Philippe Dhert

Use of the brine shrimp, Artemia spp., in marine fish larviculture.

Since no artificial feed formulation is yet available to completely substitute for Artemia, feeding live prey to young fish larvae still remains essential in commercial hatchery operations. The nutritional quality of commercially available Artemia strains being relatively poor in Ž. Ž

Advancement of rotifer culture and manipulation techniques in Europe

Abstract Since no artificial feed formulation for first feeding of marine larval fish has been developed yet, live prey feeding remains essential in commercial marine hatchery operations. Because cultured rotifers are relatively poor in eicosapentaenoic acid (EPA: 20:5n-3) and docosahexaenoic acid (DHA: 22:6n-3), it is essential and therefore common practice to enrich these live prey with emulsions of marine oils. The short-term exposure to oil emulsions results in lipid-encapsulated rotifers with high EPA and DHA levels. However, these rotifers are prone to fast losses of their gut content and show a distortion in their protein/lipid balance. Rather than submerging rotifers in oil emulsions, it is often preferred to use formulated culture diets when medium to low enrichment values are needed in live prey. The use of these diets contributes not only to the filling of the gut of the rotifers with nutrients, it generally creates a more stable entire body composition which is important especially when rotifers are not consumed immediately by the larvae. New culture techniques for rotifers, such as closed recirculation systems, are offering new possibilities for continuous supplies of high quality rotifers at 10 times higher densities than in batch cultures. The production increase in these systems is explained by the better water quality obtained by the introduction of protein skimmers, ozone treatment, and biological filtration. Although disinfection of rotifers remains a bottleneck, it has been observed that rotifer populations cultured at high densities are not prone to higher bacterial infestation. Also, the problem of unexplained mortalities in batch cultures seems to be partly solved by the introduction of recirculation systems or by bacterial management (introduction of probionts), which allow more reliable rotifer production.

Effect of Dietary Essential Fatty Acids and Vitamins on Egg Quality in Turbot Broodstocks

Varying egg quality is one of the main factors interfering with the reliable performance of marine fish hatcheries. As larval performance during the first period largely depends on the availability of essential nutrients, the endogenous provision of these nutrients through the egg stages, and possibly parental diet, might be an important tool in improving hatchery output. Therefore, several feeding experiments were conducted on turbot (Scophthalmus maximus) broodstock reared under production conditions at two commercial facilities in France: France Turbot (FT) and Sepia Conseil (SC). Diets varied mainly in essential fatty acids (ω-3 HUFA), Vitamins C and E, and were fed for 2–3 months prior to the reproductive season. Egg quality parameters, i.e. fertilization and hatching rate, egg and oil droplet diameter, and biochemical composition, were monitored for each female during its total reproductive phase.Egg size during the reproductive cycle showed a low variability among females receiving the same treatment, but became significantly smaller as the season progressed. The same occurred for the oil globule in the non-vitamin supplemented groups, whereas it significantly increased in the vitamin-supplemented groups. However, these observations could not be correlated with any of the hatching or fertilization characteristics. The egg dimensions also varied as a function of the diet supplied, i.e. high HUFA levels in the broodstock diet resulted in a significant increase of egg diameter, oil globule diameter as well as fertilization rate. Interestingly, the control groups, with the lowest fertilization rate, had the highest hatching percentage, significantly higher than the HUFA/non-vitamin enriched groups.Using non-selected sources of trash fish as a food source at SC resulted in low levels of ascorbic acid (AA) in the eggs compared to the administration of an optimal quality batch of mackerel at FT. Enrichment of the trash fish with ascorbate-2–polyphosphate (ApP) resulted in a tripling of the AA content. Extra enrichment of the FT control diet did not further increase the levels in the eggs, suggesting that a saturation level was obtained. The major fatty acids in turbot eggs as well as freshly hatched larva are 16:0, 18:1ω-9, 20:5ω-3 and 22:6ω-3, but no obvious changes in their pattern could be detected for the different broodstock treatments. However, the level of 20:4ω-6 was significantly higher in the control group of FT, and showed a high correlation with the hatching percentage of the eggs obtained from the various broodstock treatments.

Improved larval survival at metamorphosis of Asian seabass (Lates calcarifer) using ω3-HUFA-enriched live food

Abstract Asian seabass (Lates calcarifer) larvae were fed Brachionus cultured on Chlorella and, as soon as ingestin was possible, different types of Artemia, i.e., nauplii of the San Francisco Bay (SFB) strain, Great Salt Lake (GSL) strain or GSL nauplii that had been bioencapsulated with an emulsion containing high levels of the ω3-HUFAs (highly unsaturated fatty acids) 20:5 and 22:6. San Francisco Bay Artemia with a good natural fatty acid profile and small body size could be offered earlier than the larger but HUFA-poor Great Salt Lake strain. The poor nutritional quality of the latter, however, could be corrected by enriching the nauplii with an ω3-HUFA emulsion for 24 h, after which time high levels of the ω3-HUFAs 20:5 and 22:6 were obtained. When the Artemia diet offered before metamorphosis included natural or supplemented essential fatty acids, no significant differences in dry weight, length or survival of the fish were noticed, as compared to fish fed the naturally deficient GSL Artemia. Onset of metamorphosis and physiological condition after metamorphosis, however, were influenced by the HUFA content of the ingested prey. Seabass larvae fed SFB or enriched GSL Artemia started metamorphosis on day 19, while those in the non-enriched series never achieved metamorphosis and died of a nutritional deficiency syndrome by day 27. An indication of the physiological condition of the larvae and the early detection of the syndrome was possible by subjecting 21- and 25-day-old larvae to a stress test: abrupt exposure of the larvae to 65-ppt saline water resulted in abundant and early mortality in HUFA-deficient fish larvae. Fry receiving ω3-HUFA-fortified Artemia had a superior physiological condition which was reflected by significantly lower mortality figures in the stress test.

Recent developments in the application of live feeds in the freshwater ornamental fish culture

The industrial development of freshwater ornamental fish culture has been hampered by the lack of suitable live feeds for feeding the fish at the various production stages. This paper reports the recent developments in the applications of the freshwater rotifers (Brachionus calyciflorus), Artemia nauplii, decapsulated Artemia cysts and on-grown Artemia in the freshwater ornamental fish culture. Results demonstrate that the rotifers are an ideal starter feed for dwarf gourami (Colisa lalia), a typical freshwater ornamental fish species with larvae that are too small to ingest Artemia nauplii or Moina at its first feeding. Compared with the conventional yolk food, the use of rotifers as a starter feed significantly improves the growth and survival of the gourami larvae (Days 2–12), and the beneficial effects are extended to the subsequent Artemia-feeding phase (Days 13–32). The freshwater rotifers and Artemia nauplii are also useful in raising Discus larvae in the absence of their parents, which would eliminate the risk of larvae being eaten by the parent fish. Work on decapsulated Artemia cysts indicates that the cysts could be used as a substitute for Artemia nauplii or Moina in freshwater ornamental fish culture. The fry of all the five common ornamental fish species tested (guppy Poecilia reticulata, molly Poecilia sphenops, platy Xiphophorus maculatus, swordtail Xiphophorus helleri and neon tetra Hyphessobrycon herbertaxelrodi) could readily feed on the decapsulated cysts, and their performances in terms of stress resistance, growth and survival are comparable to or better than those fed on Artemia nauplii or Moina. A culture system for production of on-grown Artemia has also been developed specifically for the use in freshwater ornamental fish farms. The system, using diluted artificial seawater of 20xfor culture, has a mean production rate of 3 kg/m 3 of water in a 12-day cycle and a production capacity of 8 metric tons of on-grown Artemia a year. With the system, farmers could produce any specific size of on-grown Artemia of up

Search for beneficial bacterial strains for turbot (Scophthalmus maximus L.) larviculture.

The aerobic bacterial flora in the gut of turbot larvae and their influence on larval survival was examined. Two turbot experiments were run with six replicates each time. Large variation, from 0% up to 44%, was observed in the survival percentage of turbot larvae. There was no correlation between the number of bacteria present in the gut of turbot larvae and the larval survival rate. During both experiments, all replicates followed nearly the same rate of bacterial development in the gut of turbot larvae going from circa 102 CFU larva−1 just before first feeding at day 3 post hatch to 105 CFU larva−1 at day 9 post hatch. In total, 127 bacterial isolates from 12 rearing tanks were sampled for further investigation. Based on their fatty acid profile obtained by FAME-analysis, and using principal component analysis, the isolates were subdivided in 12 major gaschromatographic-groups or clusters (GC-groups), 11 isolates remained unclustered. Four specific GC-groups (namely cluster A, B, I and J) were selected as potential beneficial bacteria for turbot larviculture as the majority of the isolates of these clusters derived from rearing tanks with a survival percentage higher than 35%. Representative isolates of these clusters were screened on their ability to enhance the survival rate as well as the poor reproducibility in larval survival in a small-scale turbot confrontation test. Also, a Vibrio mediterranei Q40 strain, isolated from sea bream larvae, was included in these small-scale confrontation tests. Only cluster A and the V. mediterranei Q40 strain had a distinct positive and reproducible effect on larval survival. In conclusion, cluster A and V. mediterranei Q40 seemed to play a role as first coloniser of the gut of turbot larvae and could prevent the colonisation of the gut by opportunistic bacteria.

Use of Brine Shrimp, Artemia spp., in Larval Crustacean Nutrition: A Review

Because of convenience in production and their suitable biochemical composition, brine shrimp Artemia spp. nauplii have been adopted as a standard diet in the commercial larviculture of several crustacean species. The nutritional value of Artemia, however, is not constant, but varies both geographically and temporally. During the past decade both the causes of Artemia nutritional variability and methods to improve poor-quality Artemia have been identified. Enriching Artemia spp. with emulsified lipophilic products is a technique that has allowed delivery of extra doses of essential nutrients, for example, highly unsaturated fatty acids (HUFA) and vitamins, to crustacean larvae. The enrichment technique has limitations, however, because the Artemia spp. currently available selectively catabolize some of the nutrients such as docosahexaenoic acid and phospholipids. Decapsulated Artemia cysts, juveniles, and adult brine shrimp are also used increasingly as suitable diets for different crustacean species.

High-density production of the rotifer Brachionus plicatilis in a recirculation system: consideration of water quality, zootechnical and nutritional aspects.

Rotifers were reared on the artificial diet culture Selco® in batch and recirculation conditions at different water exchange rates. The different rearing conditions resulted in considerable changes in water quality, which in their turn affected rotifer growth and food consumption. At a daily water exchange rate of 100%, no positive effect was obtained in rotifer growth compared to the batch rearing system, but the rotifer culture period could be prolonged by 1 week. By increasing the daily water exchange rate from 100 to 300% the maximum rotifer density could be significantly (P<0.05) increased from 1800 to 2500 individuals ml−1. At the highest recirculation rate (daily water exchange of 500%) the highest rotifer production (2800 individuals per milliter in 11 days) was obtained after adjustment of the feeding scheme. This adjustment was necessary to compensate for food losses in the recirculation system. The use of a modified culture Selco (CSH) could further improve the performance of the rotifers. Using this experimental diet, a rotifer density of 8000 individuals per milliter could be obtained in 8 days without rinsing and restocking during the production period. When the rotifer populations were kept below their maximal density by daily harvests the culture period could be extended to more than 1 month. During this period the cultures were not subjected to any water exchange or restocking except the replacement of the water to compensate for the daily harvested rotifers (±20% of the standing population). In general terms it can be stated that the use of a recirculation system has proved to reduce labour and maintenance cost while ensuring stable physico-chemical rearing conditions resulting in more reliable and healthy rotifer cultures.

Monitoring of the evolving diversity of the microbial community present in rotifer cultures

Abstract The genetic fingerprint of the microbiota in the culture water of two different rotifer culture systems (batch versus recirculation) was obtained by means of denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. The genetic profile of the bacterial community present in the culture water of a batch culture system changed daily due to shifts occurring at the level of the dominance of bands. By means of statistical tools, it was possible to distinguish three different periods during the development of the microbiota in the recirculation experiment, each corresponding to a typical period during the production of rotifers. Overall, it was obvious that the microbiota in such a recirculation system was less susceptible for variation relative to the microbiota in a batch system. However, some shifts in the genetic profile were observed when technical problems occurred resulting in a reduced water quality or performance of the biofilter. Characterisation of the microbial community present in the recirculation system indicated that the sequences of typical bands showed the highest level of identity to the sequences from the bacterial strain MMB-1 T (representing a species in the genus Marinomonas , Marinomonas mediterranea sp.), M. vaga and Pseudoalteromonas haloplanktis spp. tetraodonis strain IAM 14160 (98%).

Production and application of on‐grown Artemia in freshwater ornamental fish farm

Abstract This paper describes a pilot culture system for the production of on‐grown Artemia in freshwater ornamental fish farms. The system had 21 culture units, each consisting essentially of three components: an oval‐shaped raceway, an air‐water lift system and two waste collectors. Using artificial seawater at 20 ppt for culture and at a mean production rate of 3 kg/m3 of water in a 12‐day cycle, the system had a production capacity of 8 metric tons of on‐grown Artemia a year. Biochemical analyses were preformed to evaluate the nutritional value of the on‐grown Artemia against three conventional live feeds, viz. live Artemia nauplii, live Moina and frozen bloodworms. Cost‐benefit analysis showed that with a capital investment of US