experiences on importance of diet for shrimp …aquaculture 191 2000 169–176 . experiences on...

Ž .Aquaculture 191 2000 169–176www.elsevier.nlrlocateraqua-online

Experiences on importance of diet for shrimppostlarval quality

Patrick Lavens, Patrick Sorgeloos)

Laboratory of Aquaculture and Artemia Reference Center, Ghent UniÕersity, Rozier 44,9000 Ghent, Belgium

Received 1 March 2000; accepted 9 May 2000

Abstract

This paper gives an overview of own experiences with respect to the impact of dietaryconditions on the quality of postlarval penaeid shrimp. Direct nutrient-specific effects are

Ž . Ž .documented for highly unsaturated fatty acid HUFA , phosphatidyl choline PC and ascorbicŽ .acid AA . Specific immunostimulants may also contribute to an improved stress resistance of the

shrimp fry. Last, but not least, some emphasis is placed on the role of the microflora during thehatchery rearing, the possible reduction of bacteria in the live food administered, and the use ofprobionts through the diet. q 2000 Elsevier Science B.V. All rights reserved.

Keywords: Shrimp; Postlarva; Artemia; Food; HUFA; Immunstimulants; Microflora

1. Introduction

Shrimp production has experienced, ever since the early 1980s, an exponentialgrowth. However, during the last years, considerable concern has been raised withrespect to the sustainability of shrimp farming worldwide. One of the major reasonsbeing the temporal production catastrophies in many countries, e.g. Taiwan, P.R. China,Ecuador, Thailand, due to disease outbreaks. Solutions to overcome this inconsistency inproduction were searched for mainly in the fields of de-intensification of the grow-outtechnology, improvement of shrimp immunity and disease control. However, the quality

Ž .of the postlarvae PL to be stocked in the nursery and grow-out ponds may also

) Corresponding author. Tel.: q32-9-2643754; fax: q32-9-2644193.Ž .E-mail address: [email protected] P. Sorgeloos .

0044-8486r00r$ - see front matter q2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0044-8486 00 00426-9

( )P. LaÕens, P. SorgeloosrAquaculture 191 2000 169–176170

contribute to a more sustainable production. For example, in Latin America, wild PL ofLitopenaeus Õannamei are still preferred over hatchery-produced PL as seed material, asthey guarantee higher production outputs in the ponds. The lower quality of hatchery PLis blamed to the lack of natural selection, use of unnatural food items and a lowadaptability to the natural environment. Recent research has demonstrated that optimisa-tion of the hatchery production through better dietary regimes, use of immunostimulantsand a better control of the microflora, results in a predictable availability of cost-effec-tive and high quality fry, as will be highlighted in this short overview from ownexperience at the Artemia Reference Center.

2. Direct nutritional effects on postlarval quality

The nutritional value of Artemia spp. nauplii, still the major food organism used forculturing shrimp PL, varies highly among geographical sources, especially in the content

Ž . Ž .of the essential fatty acid eicosapentaenoic acid 20:5ny3 EPA Leger et al., 1986 .´However, the biochemical composition of Artemia can easily be manipulated throughapplication of the bioencapsulation technique using emulsified marine oils containing

Ž . Ž .high levels of EPA and docosahexaenoic acid 22:6ny3 DHA Leger et al., 1987 .´It has been documented by several authors that feeding highly unsaturated fatty acid

Ž .HUFA -enriched Artemia to PL of Penaeus monodon resulted in improved PL quality,Žexpressed as their ability to survive an exposure to a salinity shock Table 1; Tackaert et

. Ž .al., 1992; Rees et al., 1994; Kontara et al., 1995 . Rees et al. 1994 furthermoreŽdocumented that very high dietary levels of 31 mgrg DW HUFA DHArEPA ratio of

.0.5 did not improve postlarval stress-resistance, suggesting that an excessive supply ofHUFA may not be beneficial to the shrimp. Other lipid components such as the lecithin

Ž .phosphatidyl choline PC may result in similar effects, as was demonstrated by CamaraŽ . Ž . Ž .et al. 1997 and Kontara et al. 1997, 1998 , respectively, and Coutteau et al. 2000 for

P. japonicus and L. Õannamei PL fed an artificial diet only varying in the level ofsoybean PC. For both species, 1.5% inclusion of PC in the diet resulted in a significantincrease in stress resistance, expressed as mortality after exposure for increased time

Ž .intervals to de-ionised water Fig. 1 . Microscopic studies of the hepatopancreas furtherrevealed clear differences at the cellular organisation level between both PL groupsŽ .Kontara, 1997 .

Table 1Mortality rates of P. monodon PL, fed Artemia nauplii enriched with different levels of HUFA, afterchallenge to an osmotic stress test

Ž .Postlarval stage Salinity Mortality 24 h after challenge % Referencestress condition Low- Medium- High-

HUFA diet HUFA diet HUFA dieta bŽ . Ž .PL 10 1 h at 7 grl 82 6 – 15 5 Tackaert et al., 1992a b cŽ . Ž . Ž .PL 10 2 h at 10 grl 75 2 35 15 10 2 Rees et al., 1994a bŽ . Ž .PL 15 1 h at 10 grl 73 7 – 13 4 Kontara et al., 1995

Ž .Values within the same row with the same superscript are not significantly different P )0.05 ; ns3.

( )P. LaÕens, P. SorgeloosrAquaculture 191 2000 169–176 171

Ž . Ž .Fig. 1. Effect of soybean lecithin PC supplementation on stress sensitivity of postlarval shrimp. a L.Ž . Ž . ŽÕannamei data from Coutteau et al., 2000 ; b P. japonicus data from Camara et al., 1997; Kontara et al.,.1997a, 1998 .

Vitamins may also play an important role in improving the quality of hatchery-pro-duced fry. Culture tests with vitamin C boosted microbound diets for PL of P. monodonŽ . Ž .Merchie et al., 1998; Lavens et al., unpublished data and L. Õannamei Kontara, 1997

Ž .confirmed the hypothesis that dietary ascorbic acid AA improved the overall physio-Ž . Ž .logical condition in PL Table 2 . In similar experiments, however, Lavens et al. 1999

could not reveal any differences in stress resistance for PL of L. Õannamei. On the otherŽ .hand, Kontara 1997 could observe an optimal resistance to a Vibrio harÕeyi infection

Ž .when L. Õannamei PL were fed a megadosis of vitamin C 2000 mg AA equivalentrkg


Table 2Mortality rates of shrimp PL fed microbound diets with different levels of vitamin C, after challenge to anosmotic stress test

Ž .SpeciesrPL stage Salinity stress Mortality 24 h after challenge % Referencecondition 0 mgrkg 100 mgrkg 2000 mgrkg

1 1 1vitamin C vitamin C vitamin Cin diet in diet in diet

a b cŽ . Ž . Ž .L. Õannamei PL 40 1 h at 0 grl 67 10 37 6 10 8 Kontara et al., 1997a a aŽ . Ž . Ž .L. Õannamei PL 36 1 h at 8 grl 95 1 95 1 94 1 Lavens et al., 1999

a bŽ . Ž .P. monodon PL 40 2 h at 0 grl – 83 2 56 7 Merchie et al., 1998a a bŽ . Ž . Ž .P. monodon PL 25 1 h at 0 grl 91 3 91 4 94 4 Lavens et al., unpublished data

Ž .Values within the same row with the same superscript are not significantly different P )0.05 ; ns3.1Expressed as AA equivalents.

Ž .Fig. 2 . An increase in the astaxanthin levels from 230 to 810 mgrkg in the diet of P.Žmonodon also resulted in a significant drop of the stress index cumulative mortality

.index during an osmotic shock; Merchie et al., 1998 from 56 to 33.

3. Effect of immunostimulants on postlarval quality

The use of immunostimulants has gained a lot of interest as a valuable alternative tothe use of antibiotics and vaccines in the fight against infectious diseases in shrimp

Ž . Žfarming Subasinghe, 1997 . A number of commercial products yeast preparations,

Ž .Fig. 2. Cumulative mortality of L. Õannamei PL, fed microbound diets containing respectively 0 AA 0 , 100Ž . Ž .AA 100 and 2000 AA 2000 mgrkg equivalents of AA, as a result of an infection with V. harÕeyi from 2

Ž .weeks of rearing onwards modified from Kontara et al., 1997b .


.b-glucans, polysaccharides are nowadays available, all claiming to have positive effectsŽ .on disease resistance Devresse et al., 1997 . We only report here on recent experiments

run with specific immunostimulants.Ž .A commercial booster Dry Immune Selco; DIS, INVE Aquaculture, Belgium ,

containing a mix of immunostimulants, vitamins C and E, was developed for bioencap-Ž .sulation in Artemia. P. monodon PL11 were fed non-enriched control or DIS-enriched

Artemia for 5 days. Already, 24 h after the start of the experiment, the DIS groupshowed a significantly lower mortality than the control treatment when the animals were

Ž . Žsubmitted to a salinity stress test 1 h at 0 ppt , i.e. 20% vs. 90% Dehasque et al.,. Ž1996 . Similar results were reported by the same authors for P. indicus PL16 stages not

.published .Ž .A microparticulate diet Stresspak, INVE Aquaculture , containing high levels of

selected micronutrients in combination with immunostimulants, was developed as apartial replacement of live food with the aim to fortify the shrimp PL during transporta-tion and just after stocking in the ponds. These handling conditions are considered asvery stressful and may normally result in a substantial mortality of the PL. A 50%supplementation of this diet for 14 days from PL1 stage onwards resulted in a 30%

Žhigher survival after subsequent 12 h transportation to the nursery Dehasque et al.,.1996 .

4. Better control of microflora during hatchery rearing

The live food used in larviculture operations is an important source of microbialŽ .contamination Verdonck et al., 1994 : for example Artemia nauplii are heavily

7 Ž .contaminated with bacteria, i.e. more than 10 colony forming units CFU rg, mostlyVibrio spp. These bacteria may be potentially pathogenic, or may stress the PL up to thepoint that they become more susceptible to viral infections. Several reports have shownthat disinfection and even decapsulation of the cysts prior to hatching incubation doesnot prevent bacteria to develop during the final hours before harvesting of the nauplii.Furthermore, thorough washing of the hatched nauplii does not have a significant effecteither on microbial contamination levels. Application of the recently commercialised DC

w Ž .Artemia cysts INVE Aquaculture results in a drastic reduction of the bacterialnumbers in the hatching water all the way through the hatching incubation of the cysts,

7 Ži.e. at harvest of the nauplii bacterial levels reach 10 CFUrml total counts, use ofŽ .. 3marine agar MA in control tanks vs. 10 CFUrml in the DC-treatment, Vibrio levels

Ž Ž .. 6 2specific counts, thiosulphate–citrate–bile–sucrose agar TCBS are 10 vs. 10CFUrml; a comparable pattern is observed with regard to bacterial load of the nauplii

w Žitself: nauplii hatched out of DC cysts contain 10,000 times less bacteria both on MA. Ž .and TCBS than the control Merchie et al., 1997 . Microscopic examination of the cysts

24 h after incubation reveals the presence of filamentous bacteria, protozoa and otherŽ .epizoics on the cyst surface of the control group only Fig. 3 . Similarly, after 24-h

w w Ž .enrichment of the nauplii with Selco vs. DC Selco INVE Aquaculture , bacterialcontamination levels are 108, respectively 105 CFUrml for total counts and 108 and 104

CFUrml for Vibrio.


Ž .Fig. 3. Microscopic views of the cyst surface 24 h after incubation. a Control: presence of filamentousŽ . Ž .bacteria, protozoa, etc.; b DC Artemia cysts: clean cyst surface from Merchie et al., 1997 .

The control over the microflora in the shrimp hatchery can be further optimisedthrough the application of more enforced hygiene, the use of modular units strictlyseparating the different hatchery sections, the adoption of regular shutdowns and


sterilisation periods in-between production cycles, the use of probiotics and a minimalŽuse of antibiotics. During the last years, several hatchery operators especially in Latin

.America are inoculating larviculture tanks with selected Vibrio species that haveŽ .so-called probiotic effects Griffith, 1995 . This empirical development certainly has

great potential but a more thorough scientific approach is required to develop well-docu-mented and effective methods for microbial management in larviculture systemsŽ .Rombaut et al., 1999; Verschuere et al., submitted . Finally, the use of antibioticsshould be disapproved, not only for prophylatic but even for therapeutical treatment. Inthe latter case, it should be restricted to oral treatment only, for example through the

Žapplication of the bioencapsulation technique with Artemia Verpraet et al., 1992;.Robles et al., 1998 .

Acknowledgements

Our research activities dealing with shrimp larviculture have been supported bygrants and contracts from the Belgian National Science Foundation, the Belgian Ministryof Science Policy, the Belgian Administration for Development Cooperation, theEuropean Commission, and INVE Aquaculture, Belgium.

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