Chapter 9 Fishes

Introduction to the Freshwater Fishes

J. S. Sparks and M. L. J . .Stiassny

Alrhough many of Madagascar's rcrrestrial vertebrares have been studied in great decail, parricularly the lemurs, very little up-to-date information is availa ble for the highly threatened freshwater fishes native to the island. This intro­duction provides a summary of Madagascar's native fresh­water fishes and an update on the current state of knowl­edgc regarding the origins, composition, biogeography, and relationships of this ali but neglected vertebratc buna. We do not attempt a summary of the hydrology, limnology, or conservation status of Madagascar's aquaric resources here, as these have bcen presented in detail elsewhere (e.g., Battistini and Richard-Vindard 1972; Chaperon et al. 1993; Riseng 1997; Wright 1997; Benstead et al. 2000). Herein wc focus on patterns of fish diversity and distribu­tion and the historical geological events that have shaped them.

To interpret the origin(s) and current composition of the ichthyofauna in a useful way, we need not only information on the phylogenetic affinities of the groups present but also knowledge of their distributions in spa ce and ti me. We sum­marize both historical and recent survey data and attempt to synthesize these and current phylogenetic hypotheses in order to provide a contextual overview of the island's fresh­water fish faur}a. Comrary to a commonly expressed belief (e.g., Grandidier and Petit 1932), Madagascar's freshwater fishes are not well known, and phylogenetic relationships of only a few groups have been investigated to date. We docu­ment this low leve! of knowledge and discuss possible rea­sons for it, as weil as how our understanding of this fauna has advanced over the past decade and where gaps in

849

knowledge persist. Finally, in the face of the current rate of aquatic habitat degradation in M·adagascar, we present our vicw of the future of the island's freshwater ichthyofauna.

In many ways Madagascar possesses a typical island ichthyofauna, but it is also one that differs in certain re­spects because of its continemal (Gondwanan) origin. Like those of many true oceanic islands, Madagascar's na­tive ichthyofauna is relatively depauperate at broad taxo­nomie levels when compared with those of much larger, geogmphically more diverse continentallandmasses (table 9.1). However, bascd on the revised totals presented herein and considering the surface arca of the island, the notion of a depauperate ichthyofauna at the species leve! for Mada­gascar is no longer tenable (e.g., Kiener 1963; Kiener and Richard-Vindard 1972; Jenkins 1987). In fact, Madagas­car's freshwarer fish fauna is shown to be numerically fully in line with those of other landmasses of similar size and supports more or Jess cxacdy as many species as would be predicted given the island's surface area of nearly 600,000 km2 (fig. 9.1; MacArthur and Wilson 1967; Brown and Lomolino 1998).

In contrast to many othee island systems and owing ro its continental origin, Madagascar, isolated since. the Creta­ceous (Storey 1995; Hay et al. 1999), is home to small radi­ations of freshwater fishes thar do not readily enter marine habitats. Many taxonomie groups with members present on the island have broad Gondwanan distributions and rhus rich potential to provide insighr into the past connec­tions of the southern continents. In sharp contrast, othee islands of the region, such as the Comoro Islands and

850 Fishes Introduction

10000 w

1000 IS ... 1

l a:

10 ..

t "'

100

! $1. cu Il NZ MDl

10

..

10' 10' ,,. 10' ,,. At•• (km')

Figure 9. 1. Species-area relatiooships for the reported number of native fresh­water fish species from MadagaS(ar and ether continental and oceanic land­masses (modified alter Riseng 1997). Relationships are shown indicating the in­crease in the number of freshwater fish species recorded from the fresh waters of Madagascar over the past three decades (symbols MO 1-MD4). Totals for Mada­gascar are shown correspondin<) to the number of native freshwater species re­ported in this study (MD• •: 143 spp.); the number of endemie freshwater spedes recorded in this study (MOe: 93 spp.); and the number of endemie species re­corded by Kiener and Maugé {1972, MOt: 32 spp.), Stiassny and Raminosoa (1994, M02: 42 spp.), de Rham (1996, M03: 49 spp.). and Benstead et al. (2000, M04: 58 spp.). Abbreviations (references for species tetais used to compile this figure Jisted in parentheses): Af = Al rica (Caget et al. 1984, 1986; Skelton 1990; lundberg et al. 2000); AS .. Australia (Allen 1989; Pellard et al. 1990; McOowall 1996); B = Bornee (M. Kottelat (pers. comm.l records 394 species from Bornee (shown] and estimates that there are now approximately 450 described species (not shownJ; Inger and Kong(1962] report 290 species from western Bornee (not shownD; CU-= Cuba (SS(shownl recorded by Alayo (19731 and 36(not shawn} by Vergara (1980}); Hl = Hawaii (Fitzsimons and Nishimoto 1990); lM = Inde­Malay archipelago (Zakaria-lsmail 1994 (minimum estimateJ; Kottelat {19981 states that approximately 1000 species are known from western lndonesia (not shawn)); IS = lndian subcontinent (Ta lw ar and Jhingran 1992); NA= North Amer­ica (Williams and Miller 1990; lundberg et al. 2000); NG = New Guinea (Munro 1967; Allen [ 1991 J records 320-350 species including sorne estuarine forms (not shownlJ; NZ =New Zealand (McOowall 1990); SA ~ South America (Moyle and Cech 1996; Vari and Malabarba 1998); SL =Sri Lanka (Pethiyagoda 1991); and w = wocld (Stiassny 1996; Lundberg et al. 2000). Geographie areas obtained from Rand McNally Universal World Atlas (1987) .•

Mascarenes (which are of recent volcanic origin, 15 million years ago [Ma] or less) and the granitic Seychelles (ancient Gondwanan fragments isolated since approximately the Late Cretaceous [Plummer and Belle 1995; Storey 1995]), have extremely depauperate fish faunas dominated by ma­rine colonizers or species with !ife histories dependent on marine habitats, such as gobies, eleotrids, ambassids, eels, and mullets (Bennett 1830; Bleeker and Pollen 1875; Teugels et al. 1985).

An extensive literature on Madagascar's freshwater fishes datesfrom the mid-1800s (e.g., Bleeker 1868; Bleeker and Pollen 1875; Sauvage 1891; Grandidier and Petit 1932; Pellegrin 1933; Bertin 1948; Arnoult 1959; Kiener 1963,

1965; Kiener and Maugé 1966; Kiener and Richard­Vindard 1972), and by the carly part of the past cenrury most biologists had concluded chat the ichthyofauna of Madagascar was weil known (e.g., Grandidier and Petit 1932). However, beyond lists of species known at the time, for the most part little additional information on the is­land's fishes was reported in this literature. Notably lacking was information on !ife history, reproductive biology, and relationships of the native fishes and their patterns of dis­tribution both within Madagascar and regionally. ln fact, despite a literature going back 150 years, it is remarkable how little we still know about the majority of Madagascar's freshwater fishes .

Perhaps as a result of this lack of knowledge, Madagas­car's fishes have not been a mainstream focus for efforts of conservation organizations or government agencies, and in the design of protected areas native fishes have traditionally been neglected. Furthermore, larger rivees are frequently used as reserve boundaries, which does little to prorect the integrity of the river itself. An exemplary exception is the recendy designated Parc National (PN) de Masoala in northeastern Madagascar (Kremen et al. 1999). The PN de Masoala was designed to indude river basins within its bor­ders specifically to protect native fish communities. Possibly another reason for a continued terres trial bias is the sad fact that today few areas of the island remain where intact na­tive fish communities persist. Exotic species, especially eila· piine cichlids introduced for aquaculture purposes, are ubiquitous in ali but the most remote regions of the island (j. Sparks and K. Riseng unpubl. data), and the degree of habitat degradation and destruction in Madagascar has been, and continues to be, severe (Benstead et al. 2000).

The paucity of information on Madagascar's freshwater fishes, and the Jack of consideration they have received from conservationists, are certainly also attributable to the inac­cessibility of many of the island's river basins and the dif­ficulties associated with the conservation of river systems in general (Boon et al. 2000). Most of Madagascar's protected areas are very small, frequenrly consisting only of a small forest fragment surrounded by an expansive deforested re­gion. Under such circumstances, at very best only a few headwater streams can be afforded any protection. Unfor­tunately, headwater regions do not harbor diverse fish as­semblages and as such are not the habitats most în need of protection from the perspective of maintaining ichthyolog­ical diversity.

lt has long been recognized that Madagascar is charac­terized by a highly endemie freshwater ichthyofauna, but historically this fauna has been viewed as notably species­poor. Calculations based on prior estimates of species rich­ness suggested that Madagascar was home to only about

J. S. Sparks and M. l. J. Stiassny 851

Table 9. 1. Checklist of native Malagasy freshwater flshes and their regions of occurrence

Conservation Southern Western Northwestern Eastern Eastern Taxon status basins basins basins highlands lowlands

Anguillidae Anguilla bicolor s x x x x x A. marmorata s x x x x x A. mossambka s x x x x x

Clupeidae Pellona ditche!a u x x x Sauvage/fa madagascariensis s x x x S. nov. sp. *robustaH u x Spratellomorpha bianafis u x x

Ariidae Arius afrkanus s x x x A. dussumieri u x x A. madagascarlensis T x x A. nov. sp. *ankofia* T x A. nov. sp. *sofia• u x

Anchariidae Ancharlus brevibarbus TIR x x A. fuscus T/R x x A. nov. sp. ·southwestH R x A. nov. sp. *southeast * R x

Atherinidae Atherinomoros d . duodecimalis s x x x Teramulus klenerl R/E? x T. waterloti R x

Bedotiidae Sedotia geay/ T x B. madagascariensis T x B. /ongianalis T x B. marojejy T x B.masoala T x B. tricolor T x B.vondrozo T x B. nov. sp. "bemarivo .. T x B. nov. sp. *betampona* T x x B. nov. sp. *garassa • T

B. nov. sp. */azana• T x B. nov. sp. *mahanara• T x B. nov. sp. *manomboH T/R x B. nov. sp. *marosivy• T x x B. nov. sp. *nosivoloH T x B. nov. sp. * ranomafana• T x B. nov. sp. *sambava" T

Rheocles a/aotrensis T x R. derhami u x R. larera/is T x R. pellegrini R) x R. sikorae E? x R. wrightae RIE' x R. nov. sp. *ambatovy• TIR x R. nov. sp. *andapaH u x R. nov. sp. *rlanfla• u x

(continuee/)

852 Fishes Introduction

Table 9.1. (cootinued)

Conservation Southern Western Northwestern Eastern Eastern Taxon status basins basins basins highlands lowlands

Aplocheilidae Pachypanchax sakaramyi T x P. omalonotus T x P. nov. sp. •anjingo• T x P. nov. sp. •betslboka• T x P. nov. sp. •manambery• T

P. nov. sp. •sofia• TIR x Poec~iidae Pantanodon madagascariensis x

P. nov. sp. •manombo• RIE? x Syngnathidae Coelonotus leiaspis u x x x

Hippichthys cyanospilus u x x x MICJOPhis brachyurus s x M. fluviatilis s x x x

Ambassidae Ambassis fontoynonti T

A natalensis s x x x x A. productus s - x x x x

Terapontidae Terapon jarbua s x x x Mesopristes elongatus u x x

Kuhliidae Kuhlia rupestris s x x x x Monodactytidae Monodactylus argenteus s x x x Scatophagidae Scatophagus tetracanthus s x x x Carangidae Caranx sexfasciatus s x x x Chanidae Chanos chanos u x x x C ichlidae Paratilapla pol/eni T x x x x

P. bleekeri T x x x P. nov. sp. •al/ black• R x P. nov. sp. •fony• T x P. nov. sp. •;hotry• E? x Ptychochromis grandidieri s x P. oligacanthus T x x x x P. nov. sp. •btack saroy• u P. nov. sp. •green garaka• u x x P. nov. sp. •fnornatus• R x x P. nov. sp. •kotrolonili•hy• E? x P. nov. sp. •mipentina• u x P. nov. sp. •nossibeensis• T x x Ptychochromoides betsileanus R x P. katria R x P. vondrozo R x P. nov. sp. •jtasy" x Oxylapia po/li R x Paretroplus damii T x P. kieneri T/R x x P. maculatus TIR x P. maromandia R x x P. menarambo R/E1 x P. nourissati T x

J. S. Sparks and M. L. J. Stiassny 853

T.,ble 9.1. (continued)

Conservation Southern Western Northwestern Eastern Eastern Taxon status basins basins basins highlands lowlands

P. petit/ R? x P.polyadlr s x x P. nov. sp. •anlcarafantslkèf• T x x P. nov. sp. ·dambabe• T x P. nov. sp. •dridrimena• T x P. nov. sp. •tac parinadrina• T x P. nov. sp. •sofia• T/R x P. nov. sp. •tsimoty• T x P. nov. sp. •ventitry• T

Mugilidae Agonostomus telfairii T x Uza rnacrolepis u x x x L. alata u x x x Mugit cephalus u x x Valamugil buchanani u x x x V. tobustus u x x

Gobiidae Acenuogobius audax u x x x A therezieni u x Awaous aeneofuscus s x x x Chonophorus macrorhynchu$ u x x Glossogobius bioceRiJtus u x x G. giuris s x x x x

G. ankaranensis T x x

G. callidus u x x Gobius hypselosoma u x x &uhygobius sambiranoensis u x B. fuscus u x tstigobius omiJtuS u x x x 0/igotepis iJCutipennis u Oxyurichthys tentaculatis u x x x Popif/ogobius reichei u x x x Redigobius balteiltops u x

R. bikofilnus · u x

Sicyopterus laticeps T x x S. franouxi T x x S. nov. sp. •masoala• T x x

Stenogobius genivittatus u x x x Taenioides gracilis u x

Yongeichthys nebulosus u x x x Eleotridae Butis butis s x x x

Eleotris acanthopoma u x

f . fusca 5 x x x x

E. melanosoma u x x E. pel/egrini u x x E. vomerodentata u x Hypse/eotris tohizonae u x x

(continued)

854 Fishes Introduction

Table 9.1. Ccom.nued)

Conservation Southern Western Northwestern Eastern Eastern Taxon status basins basins basins highlands lowlands

Ophiocara porocl!phala u x x x O. macrol!!pidora u x x Ratslrakia J~gendrei T x x Typhleotris madagascariensis R x T. pauliani R x T. nov. sp. ~anomafy" R x

Megalopidae Megalops cyprinoides s x x Totals' 10 49 71 51 69 .

NOTES: The live major ecoregions listed correspond tc those discussed in the te~t. Families. genera, or species in boldface typl! are endemie tc Madagascar. Conse..Va­tion status abbreviations: S. se<ure; u. unknown; T. threatened: R. extremely rare/highly endangered; E, presumed exllnct. An x indicates presence of a species in a particular e<oregion. Undescribed spe<ies are designated by • nov. sp. •

•There are 21 families (2 endemie). 54 genera (14 endemie), and 143 species (93 endemie). The sum of the columns is more than the total number of species because sorne species inhabit more than one e<oregion.

30% of its predicted freshwarer fish diversity, based on a surface area of nearly 600,000 km! (Riseng 1997). In con­trasr, the summary presented here brings Malagasy fresh­water fish species diversity completely into line with those of other land masses of comparable size (fig. 9 .1, table 9.1 ). Whereas our new findings are satisfying from a rheoretical standpoint, they are disheanening from one of conserva­tion. The combined pressures of human encroachmenr, de­forestation, overfishing, and the introduction of a wide va­riety of exotic species are having a major impact on native fish populations (Stiassny and Raminosoa 1994; Benstead et al. 2000). Numerous species, including a number of un­described taxa, are recognized as extremely endangered or verging on extinction or both (table 9.1; Harrison and Stiassny 1999; Benstead et al. 2000). Although infrequently discussed in the conservation literature, many of Madagas­car's endemie freshwatcr fishes likely represent sorne of the most, if not the most, endangered vertebrates on the island (Sriassny and Raminosoa 1994; Wright 1997; Sparks and Stiassny in press).

Globally, freshwater systems are often overlooked in the preparation of conservation protocols, and Madagascar has been no exception to this bias. This is a remarkable oversight when one considers thar freshwater fishes alone account for an astounding 20-25% of the world's verte­brate dh·ersity (Stiassny and Raminosoa 1994; Lundberg et al. 2000). Few pa pers have dealt specifically with the con· servation of Madagascar's freshwater fishes (e.g., Reinthal and Stiassny 1991_; Stiassny and Raminosoa 1994; Sparks and Stiassny in press), yet the entire Malagasy freshwater ichthyofauna, and aquatic systems of the island in general (Riseng 1997), are in serious trouble. Extremely few fresh-

water habitats remain throughout Madagascar that are not highly disturbed, degraded, and dominated hy exotic spe­cies (fig. 9.2).

?\·tost summary works on Malagasy freshwater fishes are now outdated (e.g., Blcekcr and Pollen 1 875; Sauvage 1891; Pellcgrin 1933; Arnoult 1959; Kiener 1963; Kiencr and Richard-Vindard 1972; Stiassny and Raminosoa 1994; de Rham 1996) or self-admittedly incomplete and cursory (jcnkins 1987; Glaw and Vences 1994 ). Most edited com­pilations dealing with "cntire" Malagasy faunas have failed to include consideration of fishes or aquatic systems in gen­eral. Happily, there are recent indications of change (see, e.g., Goodman 2000; part 9 of this volume), and as an en­couragement to such inclusion we fee! it timely to reevalu­ate the starus of Madagascar's freshwater fishes. The results presented in this chapter represent a decade of surveys conductcd across the island, as well as revisional works on a numbcr of fish groups. Many colleagues have graciously made their specimens and collection data available to us, and we have attempted to incorporate as much information as possible into this summary.

Species lnventory

We have fairly comprehensive survey coverage of the island, less a few critical regions in dire need of exploration (fig. 9.3A: shaded regions). In particular, we Jack data for west­ern Madagascar to the south and west of the Mahavavy du Sud Basin, the remote forested regions of the eastern and western highlands extending from Mandritsara south to Lac Alaotra (including headwaters of both eastern and

Figur~ 9.2. Pristlne and moderately disturbed freshwater hab1· tats: (A) A pristine rain forest stream in northeastern Madagascar (Ankavanana River, Masoala Peninsula). (B) A moderately dis· turbed river in northwestern Madagascar (Anjingo River. Ankofia drainage, near Antsohihy). (C) A typical highly disturbed lacus­trine freshwater habitat in north~.WStern Madagascar (Lac Rave­lobe near the Station forestière d'Ampijoroa) thal has been con­verted for rice cultivation and grazing of livestock. (0) A highly disturbed riverine habitat in the central highlands. upper Man­goro drainage east of Antananarivo.

856 Fishes Introduction

A

B Westem Sediment81)'

Plain

Ea<tem Escatpment

Figure 9.3. (A) Five major hydrographie ecoregions recognized in this study, comprising the pastprn highlands and lowlands, the western basins, the rivers and lakes of northwestern Madagascar. and the southern headwaters. The figures in boxes indicate the total number of native freshwater species (- spp.) recorded from the particular ecoregion and the number of those species endemie ( = eer) to that particular eco region. Shading indicates areas in need of additional ichthyo­faunal survey. (8) Cross-sectional relief map of Madagascar, illustrating the wide western plain and narrow. steep eastern escarpment.

western drainages encompassed by this region, e.g., of the Sofia, Mahajamba, Kamoro, Betsiboka, Rantabe, and Ma­rimbona Rivers), the headwaters of the Tsaratanana Massif in the north, and the forested regions of the southeastern highlands (especially south of the Mananara drainage ba­sin) (fig. 9.3A).

With few except ions, species listed in table 9.1 that were not collected persona li y or by collaborators (i.e., those listed in recent global compendiums such as Daget et aL 1984, 1986; Eschmeyer 1998) have been verified by examination of existing museum collections. Our main concern was to compile an accurare, up-to-date list of the native fishes in­habiting the inland waters of Madagascar. Our aim was to be as conserva rive as possible but to re present full y the true ichthyofaunal diversity on the island. Several species have not been collected in recent years, and for these we relied on museum records and specimens to verify their occur-

renee. This approach has resulted in the elimination from table 9.1 of certain species historically reported to occur in Madagascar, such as Sicyopterus lagocephalus, S. (1.1sciatus, and Kuhlia caudivittata, for which we were unable to ver­ify a record of occurrence on che island. The attribution of rhese species, and certain others, to Malagasy inland waters is the result of either taxonomie misidentification or incor­rectly reported locality data. Given that Madagascar's fresh­water fishes have traditionally been poorly studied, many unique endemie species have erroneously been anributed ro nominal species that do noe occur anywhere within che Mascarene region (also induding the Comoro Islands, the islands of La Réunion, Mauritius, and Rodrigues, and the Seychelles Islands). Further, wc have rectified severa! taxonomic/species misidenrifications thar had persisted in the literature.

Table 9.1 includes a number of undescribed species, ali of which we have examined ro confirm their taxonomie sta­tus. Inclusion of these novel taxa is not only justified but also necessary for an accurate representation of ichthyofau­nal diversity, and many are in the process of being dcscribed (e.g., Sparks 200la, 2002, in press; Sparks and Reinrhal 2001; Stiassny and Rodriguez 2001; Stiassny et al. 2001; Stiassny 2002), and severa! more await description (loiselle and Rodriguez in prep.; Sparks and Nelson in prep.). The large number of undescribed species results in part from in­tensive collecting efforts during the past decade, often fo­cusing on remote a reas of the island-such as the :Vtasoala Peninsula, headwater regions in the norrhwest, eastern and western basins of the southern highlands nea r Andringitra, and northeastern drainages-thar were previously unsur­veyed. The great majority of undescribed species are mem­bers of the Bedotiidae and Cichlidae, reflecting in part a greater taxonomie discrimination, as these are the only two groups of Malagasy freshwater fishes that have been subject to recent revisional study (e.g., Stiassny 1990; Reinthal and Sriassny 1997; Sparks and Reinthal 1999, 2001; Sparks 2001 b, 2002; Stiassny et aL 2001 ).

Here we considera taxon as a "freshwater" species if ir is generally collected in, is commonly found weil inland in, oris restricted to completely freshwarer habitats. Following this definition we also include species whose life histories are poorly known but rhat appear to spend a significant portion of their li fe in fresh waters, as opposed to entering fresh water for the sole purpose of reproduction. Our in­terpretation errs on the conservarive side and may underes­timate the crue diversity of native Malagasy freshwater fish species. For example, we have not included severa! species of carangids (jacks), lutjanids (snappers), gerreids (mojar­ras), sparids (porgies), and haemulids (grunts), in addition to a .number of othee species belonging to marine familics

thar are frequently collecred weil inland and in freshwater habitats. Ir should be no ted rhat among ichthyologists rhere are differences in the definition of a "freshwater .. species, and lists vary somewhat in terms of the inclusion and ex­clusion of these taxa.

ln table 9.1 we list 143 native freshwarer species, be­longing to 21 families and 54 genera; 93 of rhese species (>65%) are endemie to Madagascar, whereas 99 species (>69%) are endemie to the Malagasy region (including Madagascar, the Comoro Islands, the Mascarene Islands of La Réunion, Mauritius, and Rodrigues, and the Seychelles). Malagasy freshwarer fish endemism is 60-90% greater than thar reporred in recent studies (table 9.1, fig. 9.1). For example, Kiener and Richard-Vindard (1972) recorded 32 endemie species, Stiassny and Raminosoa (1994) 42 spe· cies, and de Rham (1996) 49 species. Most recently Ben­stead er al. (2000) lise a tora! of 64 endemie species, of which 58 have been verified following our definition of freshwater taxa. This remarkable increase in the number of native freshwater fishes underscores the importance of continued efforts to collect in remere regions of the island. At higher taxonomie ranks endemism is muted, with only two en­demie families (9.5%) and 13 endemie genera (24.5%) recorded from the island (cable 9.1).

Hydrology and Fish Communities

Aldegheri ( 1972, p. 261) di vides Madagascar into five ma­jor hydrographie regions: the slopes of Montagne d'Ambre in· the far north, drainages of the Tsaratanana Massif in the north, eastern drainages, western and norchwcstern ba­sins, and southern basins. Although endemie fish species are found in each of thcse regions, we restricc our discus· sion to the regions with highcr ichthyofaunal diversity, in­cluding the eastern highlands and lowlands, the western ba ­sins, and the rivees and lakes of northwestern Madagascar (fig. 9.3A). These regions were not selected arbitrarily but conform to broad patterns of endemism.

Tradicionally, two major ichthyofaunal regions have beèn recognized: the east-coast drainages, with the high­est diversicy of freshwater fishes on the island (Kiener and Richard-Vindard 1972), a nd the much drier and suppos­edly species·poor western basins. East-coast drainages emp­tying into the Indian Ocean are characteristically steep with many rapids and cascades (fig. 9.2A). The rivers are shore and generally clcar and termina te on a ~arrow coastal plain over a narrow continental shelf. The sccep eastern slopes constitute approximately 25% of the total area of Mada­gascar (Aidegheri 1972; fig. 9 .3B) and are subject to high average annual rainfall. The headwaters of many eastern

J. S. Sparks and M. l. J. Stiassny 857

rivers have depauperate fish assemblages, frequently com­posed of only a few goby or eleotrid species (gobioids) or both. Eels (Anguilla spp.) are also present in these regions where there are no significant barriers to upstream dis­persal (i.e., waterfalls). According to Kiener (1963), only gobioids, eels, and the cichlids Paratilapia pol/eni and Ptychochrom"oides betsileanus have distributions extend­ing above 1000 rn, although in recent ichthyofaunal surveys neither of these genera has been found above 1000 m.

ln contrast, wesrern Madagascar is much drier (average annual rainfall is only about 25% th at of the eastern slopes) and characterized by longer, generally slow-flowing rivees subject to much seasonal fluctuation in water leve\ and flow rate (figs. 9.2B and 9.3B) and shallow, extremely turbid, oligorrophic floodplain lakes (fig. 9.2C). Many of the smaller river basins are dry from April to November {AI­degheri 1972). The rivers, and to a lesser extent also the lakes, of western coastal Madagascar are characterized by numerous intrusive marine species, many of which are fre­quently collected far inland (Kiener 1965}. This is largely due to an expansive continental shelf extending along most of the west coast and the presence of numerous coral reefs in the region with large fish populations (fig. 9.3B; Brenon 1972). Western rivers have significanr ridai influence in their lower reaches (Kiener and Richard-Vindard 1972), fa­cilitating colonization and recolonization by marine forms after periods of drought have extirpated freshwater species inhabiting these regions.

A significant result of the present study is the recognition of a second major region of ichchyofaunal diversity in Mad­agascar: the rivers and floodplain lakes of the northwest, and the subdivision of the eastern region, based on an ele­vational disjonction in species distribution, into the eastern highlands and lowlands (see also Sparks and Stiassny in press) (rable 9.1 and fig. 9.3A). A total of 71 native fresh­water species are recorded from northwesrern rivers and lakes, 69 species from the eastern lowlands, and 51 species from the eastern highlands (rable 9.1, fig. 9.3A). Fifty-seven native species have distributions restricted to eastern drainages, occurring in either the eastern highlands o r low­lands or both, whereas 48 native species are entirely re­stricted to western drainages. In their entirety, the eastern drainages therefore rep resent the most species-rich hydro­logie region of the island. However, if the upper and lower eastern basins are considered separately, as seems appro­priate given substantial differences in the fish assemblages present in each, the northwestern basins are the most spe· ciose and a Iso harbor rhe most species endemie to a partic­ular ecoregion (table 9.1, fig. 9.3A). Further, species diver­sity in the north west is likely underestimated, as a majority of the basins draining the Tsararanana Massif, as weil as a

858 Fishes Introduction

number of other basins in nonhwestern Madagascar, re­main unsun•eyed (see fig. 9.3A).

Eastern and many northwestern basins, especially those draining the Tsaratanana Massif, receive more rainfall and are more diverse geographically than the drier western and sourhern basins. Rivers in eastern and northwestern Mada­gascar are also Jess subject to large seasonal fluctuation in flow rate (Aidegheri 1972; Donque 1972). Most western basins experience periods of very reduced flow or complete desiccation during the dry season extending from April un­til November (Donque 1972), which could easily wipe out any existing populations of freshwater fishes inhabiting these areas. This pattern of seasonal desiccation likely ac­counts for the very depauperate assemblages of freshwater fishes inhabiting western basins, which in general are dom­inated by marine forms.

ln addition to these three primary regions of ichthyofau­nal diversity, a number of localized areas with unique and interesting fish assemblages are found throughout Mada­gascar. These indude the tshrgy formations of the nort hern and western regions of the island and the numerous lime­stone caves of the extreme southwest that are home to a small radiation of blind cave eleotrids (TyphiC!otris spp.). The central highlands and eastern coastal Madagascar also contain both lowland and highland Pandanus swamps, where a number of rare and highly stenotopic fish species occur, including members of Pantanodon and Bedotia. The larger rivers in southwestern Madagascar, near the PN de lsalo, are (or were) home to extremely rare and localized freshwater fish assemblages, including members of the gen­era Ptychochromoides, Ptychochromis (presumed extinct in this region), and Ancharius, whose closest relatives are restricted to eastern and southeastern drainages. The com­position and relationships of the ichthyofauna of the lsalo region are inreresting and suggestive of a recent prior con­nection with southeastern drainages. The largest satellite is­lands, Nosy Be and Ile Sainte Marie, are of recent origin and share most elements in common with the main island. The small crater lakes on Nosy Be are home to at !east one endemie Ptychochromis species.

Riseng (1997) compiled baseline data for most of the major drainage basins and compared disturbed and pris­tine sites for a number of water-quality parameters. On av­erage, western ri vers were fou nd to be warmer than eastern rivers, lower in conductivity, slightly higher in pH {being nearly neutra! versus slightly acidic for eastern rivers), and much higher in dissolved carbonates (i.e., alkalinity). Oxy­gen content was found to be similar for waters in both east­ern and western drainages. Oligotrophic flood plain lakes of western Madagascar were found to be warmer than eastern lakes, with higher conductivity, pH (7.3 versus 5.6), and

dissolved carbonates. Again, dissolved oxygen content was found to be similar regardless of hydrologie region.

Overview of the Freshwater Fish Fau na

Madagascar's ichthyofauna is numerically dominated by members of the Cichlidae, Bedotiidae, Gobiidae, Eleotri­dae, Anchariidae, Mugilidae, Anguillidae, and Aplochei­lidae {table 9.1). Small endemie radiations of bedotiids (endemie family; two genera), cichlids (five genera, ali en­demie), aplocheilids (one genus, endemie to Madagascar and granitic Seychelles), and anchariids (endemie family; one genus) characterize the insular rivers, streams, and lakes. However, the majority of families with members pres­ent on Madagascar are primarily marine and are frequent! y colonizers of oceanic islands. These include nwmbers of the Gobiidae, Eleotridae, Mugilidae, Ariidae, Syngnathi­dae, Anguillidae, Ambassidae, and Kuhliidae. lnterestingly, other than native eels of the genus Anguilla, the island Jacks large predatory species, but as discussed later in this ch<tp­ter, the Asian snakehead (Chamza cf. striata) was imro­duced in the 1960s and is currently devastating native fish populations throughout the island.

Madagascar's ichthyofauna is noteworthy a Iso for a Jack of families generally considered to represent "primary" freshwater fishes (Myers 1938), and representatives of only three so-called secondary freshwater families are present, the Aplocheilidae, Cichlidae, and Poeciliidae (Stiassny and Raminosoa 1994). The remaining familics with members present in Madagascar have generally been considered to represent either marine or "peripheral" families (but see later in this chapter). The term peripheral has traditionally been used to refer to primarily marine families with mem­bers that are permanent residents of freshwater habitats or chat require freshwater habitats at sorne point in their !ife cycle. Most surprising perhaps is the absence of a diverse ostariophysan fauna (catfishes, characins, and gonorhychi­formes) in Madagascar, which comprises the vast major­ity of so-called primary freshwater fishes worldwide and which is weil represented on other Gondwanan landmasses (i.e., South America, Africa, and India). However, we con­sider these physiological distributional generalizations to be restrictive and arbitrary and believe that in such cases it is not only more informative but a Iso necessary to adopt a phylogenetic approach. As stressed by Lundberg (1993), it is important to recognize the phylogenetic leve! at which subgroups within a clade show strictly freshwater distri­butions, and probably both Bedotiidae and Ancharii­dae should also be included as "secondary" freshwater families. Clearly the traditional "primary" and "second-

ary" distinctions of Myers (1938) are holdovers from a dis­persalist perspective of fish distributions (i.e., of explaining freshwater fish distributions without recourse to continen­tal drift scenarios), and as such they ignore much recent phylogenetic evidence chat brings into question and contra­diets the restrictions implied by these terms.

Madagascar is home to a surprisingly speciose gobioid fauna (table 9.1). Gobies and eleotrids are common throughout Madagascar and are frequemly the only fishes encountered in the headwaters of many of the steep and cascading rivers draining the eastern escarpment. This is particularly true of members of the genera Awaous and Sicyoptcms, ofren referred ro as "rock climbing gobies." These and related genera are commonly found above wa­terfalls of 10-20 rn and may even penetrare beyond sheer drops of 130 rn (Fitzsimons and Nishimoto 1990). Trog­loditié forms are also present on the island; a blind cave goby of the genus Glossogobius is found within the karst formations of Ankarana in northern Madagascar, and a small endemie radiation of blind eleotrids of the genus Ty­phleotris is restricted to limestone caves in the southwest (Arnoult 1959; Banister 1994; see Sparks, "Typhleotris," this volume).

As alreadr noted, Madagascar is home to two endemie freshwatcr families, the Bedotiidae, or Malagasy rainbow­fishes, with two genera (Bcdotia and Rheocles; see Loiselle and Stiassny, "Bcdotiidae: Bedotia," and "Rheocles," this volume), and a poorly known catfish family, Anchariidae, composed of a single genus (Ancharùts; see Ng and Sparks, "Ancharius," this volume). The phylogenetic relationships of bath of these groups are controversial. For example, Tay­lor ( 1986) places Attcl1arius wirhin the Ariidae, whereas de Pinna ( 1993) positions ir as their sister group. ln contrasr, Mo ( 1991) proposed that Ancharizts is most close! y related to the African freshwatcr family Mochockidae. Similarly phylogcnetic placement of the Bedotiidae is problematic and currently unresolved (see, e.g., Rosen and Parenti 1981; P;mnti 1984; · Stiassny 1990; Dyer and Chernoff 1996). There seems little current justification for readjust­ing the taxonomie rank of either of these two clearly mono­phyletic tax;l, and we retain bath Bedotiidae and Anchari­idae as valid familial designations. Inrerestingly, until recently bath of these endemie families were considered to be restricted to eastern drainages within Madagascar; nev­ertheless, surveys conducted within the past few years have discovered species belonging to bath families in western basins (table 9.1) (Stiassny and Rodriguez 2001; Ng and Sparks submitted).

Finally, Madagascar is home to severa! exrremel~· rare endemie and stenoropic freshwater species, including the atherinid genus Terdmulus (see Sparks, "Teramttltts," this

J. S. Sparks and M. l. J. Stiassny 859

volume), rediscovered only cecently from a single stream in northwestern Madagascar. Similacly, the enigmatic (poeci­liid?) genus Patttanodon (Arnoult 1963) is currently re­stricted in Madagascar to a single small Pandanus swamp (approximately 10 rn x 50 rn) along the sourheast coast (see Sparks, "Pantanodon," this volume). The presumed sister taxon to the Malagasy Pantanodon (two species, one presumed extinct) is found in eastern Africa (P. podoxys), although this taxon is morphologically quite distinct from the Malagasy forms (Rosen 1965).

Origins. Relationships, and Biogeography

For students of Gondwanan biogeography, the origin(s) and composition of Madagascar's extant freshwater fish fauna remain a mystery. Missing (in both the contemporary and the fossil record) are severa! major groups found in, but not necessarily restricted to, Africa. These include cypri­nids, characins, polypterids, mormyrids, and osteoglosso­morphs (Kiener and Richard-Vindard 1972; Stiassny and Raminosoa 1994). Madagascar Jacks representatives of families present nor only in Africa but also in lndia (and of­ten with ranges extending into Southeast Asia). These in­elude anabantids, bagrids, channids, clariids, cyprinids, mastacembelids, notopterids, and schilbeids. Further, many families present in South America, Africa, and Jndia­Southeast Asia are also conspicuously absent from Mada­gascar. Examples include cenrropomids, nandids, and syn­branchids (Berra 1981; Nelson 1994; see Stiassny and Raminosoa 1994, table 2, for a comprehensive list of Cami­lies present on various Gondwanan landmasses).

Interesting also is that a number of the taxa present on Madagascar represent the sister group co major assem­blages or radiations of related forms found elsewhere. In other words, many Malagasy taxa are cladistically ple­siomorphic (lacking derived features or characteristics thar are shared by other closely related species) with respect to their counterparts (i.e., closest non-Malagasy relatives) on other Gondwanan landmasses (e.g., Harrison and Howes 1991; Stiassny and de Pinna 1994; Dyer and Chernoff 1996). This phylogenetic pattern is perhaps not surprising considering the long-rerm isolation of Madagascar from other continental landmasses. But whatever the explana­tion, the result is a unique ichthyofauna characterized by many groups wirh members that retain a number of ple­siomorphic features but thar are highly derived in other re­spects when compared with their closest non-Malagasy rel­atives. This concentration of phylogenetically primitive taxa in Malagasy freshwaters is a major resource for evolu­tionar)' studies and a compelling additional argument for

860 Fishes Introduction

the importance of incorporaring rhese taxa inco regional conservation programs tSriassny 1992; Stiassny and Rami­nosoa 1994).

Before discussing the origins and affinities of Madagas­car's extanr ichrhyofauna, it is helpful to summarize paleo­geographie data bearing on the Mesozok fragmentation of Gondwanan landmasses (also see Krause, this volume). Re­cent data suggest thar Madagascar and lndia, or the lndo­Madagascar block, separared from Africa about 165 .Ma and thar Madagascar attained irs current position with re­spect ro Africa about 124 Ma (Storey 1995; Srorey et al. 1995). Although motion between the Indian subconrinent and Madagascar began as carly as about 135 .Ma, at about the same rime thar India began ro rift from Anrarctica, Madagascar and lndia remained in close proximity unril the Lare Cretaceous, about 88 Ma (Rabinowitz et al. 1983; Storey et al. 1995; Hay et al. 1999). As the Indian landmass continued to migrate rapidly northward in the Lare Creta­ceous, rifting between the granitic Seychelles and India oc­curred about 65-69 Ma (Piummer and Belle 1995; Srorcy 1995). Western Gondwanan rifting, between South Amer· ica and Africa, beg:m about 130 Ma, and the rwo llnd· masses were subaerially isolated by the Mid-Cretaceous (ca. 120-100 Ma; Srorey 1995; Hay et al. 1999).

lnterestingly, recent studies have also hypothcsized thar the lndo-Madagascar landmass and eastern Antarctica were in contact unril about 120 Ma (Storey 1995; Krause et al. 1997a) and possibly even weil into the Lare Crcta· ccous (ca. 80 Ma; Hay et al. 1999). Thus, ir is hypothe­sized thar at the end of the Cretaceous, under the revised reconstruction of Hay et al. (1999), subaerial (dry land) connections remained between ali the Gondwanan land­masses Jess Africa (Sampson et al. 1998; Hay et al. 1999). Potentially at least, freshwater corridors remained be­tween Madagascar-lndia-granitic Seychelles and possibly ail Gondwanan landmasses, less Africa, until very late in the Cretaceous.

Whether the absence of many widespread Gondwanan fishes from Madagascar's freshwaters is attributable to ma· jor extinctions on the island (for which there is currently no evidence) orto the fact that these groups were never pres· em will continue to be the subject of both paleontological and historical biogeographie studies. Representath·es of Madagascar's extant freshwater fish groups are conspicu­ously absent from Cretaceous deposits on the island (Gott· fried and Krause 1994, 1998; Krause et al. 1997b; see Krause, this volume), and prior ro the latc Pleistocene the island's Cenozoic fossil record is dominated by marine de­posits (Krause et al. 1997b). Furthcr, only a few families wirh exr:mt endemie species on Madagascar-for example, Ariidae-have a fossil record that currently extends back to the Cretaceous (Patterson 1993a,b; Gottfried and Krause

1998). This Jack of fossil evidence bas led paleontologists to conclude thar extant and recently extinct vertebrate taxa did not colonize the island until the Cenozoic (Krause et al. I997a; Gottfried and Krause 1998; Gottfried et al. 1998), weil after Madagascar was isolated by the Mesozoic breakup of Gondwana (Srorey et al. 1995; Hay et al. 1999). Thus, paleontologists hypothesize thar the island's extant fishes are descended from post·Mesozoic (intercontinental marine) colonizers, and not from frcshwater taxa isolated on Madagascar by the fragmentation of Gondwana.

However, as Maisey (1993) points out, absence of evi­dence is not evidencè of absence. Dcspite a lack of fossil corroboration, our current undcrstanding of the phyloge­netic relationships of many freshwarer fish clades presents a compclling argument in support of vicariance ilS an expia· nation of their present distribution. Groups with broadly Gondwanan distributions and members currently present on Madagascar include the Cichlidac, Aplocheiliidae, pel· lonuline Clupeidae, and Bedotiidae. Transoceanic sister· group relationships congruent wirh prevailing hypotheses of Gondwanan fragmentation have bcen hyporhesized for the cichlid genera Etroplus (lndia/Sri Lanka) and Parctro· plus (M:adag:tscar) (Cichocki 1976; Stiassny 199 J; Stiassny et al. 2001; Sparks in press), the family Cichlidae in general (congruent with the reviscd paleogeographie rc..:onstruc­tion of Hay et al. {1999]; j. Sparks unpubl. data), the Atherinoid families Bcdotiidae (Madagascar) and Mela· notaeniidae (Australia/New Guinea) + Pseudomugilidae (Australi:t/New Guinea/eastern Jndonesia) + Telmatheri­nidae (Sulawesi/New Guinea) (Dyer and Chernoff 1996; Aarn and Jvantsoff 1997), and between the aplocheilid gen­era Pachypanchax (Madagascar and Seychelles) and Aplo­cheilus (lndia/Asiatic) (Costa 1998; J. Sparks unpubl. data). Further, a close phylogenetic relationship is proposed be· tween a number of freshwater (i.e., continentally restricted) pellonuline clupeid genera with Gondwanan distributions (Grande 1985; Stiassny 2002}. An ehiravin clade compris· ing the pellonuline genera Sauvage/la (Madagascar), Ehi· rava (southern Jndia/Sri Lanka), Da)•clla (southwestern In­dia), Clupeichthys (Southeast Asia), Corica (India and Sourheast Asia), Spratellomorpha (Madagascar and eastern Africa), and Gilchristella (southern Africa) has been hy­pothesized by Stiassny (2002). Although relationships within the eh ira vin clade remain to be resolved, monophyly of this widespread, essentially Gondwanan freshwater clade is not incongruent with a vicariance expia nation for its cur· rent distribution.

With additional phylogenetic studies of Madagascar's freshwater and nearshore marine fish groups, additional biogeographie patterns congruent with Gondwanan frag· mentation are likely to emerge. For example, a sister-group relationship between the M:tscarene and lndian-southern

Asian sicydiine (rock-climbing) gobies of the genus Sicy­opterus is hypothesized (Sparks and Nelson in prep.). Such

· .historical biogeographie patterns elucidated by phylogeny provide insight into evolutionary processes (i.e., were spe­ciation/diversification events coïncident with the appear­ance of a barrier [vicariance], or does the barrier predate speciation (dispersal]?), which canin turn be used to ana­Jyze and explain present distributions (Lundberg 1993).

Formulation and testing of historical hypotheses regard­ing the origins and diversification of Madagascar's fresh­water fishes require knowledge not only of their phyloge­nies but also of their spatial and temporal distributions. Congruent biogeographie patterns exhibited by a number of distantly related clades present a compelling argument for vicariance (Rosen 1978). The sister-group relationships discussed earlier are consistent with current prevailing hy­potheses regarding the sequence of Gondwanan fragmenta­tion, given thar the connection of Madagascar, the granitic Seychelles, and India was more recent than thar of Mada­gascar to other Gondwanan landmasses and given the po­tential connecrion of South America, Madagascar/India, and Australia via Antarctica, exclusive of Africa, thar may have persisted weil into the Lare Cretaceous (Hay et al. 1999). Despite the problems with this interpretation, it seems to us improbable thar these congruent distributional patterns could have resulted from numerous independent intercontinental marine dispersals. ln light of these repeat­ing patterns, there is no need to contrive dispersalist sce­narios as alternative explanations, given thar vicariance is the most parsimonious explanation of the observed distri­butions (Grande and Bernis 1999). Moreover, it is inadvis­able a priori to dismiss vicariance in intercontinental faunal comparisons, even in the absence of fossil data, unless ir can be shawn for the organisms in question thar their closest relatives are marine taxa (Lundberg 1993; Stiassny and Raminosoa 1994). Based on our current systematic under· standing, we do not find this to be the case for the Bedoti­idae, Cichlidae, Aplocheilidae, or the ehiravin clupeid gen­era discussed earlier.

Finally, we note thar paleontological studies in Mada­gascar concerning fish are few, and the fossil record for many of the families in question is surprisingly poor, not only in Madagascar but also worldwide (Patterson 1993a,b; Murray 2000). As Grande and Cavender (1991) stress, there is a global paucity of Early Cretaceous through Mid-Paleocene freshwater teleosr fossils, which is probably attributable to a scarcity of fossil-bearing freshwater rocks of Cretaceous age (Lundberg 1998). Given the nature of freshwater systems, the likelihood of preservation of an­cient freshwater faunas is significantly less than under ma­rine conditions. Only recently have fossil gars, large and rather conspicuous animais, been discovered in Cretaceous

-------------------------------------

J. S. Sparks and M. L. J. Stiassny 861

deposits on Madagascar (Gottfried and Krause 1998). This recent discovery supports our contention thar the current absence of fossil evidence corroborating the early presence of Madagascar's extant freshwater fishes does not rule out the possibility thar their fossils will someday be discovered there.

Conservation: Current and Future Threats

Bensread er al. (2000) consider three main factors to ac­count for the current dire state of the Malagasy ichchy­ofauna: the degradation of aquatic habitats thar follows de­forestation (fig. 9.20), overfishing, and competition from and predation by exotic species. To chis list we would add a "knowledge impediment," by which we mean a lack not only of comprehensive knowledge of the taxonomie com­position and status of the island's ichthyofauna but also of the most basic biology of the majority of species.

Des pire this knowledge impediment, what is ali too clear is thar sedimentation and increased rurbidity of river and lake basins have major effects on native fish populations, whereas exotics seemingly thrive in and dominate these highly degraded habitats. Severa! species of tilapiine cich­lids, introduced for aquaculture purposes decades ago (seè Reinthal and Stiassny 1991, table 4, for a complete list of introductions), compete for resources with native species, and large exotic predators such as the Asian snakehead (Channa cf. striata) and black bass (Micropterus salmoides) prey heavily on native fishes. In particular, the introduction of the Asian snake head, a voracious predaror thar is rapidly spreading throughour the island, appeaxs to be having a major impact on native fish populations (Benstead et al. 2000; ]. Sparks and M. Stiassny pers. observs.). Unfortu­narely, human-mediated disturbances will play an increas­ingly significant role in the attrition rate of native species, as Madagascar has one of the highesr population growth rates in the world ar 3.2% (Population Reference Bureau 1997-2001; Kremen et al. 1999). Green and Sussman (1990), us­ing Landsat images, esrimate thar annual forest loss in Madagascar is 1100 km2, whereas orher estimates range as high as 3000 km2 per year (Richard and O'Connor 1997). Problems associated with annual forest-cover Joss are dis­cussed elsewhere in this volume (see Dufils), and the out­look is bleak. Overfishing, primarily with the use of gill nets, is a major concern in sorne of the large floodplain lakes in the northwestern (including Lac Kinkony and Lac Andrapongy, as weil as the lakes in the region of Saro­drano) and eastern regions of the island (coasrallakes of the northern Pangalanes Canal).

Ali of Madagascar's large lakes are curremly infested wirh the Asian snakehead, which has already resulted in

862 Fishes Introduction

dedining fish catches and will likely lead to the collapse of native fisheries in the near future. Species that have only recently been discovered, including Paretroplus menarambo

. (Allgayer 1996) from Lac Sarodrano in the northwest, are now verging on extinction (or are extinct, as no additiona! specimen of this recently described taxon has been collecred si nee 1997), apparent! y as a direct result of heavy predation by the snakehead. A number of species appear already ro have succumbed to these pressures and are presumed ex· rinct (Harrison and Stiassny 1999). To these should be added an undescribed species of Ptycllochromoides from Lac ltasy in the central highlands, an undescribed Ptycbo· chromis species from the Onilahy River basin in the south­west, and Pantanodon madagascariensis from eastern coastal swamps (]. Sparks and M. Stiassny unpubl. data).lt has been suggested thar species inhabiting islands may be more susceptible to extinction because of a high degree of specialization and low b·els of competition wirh orher species (MacArthur and Wilson 1967; D'Antonio and Dud­ley 1995), and this appears to hold true for the Malagasy ichrhyofauna.

The vulnerability of the island's freshwarer ichrhyofauna as a whole is exacerbated by extreme stenotopy of numer­ous native species. Many endemie cichlids and bedotiids ex­hibit restricted geographie distributions and are known only from their type localities or at most a very localized a rea, frequently a single body of water or an isolated drain­age basin. Regional endemism is high (table 9 .1, fig. 9.3A), especially in the north western and eastern regions of the is­land. Sparks and Rein thal ( 1999) present a currem distri­bution map for members of Paretroplus, illustrating their extremely localized distriburions in the northwest, and Sti­assny and Rodriguez {200 1) depict similarly restricted dis­tributions for Rheocles species in the eastern drainages. In addition to Parctroplus and Rheocles, other highly steno­tapie species include Oxylapia po/li, Ptychochromoides katria, Pantmwdo11 nov. sp. "manombo," Teramulus water­loti, Glossigobius ankararrensis, and the species of T;•phleo­tris restricted to limestone caves in south western Madagas­car, to name but a few. As Raxworrhy and Nussbaum (1997) point out, interest in the biogeography of Madagas­car's flora and fau na has been high at a global scale, but rel­atively little attention has been directed at within-island biogeographie patterns for vertebrates. Although severa! re­gions with highly endemie fish communities can be iden­tified (e.g., northwestern lakes and basins, the basins of the Mangoro, Ankofia, and Mangarahara, and Lac Kinkony), including disjunct geographie regions wirh interesting sim­ilarities in ichthyofaunal composition suggestive of recent hydrologie connection {e.g., southwestern Madagascar !Isalo region}, southeastern highlands [Vevembe-Vondrozo

region]), imraisland biogeographie patterns of fish distribu­tions ha\·e rer to be fully investigared.

As is the case in so many of the world's top conservation "hotspots," freshwater systems are frequently overlooked, and this has had tragic consequences not only for aquatic communities but also for the terrestrial systems thar depend on them. ln Madagascar, river systems are commonly ex­duded from protection, even if surrounded by prorected land, as these riparian areas are the most desirable for slash-and-burn agriculture and paddy rice production. This is not to say tbat conservation efforts are always futile. An ichth)·ofaunal survey of the Masoala Peninsula conducted in recent years was instrumental in ensuring the inclusion of river basins inro the design of the PN de Masoala (Kremen et al. 1999). Although in most cases protection of Mada­gascar's aquatic systems has not been a top priority, we hope thar by presenting the freshwater fish fauna in a new light, by srressing its importance for evolurionary studies, its high degree of vulnerability, and the current dire state of the fauna as a whole, the conservation community will be­gin the process of fully inregrating aquarie habitats inro fu­ture conservation action.

Conclusions

Alrhough our original intention was to present an in-depth discussion of conservation recommendations directed spe­cifically at preserving aquatic communities in Madagascar, we now believe rhat most of what we could suggest would faU far short of succeeding and wou Id most Jikely be futile. We have both conducted research in a number of tropical regions, but neither of us has witnessed anyrhing surpass­ing the degree and extent of environmental degradation in Madagascar. The freshwater fish fauna of Madagascar is al­ready so heavily affected that it is likely too late to save ali but small remnants. Madagascar willlikely be one of many large islands to have its native floras and faunas heavily af­fected by human influence.

Our position may be interpreted as overly pessimistic, but that is partly our intention. We do not believe it helpful to propose a series of emergency measures to "save" what remains, when in fact we believe that most of these mea­sures would prove tao little and much too lare. At least for the rime being, in certain isolated parts of the island, in­cluding the Masoala Peninsula and remote regions in the east and northwest, forested basins remain, and every effort must be made to save them. The large offshore island of Nosy Be is currently free of exotic predators (P. V_ Loiselle unpubl. data), retains a native ichthyofauna, and must be considered a top conservation priority. Unfortunately,

snakehead fry have been discovered on Madagascar's other large offshore island, Ile Sainte Marie (]. P. Benstead un­pub!. data), and likely foreshadow the demise of this is­\and's native fish fauna.

The situation throughout much of western, northwest­ern, central, and eastern Madagascar is far direr. A number of small forested regions have been afforded protection, but these reserves and parks do little in the sense of offering pro­tection to entire river basins, given thar aquaric systems are so vulnerable to upstream influences. Many of Madagas­car's reserves are sim ply too small to maintain viable popu­lations of native fish species, especially species thar must migrate either short or long distances during reproduction or thar require large and diverse habitats.

Extremely localized distributions and concentrated re­gional diversity point to a particular vulnerability of the Malagasy ichthyofauna as a whole. Species are generally represented in smaller areas of their overa\1 range and may not be affected by initial restricted habitat destruction (or in the case of Madagascar's freshwater fishes, dist ributions are generally very localized, and populations may escape initial habitat destruction). Although habitat loss may ini­tially cause relative! y few extinctions, eventually many will result as the last p;ucels are destroyed (Pimm and Raven 2000). Nowhere is this more truc than in Madagascar, which is poised for a "breaking wave" of species extinction in the coming decade. To date, endemie and native fish spe­cies have becn completely replaced by exotics across most of the central highlands and throughout much of the west (Reinthal and Stiassny 1991; J. Sparks and M. Stiassny un­pub!. data) . Somc 23 cxotic specics have been deliberarely introduced into the island's freshwatcr systems dating from the mid-1800s, not to mention a number of accidentai es­capees from aquaculture in recent deçades {Reinthal and Stiassny 1991; Bensread et al. 2000). Unless drastic mea­sures are undertaken to protect this fragile fauna, as has been the case for many of Madagascar's terrestrial organ­isms, much of the island's native freshwater fishes will be )ost forever. Given the islandwide spread of exotics, such measures will have to include captive breeding programs {see Loise!le, "Captive Breeding for the Freshwater Fishes of Madagascar," this volume), the poisoning of lakes and rivers to eliminate these introduced species, and restocking with native species, not to mention large·scale restoration of these degraded habitats. However, as Benstead et al. (2000) point out, no restoration projects are currently in progress or p lanned. Although it may already be too lare to save ali but remnants of Madagascar's unique freshwarer ichthyofauna, it is our hope thar this tragic story will serve as a warning and underscore the importance of carly pro-

J. S. Sparks and M. L. J. Stiassny 863

rection of vulnerable island freshwarer ecosystems else­where in the world.

Acknowledgments

We are extremely grateful to numerous colleagues rhrough­out the world for their help with this project. Ali have been generous with their time and insights into Malagasy fishes and often also in providing us with data and specimens for this study. ln parricular, we thank Paul Loiselle, who has been a resource of inestimable value throughom the study. His input on an earlier dra ft of this chapter is much appre­ciated and much improved the final product. Thanks a iso to Chris Raxworrhy for commenting on an earlier dra ft of this manuscript. Our thanks also to Robin Abel! and Michele Thieme, whose efforts associated wirh the WWF freshwater assessment of Africa have been a source of inspiration. It was at their urging thar we firsr began the process of assim­ilating data on Malagasy fishes, and we are appreciative of their ongoing moral support. Thanks to Karen Riseng, Franco Andreone,Jean Claude Nourissat, Patrick de Rham, Alex Saunders, Paul Loiselle, and John Barnes for providing us wirh data and specimens from recent field work and to

Patrice Pruvost and Guy Duhamel (Paris), Darrel Siebert and Oliver Crimmen (London), Martien van Oijen (Lei­den), Barb Brown (New York), Susan Jewert (Washington, D.C.), and Claude Weber (Geneva) for sending materials on loan. Doug Nelson (Ann Arbor) was extremely helpful with the curation of numerous materials.

For assistance in Madagascar we are exrremely grateful ro Noro Raminosoa, Peter Reinthal, and Patricia Wright. Collecring efforts were facil itated by Benjamin Andriama­haja and Ml CET (Institute for the Conservation of Tropical Environments, Madagascar) staff, and we are grateful for their support. Collection permits were obtained from the Direction des Eaux et Forêts and the Association Nationale pour la Gestion des Aires Protégées (ANGAP). Melanie L. J. Stiassny acknowledges the ongoing support of an Axel­cod Curatorship. John S. Sparks's work was funded by grants from the National Science Foundation (DEB-9300996), the United States Agency for International De­velopment (University Development Linkage Program, US­AID Cooperative Agreement, PCE-5063-A-00-3035-00) given to Peter Reimhal, and the Carl L. and Laura C. Hubbs Research Fellowship; support from the Rackham School of Graduate Studies of the University of Michigan; and a collection study grant awarded through the American Museum of Natural History.

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