loi v phn b ca nhm ng vt cc khu vc trong phn vng a l ng vt ng Dng, cc phn vng ln cn v c vng a l ng vt vng n Trung Hoa ni chung. V c tnh v v tr a l ng vt hc Vit Nam c mt s tc gi bn lun trn nhng nhm ng vt khc nhau. Di y, chng ti gii thiu mt s quan im ch yu ca cc tc gi khi nghin cu v c. 2.4.5. a l phn b c bin Vit Nam [19,21] Theo P. Chabanaud (1926) phn bit c bin Vit Nam thnh bn nhm: - Nhm c ph bin; - Nhm c sng n dng m Vit Nam l gii hn cao nht;

38 - Nhm c sng bin Nht Bn m y l gii hn thp nht; - Nhm c sng c trng ring ca vng n - M lai (Malayxia). Besednov L.N. (1967, 1970) nghin cu c trng phn b cc loi c bin vnh Bc B v phn Ty Bc ca bin ng kt lun: Khu h c vnh Bc B kh sai khc vi khu h c bin Nam Dng, nht l vi vnh Thi Lan trong khi rt gn vi khu h c bin Nam Nht Bn, ng Hi v o Hi Nam. Blanc - Fourmanoir (1964) nghin cu c bin dc b bin Campuchia chng minh khu h c y (vnh Thi Lan) rt ging vi khu h c bin Ceylon (83,8%) v ging rt t vi khu h c bin b pha ng bn o ng Dng. Nh vy cho php kt lun khu h c bin vnh Bc B v b bin pha ng Trung B (c th c Nam B) khc vi khu h c bin vnh Thi Lan. Tng s loi c bin thng k c l 2.475 loi. Khu h c bin c c trng l s h nhiu nhng s ging khng nhiu, c bit s loi trong mt ging rt t, rt nhiu h ch c 1 ging, 1 loi nh: Chimeridae, Ophidiidae, Batrachidae. a s cc loi c bin Vit Nam phn b rng trong vng bin thuc khu vc nhit i v cn nhit i. Tuy vy, thnh phn loi c trong tng vng bin c bit l vng bin min Trung c nhng im khc bit r rt vi cc vng bin Bc B, ng Nam B v Vnh Thi Lan [2]. Mt s loi mi ch gp bin min Trung nh c Trp vng (Tais tumifrons), c Khime (Chimaera fantasma). * Khu h c vnh Bc b c mt s c im sau: - Trong s 748 loi c thng k c vnh Bc B c 191 loi c trng ca nhit i pha Nam m gii hn cao nht y, 81 loi c trng ca n i m m y l gii hn thp nht, 476 loi phn b rng, s loi c hu rt thp. - Khu h c vnh Bc B l mt khu h c tng i tr (hnh thnh cch y 2 3 nghn nm). - Khu h c vnh Bc B c xp vo tnh a l ng vt bin Hi Nam, cng vi Nam Nht Bn, Hong Hi, ng Hi hp thnh phn vng a l ng vt bin n - Ty Thi bnh dng. - c trng ca khu h c vnh Bc B th hin r hai mt: nhit i v n i. c trng nhit i: nhiu loi, s lng loi sng tng mt v gn y cao hn chnh y, s lng loi n sinh vt ni nhiu hn s lng loi n y, nhiu loi n

39 tht, nhiu loi sng nh c, thiu nhng n c tp trung ln, trng tng t, chuyn ha su v thc n v v ch . c trng n i: ngho v thnh phn loi so vi cc vng nhit i khc, thnh phn loi c thay i theo ma do c mt s loi c ngoi khi di c vo vnh vo ma h v ri vnh vo ma thu. C tp trung mt tng i dy vo ma ng, c hin tng di c thng ng, vng nm trn vy xut hin kh r. C th chia khu h c vnh Bc B ra thnh 4 nhm sinh thi: tng mt, gn y, y v rn san h. - C n sinh vt ni tng mt: Dussumieria hasselti. Sardinella jussieu, S. aurita, Ilisha elongala (Clupeidae), Thrissa hamiltoni, T. setirostris (Engraulidae), Caranx chrysophrys, C. malabaricus, C. leptolepis, C. malam, Decaplerus maruadsi (Carangidae), Leiognathus equulus (Leiognathidae), Enthynnus affinis, Auxis thazard (Scombridae). - C n tht (d) tng mt: Carcarhinus menisorrah, C. sorrah (Carcarhinidae), Sphyrna lewini (Sphyrnidae) Chirocentrus dorab (Chirocentridae), Sphyraena jello (Sphyraenidae), Trichiurus S.commersoni (Scombridae). - C n gn y v y: Arius thalassinus (Ariidae), Himantura uasnak (Dasyatidae) Epinephelus (Serranidae), Therapon theraps (Theraponidae), Priacanthus tayenus, P. macracanthus (Priacanthidae), Nemipterus japonicus, N. virgalus (Nemipteridae), Pomadasys hasta (Pomadasyidae), Argyrops spinifer, Parargyrops edita (Sparidae), Upeneus moluccensis, U. sulphureus, U. bensasi (Mullidae), Psettodes erumei (Psettotidae). - C n tht (d) tng y v gn y: Saurida tumbil, S.undosquamis, Trachynocephlus myops (Synodidae), Muraenesox talabonoides (Muraenesocidae), Lutfanus erythropterus, L. scaber (Lutfanidae). * Khu h c bin vnh Thi Lan v dc b bin min Nam c mt s c im sau: - L mt khu h c mang nhng nt c trng ring, l khu h c ca mt vnh nng, rng, thuc vng bin nhit i ging vi cc vnh thuc n dng. Khu h ny kh sai khc vi khu h c dc b pha ng min Nam. haunela (Trichiuridae), Scomberomorus guttatus,

40 - Khu h c ny c tnh c n 1000 loi. Nu theo cch phn chia vng a l ng vt bin th khu h c ny thuc tnh M lai (Malayxia), phn vng n - M Lai, vng n - Ty Thi bnh dng. - S b nh gi c cc loi thuc cc h sau: - Chanidae (Chanos chanos); - Clupeidae (Dorosoma nagus, Dussumieria acula); - Engraulidae (Stolephorus commersi, Alosa kannagurla); - Muraenidae (Muraenesox cinereus, M. talabonoides); - Mugilidae (Mugil seheli, M. phaniceps); - Latidae (Latos calcarifos); - Serranidae (Epinephelus argus, E. latifasciatus, E. pachycentrus); - Carangidae (Decapterus maruadsi, Caranx malabaricus, C. hippos); - Thunnidae (Euthynnus gaito); - Scomberomoridae (S. commersoni, S. guttatus). Ngun li c y v gn y ca Vnh Thi Lan rt phong ph l cc ging: Nemipterus, Saurida, Upeneus, Lutjanus, Priacanthus. Ngun li c tng mt ca b bin pha ng Trung B li rt giu, l cc loi thuc cc ging: Sardinella, Clupanodon, Dorosoma, Thrissa, Anchoviella, Thynnus, Auxis, Scomberomorus Vng bin ca sng Cu Long (ng bng Nam B) li rt nhiu cc loi c nc l v cc loi c di c t bin vo sng. Khu h c ca sng ven bin Vit Nam: - Da vo c im a l t nhin, Mai nh Yn chia khu h c ven bin Vit Nam thnh 6 n v a l, cc tc gi xp cc loi theo tng vng nh sau: + Vng I: ven bin tnh Qung Ninh v Hi Phng c 105 loi. + Vng II: ven bin Thi Bnh v Nam nh c 53 loi. + Vng III: ven bin Thanh Ha, Ngh An v H Tnh c 105 loi. + Vng IV: ven bin min Trung n Thun Hi c 52 loi. + Vng V: ven bin ng Nai n Cu Long c 86 loi. + Vng VI: ven bin cc tnh C Mau v Kin Giang c 46 loi. - V Trung Tng (2009) thng k t cc ti liu c 615 loi trong 120 h thuc 29 b. B c Vc (Perciformes) ln nht c 339 loi (gn 55,12%) tng s loi

41 v 53 h (chim 44,17% tng s h). C 8 b c mi b ch xut hin mt vi loi trong vng ca sng. Nhng b xp theo th t sau: Perciformes, Clupeiformes, Pleuronectiformes, Mugiliformes, Tetraodontiformes, Anguilliformes, Beloniformes, Siluriformes l nhng b c nhiu ging loi. Nhng h a dng v s loi, t 47 loi n 19 loi theo th t: Gobiidae (47 loi), Carangidae, Sciaenidae, Serranidae, Clupeidae, Cynoglossidae, Tetraodontidae, Engraulidae (19). Nhng h t 10 loi tr ln ng gp 326 loi, chim gn 52% tng s. Trong thnh phn khu h c c khong 42 h ch c 1 loi, chim 35% s h v 6,8% s lng loi [13]. 2.4.6. a l phn b c nc ngt Vit Nam 2.4.6.1. Thnh phn loi c nc ngt Danh lc cc loi c nc ngt bit ca Mai nh Yn trong ng Ngc Thanh v cc cng s (2002). Tc gi da ch yu vo danh sch c nc ngt ca B Thy sn (1996) c chnh l v sa cha cht t. Khu h c nc ngt Vit Nam gm 546 loi thuc 226 ging, 57 h v 18 b. B Cypriniformes chim ln nht c 378 loi, b Siluriformes c 88 loi, b Perciformes c 70 loi [18,20]. Trong s cc loi c bit c ti 60 loi c hu, s ln l loi c hu cho Vit Nam, mt s h sng Mekong l c hu chung vi cc nc lng ging. Nhiu loi mi c m t gn y. So snh vi cc nc c din tch tng t nh Vit Nam, th Vit Nam c coi l t nc c a dng c nc ngt cao. Theo Nguyn Vn Ho (2005) thng k c t cc ngun ti liu khc nhau cho thy Vit Nam c 1.027 loi v phn loi c nc ngt, xp trong 427 ging, 98 h v 22 b [4,5,6]. 2.4.6.2. c tnh v quan h a l ng vt ca khu h c nc ngt Nhiu nh ng loi hc v a ng vt hng u th gii coi khu h c vng Trung - n hay ng Phng l phong ph nht v l trung tm pht sinh ca hu ht cc loi c nc ngt trn th gii [Darlington (1957), Briggs (1979) Banarescu, Nalbant (1982) v Kottelat (1989)]. ng Ngc Thanh (1980) da trn s tng kt c chn lc v ph phn quan im phn vng a ng vt nc ngt trc y, ng thi da trn kt qu iu tra khu h ng vt khng xng sng nc ngt Bc Vit Nam a ra mt h thng phn vng a ng vt nc ngt Bc Vit Nam nh sau: ng vn coi Vit Nam nm trong vng Trung - n (Indo-China theo Berg, 1933, 1948, 1949 v Starobogatov,

42 1970), nhng ng tch Bc Vit Nam - Hoa Nam thnh mt phn vng c tnh cht chuyn tip gia phn vng Trung Hoa v phn vng n - M Lai c gii hn t pha Nam ni Tn Lnh ti lu vc sng Hng, sng C. Thnh phn loi y mang tnh hn hp cc yu t Trung Hoa v n - M Lai. Phn vng ny c 2 tnh Bc Vit Nam v Hoa Nam. Tnh Bc Vit Nam gm trung v h lu sng Hng, sng M, sng C, cc sng ng Trng Sn cho ti o Hi Vn. ng coi y l gii hn phn b tuyt i thp v pha Nam ca cc loi n i v cn nhit i. Phn vng n - M Lai pha ng chu c gii hn t pha Nam bn o ng Dng (pha Ty Trng Sn, pha Nam o Hi Vn). Phn vng ny c tnh Mekong bao gm c Lo, ng Thi Lan, Campuchia v Nam Vit Nam. Tm li, theo ng Ngc Thanh (1980), ng vt nc ngt Vit Nam nm trong vng n - Trung Hoa, trong phn vng Bc Vit Nam - Hoa Nam v phn vng n - M Lai. Hai tnh a ng vt Bc Vit Nam v Mekong c ng ranh gii l ng phn thy Trng Sn ni vi Hi Vn. Phn chia a ng vt vng a ng vt ng Phng c Y. Taki tho lun, tc gi cho rng vng a ng vt ng Phng c 2 phn vng; phn vng Trung Hoa v phn vng n - M Lai. Phn chia ca Y. Taki da trn cc s liu v c nc ngt v vy y l s phn vng ng tin cy i vi nhm c. c tnh v quan h a l ng vt ca khu h c nc ngt khu vc ng Dng ni chung v Vit Nam ni ring c mt s tc gi nghin cu hoc cp ti (Sauvage, 1884; Chevey et Lemason, 1937; Mai nh Yn, 1963, 1973, 1988, 1991, 1995). Da trn nghin cu v thnh phn loi c nc ngt kh y t trc ti nay: Mai nh Yn (1973) [18], Nguyn Thi T (1983) [15], Mai nh Yn v Nguyn Hu Dc (1991, 1995) [3], Nguyn Vn Ho (1993, 1998) kt lun khu h c nc ngt min Bc Vit Nam rt gn vi khu h c nc ngt ca phn vng Nam Trung Hoa v rt xa vi khu h c nc ngt n - Malayxia, c th l cc khu h c ca Thi Lan, ca Malayxia v ca Campuchia. Trong khi A. Krempf v P. Chevey (1933) khi so snh thnh phn khu h c nc ngt ca Nam B v ca Campuchia ln lt vi khu h c nc ngt Indonexia, n , Min in li cho bit khu h c nc ngt min Nam Vit Nam v Campuchia rt ging vi Indonexia v rt khc vi n , Min in v kt lun: Hai khu h ny c cng chung ngun gc do mt h thng sng ln gm 2 sng: Grand Fleuve indochinois v North Sudan

43 river trc y cng chung ra bin ng, nay v bin ng lm chng cch li. H. M. Smith (1945) nghin cu khu h c Thi Lan cng kt lun tng t: Cc khu h c Nam Dng, ng Dng, bn o M Lai v Thi Lan c cng chung ngun gc. Cc khu h c ny pht sinh dc theo b bin ng Dng trong iu kin nc bin ca vng c lm nht bi mt khi lng ln nc ngt ca cc sng vng ny. V vy, khu h c nc ngt min Nam (lu vc sng Cu Long v sng ng Nai) cn c xp chung n v a l phn b c phn vng vi M Lai, Thi Lan v Indonexia [19]. Cc tc gi ny chia cc thy vc nc ngt ca Vit Nam ra lm 11 khu (n v) a l ng vt thuc 2 tnh a ng vt tnh Bc Vit Nam - Hoa Nam v tnh ng Dng. Tnh a ng vt Bc Vit Nam - Hoa Nam thuc phn vng Trung Hoa v tnh a ng vt ng Dng thuc phn vng a l ng vt n - Malayxia (bng 2.2, hnh 2.7) [3], [7], [8], [10], [15, 16, 18, 20]. Nh vy, chng ta thy rng c nhiu quan im phn chia vng a ng vt c nc ngt. Ni v v tr ca khu h c Vit Nam phi khng nh n nm trong vng ng phng (Oriental) hay cn gi l vng Trung - n (Indo-chinese). Vng ny theo Berg L. S. (1933, 1948, 1949) c 3 phn vng:

1. Phn vng A Mua; 2. Phn vng Trung Hoa: t gii hn pha Nam ca phn vng Amua ti lu vcsng Ty Giang;

3. Phn vng n bao gm ng Dng, n , qun o M Lai, pha ngt ng gianh gii Wallacea. Theo Starobogatov J. I. (1970) vng ny c 3 phn vng:

1. Phn vng Amua - Nht Bn.2. Phn vng Trung Hoa vi 5 tnh a ng vt:

2.1 Tnh Hong H; 2.2 Tnh Trng Giang; 2.3 Tnh Hoa Nam; 2.4 Tnh Vn Nam;

44

2.5 Tnh Bc Vit Nam; 3. Phn vng n - M Lai vi 8 tnh a ng vt: 3.1 Tnh Mekong (Nam Vit Nam, Lo, ng Bc Thi Lan, Campuchia); 3.2 Tnh M Nam - M Lai; 3.3 Tnh Adaman; 3.4 Tnh Sumatra; 3.5 Tnh Java; 3.6 Tnh Sn nh; 3.7 Tnh Kalimantan; 3.8 Tnh Sulavsi.Theo Bnrescu (1964) vng ny c 4 phn vng:

1. Phn vng ng (Trung Hoa); 2. Phn vng n - M Lai; 3. Phn vng Ty ;4. Phn vng min ni chu . Theo ng Ngc Thanh (1980) vng ny c cc phn vng sau:

1. Phn vng Amua;2. Phn vng Trung Hoa: gii hn t lu vc sng Hong H ti lu vc sng Trng Giang. Phn vng ny c 3 tnh:

2.1 Tnh Hong H: gii hn ti pha Nam sng Hong H; 2.2 Tnh Trng Giang: gii hn ti gia Trng Giang v Ty Giang; 2.3 Tnh Vn Nam: tp hp loi Vn Nam.3. Phn vng Bc Vit Nam - Hoa Nam mang tnh chuyn tip ca 2 phn vng Trung Hoa v phn vng n - M Lai. Gii hn t lu vc sng Ty Giang (pha Nam dy Nam Lnh) ti lu vc sng Hng - sng C (pha ng v Bc Trng Sn) tp hp loi hn hp vi cc yu t Trung Hoa v n - M Lai. Tnh cht c lp ca Bc Vit Nam i vi cc khu vc phn chia a sinh vt hc ln cn da trn cc c s sau y [14]:

45 - Bc Vit Nam nm trong khu vc ranh gii phn b tp hp loi cn nhit i pha Bc v tp hp loi nhit i pha Nam, mang ngha chuyn tip. Nhng iu c bit khu vc chuyn tip ny a dng v thnh phn loi. - Bc Vit Nam c thnh phn loi c hu cao c v c hu cng nh v bc c hu. Mc c hu cao ca khu h ng vt nc ngt Bc Vit Nam th hin tnh cht c trng ca vng ny so vi cc vng k cn. - V mt iu kin t nhin c th thy s khc bit ca h thng sng Hng, sng , sng M, sng C Bc Vit Nam vi h thng sng M Kng pha nam bn o ng Dng. - Tch vng pha Bc Vit Nam thnh mt n v a ng vt hc c lp vi phn vng Trung Hoa v phn vng n -M Lai cng ph hp vi ch kh hu c trng ca vng ny. Ch kh hu min Bc Vit Nam mang tnh cht nhit i m gi ma, nhng c ma ng lnh ko di t thng XI n thng III nm sau. C th coi ch nhit ca cc thy vc ny nh mt dng chuyn tip gia ch nhit cc thy vc ni a vng nhit i in hnh pha nam khng c trng thi lnh dic 200C hng nm vi ch nhit cc thy vc vng cn nhit i c trng thi lnh di 50C hng nm. Phn vng c 2 tnh:

2.4 Tnh Hoa Nam: gm Trung v h lu sng Ty Giang. Tp hp loi chu ca vng ny, c rt t yu t n - M Lai.

2.5 Tnh Bc Vit Nam: Trung v h lu cc sng Hng, sng , sng M,sng C, cc sng sn ng Trng Sn v Bc Trung B cho ti o Hi Vn vi thnh phn loi c hu ca vng. Yu t n - M cn phong ph ngang vi yu t Trung Hoa. y l vng phn b thp nht v pha Nam ca cc loi n i v cn nhit i. Nh vy, khu h c nc ngt Vit Nam c phn chia nh sau (Bng 2.2):

46

Bng 2.2. Vng a l ng vt hc khu h c nc ngt Vit Nam (vng ng Phng) Khu h c nc ngt Vit Nam Phn vng 1 Phn vng Trung Hoa 2 3 4 5 10 Khu a l (n v a l phn b c) Cao Lng Vit Bc Ty Bc Min ni Bc Trung B ng bng Bc B v Bc Trung B S loi c [4,5,6] 104 226 192 372 316

Vng chuyn tip

Trung v Nam Trung B mang tnh 251 cht chuyn tip theo hng Bc Nam in Bin Ph mang tnh cht 110 chuyn tip theo hng Ty Bc Ty Nguyn H lu sng Mekong ng bng Nam B o Ph Quc 189

11 6 Phn vng n Malayxia 7 8 9

a. Phn vng Trung Hoa [8], [19] - Gii hn: cn c vo mc ging nhau v thnh phn loi, khu h c nc ngt min Bc Vit Nam c quan h gn vi khu h c nc ngt Nam Trung Hoa, rt xa vi khu h c nc ngt ng Dng, v do Bc Vit Nam c xp vo tnh Hoa Nam - Bc Vit Nam, bao gm tt c cc h sng sui Min Bc Vit Nam v pha nam n sng La. - V thnh phn loi: khu h c nc ngt min Bc Vit Nam a dng v thnh phn loi, c 203 loi thuc 114 ging, 27 h; cc h c nhiu loi theo th t l h c Chp Cyprinidae (110 loi), h c Chch vy bng Balitoridae (10 loi), h c Lng Bagridae (10 loi), h c Bng trng Gobiidae (9 loi), h c Nheo Siluridae (9 loi). S lng cc loi c hu kh cao (hn 60 loi), c 11 loi chung vi khu h c nc ngt min Nam [18].

47 - V phn chia khu a l: khu h c nc ngt min Bc Vit Nam c th chia ra 5 n v a l phn b c khc nhau: 1) Khu Cao Bng - Lng Sn, 2) Khu Vit Bc, 3) Khu Ty Bc, 4) Khu min ni Bc Trng Sn, 5) Khu ng bng Bc B v Bc Trung B (bng 2.2).

XI

Hnh 2.7. S phn b vng a l ng vt hc khu h c nc ngt Vit Nam (Theo Mai nh Yn v Nguyn Hu Dc (1995), Nguyn Vn Ho (1998)I, II, III. IV, V. Phn vng Trung Hoa; VI, VII, VIII, IX. Phn vng n - M Lai; X, XI. Khu phn b chuyn tip.

- V nhm sinh thi c: khu h c Min Bc c th chia ra 2 nhm sinh thi r rng: nhm c min ni: 4 khu v nhm c ng bng: 1 khu. V c im sinh hc,

48 khu h c nc ngt min Bc Vit Nam phn nh tnh cht ca sinh vt vng nhit i c gi ma [19].

Bng 2.2. n v a l phn b c H thng sng thuc khu h c nc ngt min Bc Vit Nam TT 1 n v a l phn b c Khu Cao Bng - Lng Sn H thng sng Sng K Cng - Bng (Lng Sn Cao Bng) chy t Vit Nam sang Trung Quc hp thnh T Giang chy vo Ty Giang Sng Hng: sng Chy, sng L, sng Gm, Ph y Sng , sng M Sng C Sng Thi Bnh, H lu cc sng Hng, sng M, sng C.

2 3 4 5

Khu Vit Bc Khu Ty Bc Khu min ni Bc Trng Sn Khu ng bng Bc B v Bc Trung B b. Phn vng n - M Lai [8], [19]

- Gii hn: khu h c nc ngt min Nam Vit Nam v c Campuchia rt ging vi khu h c Indonexia, khc vi n v Myanma, theo H. M. Smith (1945) Cc khu h c Indonexia, ng Dng, bn o Malayxia v Thi Lan c cng ngun gc. Cc khu h c ny pht sinh dc theo b bin ng Dng trong iu kin nc bin ca vng c lm nht bi mt khi lng ln nc ngt ca cc sng trong vng ny. Do khu h c nc ngt min Nam l mt phn ca phn min ng Dng hay Mekong, bao gm ng bng sng Mekong, b bin min Nam v h thng sng cao nguyn Ty Nguyn vo sng Mekong. - V thnh phn loi: i b phn l cc c sng vng ng bng, rt nhiu loi c nc l. Vn c s t c min ni sng cc sui nc chy. Khu h c nc ngt min Nam Vit Nam a dng v thnh phn loi, c 255 loi c thuc 130 ging, 43 h. Trong thnh phn, i b phn l cc loi c sng vng ng bng, rt nhiu loi c nc l, vn c mt s c min ni sng cc sui nc chy. Cc h c nhiu loi xp theo th t c h c Chp Cyprinidae, h c Lng Bargridae, h c Nheo

49 Siluridae, h c Lc (h c Qu) Channidae, h c R ng Anabantidae, h c Chch sng Mastacembelidae. Nhng loi c nc ngt c coi l c kinh t nh cc ging v loi: c L tre (Parahela), c Lng tong (Rasbora), c Linh bng (Thynnichthys), c Li (Osteochilus), c Cc (Cyclocheilichthys), c Dnh (Puntioplites), c Ta tri (Labeo) thuc h c Chp Cyprinidae; c Tr (Clarias) thuc h c Tr Clariidae; thuc h c Chin Sisoridae c c Leo (Wallago attu), h c Tra Pangarisdae c c Tra (Pangasius), h c Lng Bagridae c c Cht (Mystus); h c Lc Channidae c c Lc ng (Channa striata), c Lc bng (Channa micropeltes); h c R ng (Anabantidae) c c Sc (Trichopteus) [20]. - V phn chia khu a l: khu h c nc ngt min Nam Vit Nam c th c chia ra 4 n v a l phn b c khc nhau: 1) Khu cao nguyn Ty Nguyn, 2) Khu lu vc sng ng Nai, 3) Khu ng bng Nam B, 4) Khu o Ph Quc (bng 2.3). - V nhm sinh thi c: khu h c nc ngt min Nam c th chia ra hai nhm sinh thi: nhm c min ni hai khu v nhm c ng bng 2 khu. Bng 2.3. n v a l phn b c H thng sng thuc khu h c nc ngt min Nam Vit Nam TT 1 2 3 4 n v a l phn b c Khu cao nguyn Ty Nguyn Khu lu vc sng ng Nai Khu ng bng Nam B Khu o Ph Quc c. Khu vc chuyn tip - Khu vc chuyn tip min Trung: cc h sng ca b bin min Trung t sng La tnh Ngh An n sng Ci tnh Khnh Ha l cc sng ngn vi thnh phn khu h c hn hp ch yu l c nc l, mt s t c nc ngt, chuyn tip ca hai khu h c nc ngt min Bc thuc phn min Nam Trung Hoa v min Nam thuc phn min ng Dng. Ton b khu vc ny hnh thnh mt n v a l ng vt c nc ngt ring - khu vc chuyn tip theo hng Bc Nam [3]. H thng sng Sng Sesan, sng Ba, sng sui Ty Nguyn Sng ng Nai, sng La Ng, sng B, sng Si Gn Sng Tin, sng Hu, sng Vm C ng, sng Vm C Ty, sng Cu Long

50 - Khu vc chuyn tip in Bin Ph: cc sng sui thuc lu vc sng Nm Rm (chi lu ca sng Mekong), tnh in Bin mang tnh cht chuyn tip theo hng Ty Bc.

51 TI LIU THAM KHO

1. B Gio dc v o to (2007), Tp bn th gii v cc chu lc, Nxb Giodc, H Ni.

2. B Thy sn (1996), Ngun li thy sn Vit Nam, Nxb Nng nghip, H Ni,616 tr.

3. Nguyn Hu Dc (1995), Gp phn nghin cu khu h c nc ngt Nam TrungB Vit Nam, Lun n ph tin s khoa hc Sinh hc, Trng i hc S phm H Ni, 183 tr.

4. Nguyn Vn Ho (ch bin), Ng S Vn (2001), C nc ngt Vit Nam, H cChp (Cyprinidae), Tp I, Nxb Nng nghip, H Ni, 622 tr.

5. Nguyn Vn Ho (2005), C nc ngt Vit Nam, Lp c Sn v bn lin b canhm c Xng (lin b c Tht lt, lin b c dng Trch, tng b c dng Cho v lin b c dng Chp), Tp II, Nxb Nng nghip, H Ni, 760 tr.

6. Nguyn Vn Ho (2005), C nc ngt Vit Nam, Ba lin b ca lp c Xng(lin b c dng Mang ch, lin b c dng Sut v lin b c dng Vc), Tp III, Nxb Nng nghip, H Ni, 759 tr.

7. Nguyn Th Thu H (2001), iu tra khu h c ca mt s sng sui TyNguyn, Lun n tin s Sinh hc, Trng i hc Khoa hc T nhin, i hc Quc gia H Ni, 148 tr.

8. L V Khi, Nguyn Ngha Thn (2001), a l sinh vt, Nxb i hc Quc giaH Ni, 171 tr.

9. Trn Kin (ch bin), Trn Hng Vit (2003), ng vt c xng sng, Tp I,C v Lng c, Nxb i hc S phm H Ni, tr. 1-197, 522 tr.

10. Dng Quang Ngc (2007), Gp phn nghin cu c lu vc sng M thuca phn Vit Nam, Lun n tin s khoa hc Sinh hc, Trng i hc S phm H Ni, 159 tr.

11. Nh xut bn Bn (2008), Tp bn hnh chnh 64 tnh, thnh ph VitNam, Ti bn ln th hai, Nxb Bn , 121 tr.

12. Ptrov O. V. (1959), Gio trnh a ng vt hc, L Cm Thch dch, Trngi hc Tng hp H Ni (Trng H Khoa hc T nhin H Ni), 338 tr.

52

13. V Trung Tng (2009), Cc h sinh thi ca sng Vit Nam (Khai thc, duy trv pht trin ngun li), Nxb Khoa hc v K thut, H Ni, 271 tr.

14. ng Ngc Thanh, H Thanh Hi (2007), C s thy sinh hc, Nxb Khoa hcT nhin v Cng ngh, tr. 261-282.

15. Nguyn Thi T (1983), Khu h c lu vc sng Lam, Lun n ph tin s Sinhhc, Trng i hc Tng hp H Ni, 179 tr.

16. Nguyn Thi T v cng s (2003), Min Trung Vit Nam vi a ng vtc nc ngt, Tuyn tp bo co khoa hc v nui trng thy sn, Nxb Nng nghip, tr. 527-530.

17. Voronov A. G. (1976), a l sinh vt, ng Ngc Ln dch, Nxb Khoa hc vK thut, H Ni, 334 tr.

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19. Mai nh Yn, V Trung Tng, Bi Lai, Trn Mai Thin (1979), Ng loi hc,Nxb i hc v Trung hc chuyn nghip, H Ni, 385 tr.

20. Mai nh Yn (ch bin), Nguyn Vn Trng, Nguyn Vn Thin, L HongYn, Ha Bch Loan (1992), nh loi cc loi c nc ngt Nam B, Nxb Khoa hc v K thut, H Ni, 351 tr.

21. http://www.fao.org