The use of algal substitutes and the requirement for live algae in the hatchery and nursery rearing of bivalve molluscs: an international survey

The mass-production of micro-algae has been recognized by several authors as the main bottle-neck for the culture of bivalve seed. This has prompted a search for alternatives to on-site algal production, such as dried heterotrophically-grown algae, preserved algal pastes, micro-encapsulated diets, and yeasts. However the extent to which these products have been tried, and rejected or retained by hatchery operators is poorly documented. Also, the actual algal requirement and production cost of the bivalve seed industry is difficult to estimate.The present inquiry allowed the collection of data concerning the requirement of live algae and its associated costs encountered in 50 commercial and experimental hatcheries from all over the world. Furthermore, the hatchery operators were questioned about their experience with alternatives for live algae, the quality and quantity of hatchery produced algae and bivalve seed, and the employment of this sector in aquaculture.The capacity of the algal production facilities ranged between 1 m³ for a few research laboratories to nearly 500 m³ for one commercial hatchery. The total algal production capacity reported by 37 hatcheries amounted to about 500 m³ algal culture day-1, which is equivalent to about 50 kg of dry biomass. The total cost of algal production in 1990 reported by 20 hatcheries approximated US $700,000 and averaged about 30$50 to 400 per kg dry weight.About a third of the questioned operators considered algal production as a limiting factor in the rearing of bivalve seed, whereas over 50% planned an expansion of the algal cultures and more than 90% was interested in the use of suitable artificial diet. The large interest for alternatives for on-site algal production was further demonstrated by the fact that more than 50% of the operators claimed to have experimented with artificial diets. Despite the extensive research efforts, artificial diets are rarely applied in the routine process of bivalve seed production and are mostly considered as a useful backup diet

Lipid classes and their content of n-3 highly unsaturated fatty acids (HUFA) in <i>Artemia franciscana</i> after hatching, HUFA-enrichment and subsequent starvation

The distribution of n-3 highly unsaturated fatty acids (HUFA) over the major neutral and polar lipid classes was determined for two predominant types of live food used in the larviculture of marine fish and shrimp, i.e. freshly hatched and HUFA-enriched Artemia, and compared with data reported in the literature for wild copepods, representing the natural diet of these larvae. Lipid class composition and their content of n-3 HUFA, particularly eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3), were assessed in freshly hatched, HUFA-enriched and subsequently starved Artemia franciscana. The n-3 HUFA enrichment was based on feeding Artemia a lipid emulsion in which either fatty acid ethyl esters (EE, diluted with olive oil) or triacylglycerol (TAG) provided a level of 30% n-3 HUFA. Enrichment of Artemia with either type of the lipid emulsions resulted in an increase of total lipid content from 20.0 to 28.2-28.7% of dry matter mainly due to the accumulation of neutral lipid, primarily TAG (from 82 to 158 mg g(-1) dry wt in freshly hatched and 24-h enriched Artemia). Enriched brine shrimp utilized up to 27-30% of their TAG content during 72 h of starvation at 12 degrees C. The absolute tissue concentrations of polar lipids remained constant at 71 to 79 mg g(-1) dry wt throughout the enrichment and subsequent starvation. The level of n-3 HUFA increased drastically during enrichment from 6.3% of total fatty acids (8.2 mg g(-1) dry wt) in freshly hatched nauplii to between 20.4 and 21.8% (40.4 to 43.2 mg g(-1) dry wt) in 24-h enriched Artemia and was not significantly affected by the source of n-3 HUFA. During starvation, 18:0, 20:4n-6 and 20:5n-3 were retained, whereas 18:4n-3, 22:5n-3 and 22:6n-3 were specifically catabolized. The major polar lipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC), of freshly hatched Artemia showed very low levels of DHA ( 64% of the EPA and > 91% of the total DHA present. This is in sharp contrast with the high levels of n-3 HUFA, in particular DHA, in the polar lipid fraction reported for wild copepods. The contrasting distribution of DHA in the neutral and polar lipid fractions of enriched brine shrimp compared to the natural diet may influence the efficacy of this essential fatty acid for marine fish larvae in aquaculture systems

Effect of algal ration on feeding and growth of juvenile manila clam <i>Tapes philippinarum</i> (Adams and Reeve)

Juvenile Tapes philippinarum (Adams and Reeve) were reared for three weeks on different rations of Chaetoceros neogracile which were either centrifuged and stored or fed together with the culture medium. Algal rations were adjusted daily in order to feed constant weight-specific daily rations. Growth of T. philippinarum fed the concentrate of C. neogracile was maximal at a daily ration of 1% (algal dry weight per clam live weight). T. philippinarum fed single or mixed diets of C. neogracile and Isochrysis sp. (clone T-Iso) directly from the algal cultures, maximized growth at a ration of 1,3% day -1. Higher growth rates and gross growth rates efficiencies were obtained with C. neogracile fed together with the culture medium. A set of grazing experiments showed that the incipient limiting concentration was about 26 C. neogracile cells µ1-1. Measurements of cell concentration during the growth tests demonstrated a discontinuous feeding activity in the treatments receiving the optimal ration for maximum growth

Enhancement of Penaeus monodon shrimp postlarvae growth and survival without water exchange using marine Bacillus pumilus and periphytic microalgae.

We have investigated the possibility of using a consortium of marine bacterium and periphytic microalgae to improve the water quality and increase the growth and survival of the shrimp Penaeus monodon in a hatchery system. Three treatments were evaluated for their effect on P. monodon postlarvae (PL) when the culture water was not changed: Bacillus pumilus alone (B); periphytic microalgae alone (M); B. pumilus + periphytic microalgae (BM). P. monodon PL raised in a tank of unchanged water without bacterium and periphytic microalgae served as the control. The water in tanks of the M and BM treatments had significantly low levels of total ammonia-nitrogen (TAN) (0.03 and 0.01 mg l−1, respectively) and nitrite-nitrogen (NO2-N) (0.03, 0.01 mg l−1, respectively) than that in the B (TAN 0.80, NO2-N 0.68 mg l−1) and control (TAN 1.11, NO2-N 1.12 mg l−1) tanks. Moreover, PL cultured in tanks M and BM had significantly higher survival and specific growth rates and a significantly higher resistance to the reverse salinity stress test than those in the B and control tanks. Compared to the control PL, the PL cultured in the BM tanks had significantly higher levels of protein, lipid, polyunsaturated fatty acids, ecosapentaenoic acid, and docosahexaenoic acid. The culture water in tanks BM also contained significantly less Vibrio than the control water. Our results illustrate the beneficial effects of a B. pumilus and periphytic microalgae consortium on improving the water quality and the growth and survival of shrimp PL grown in a hatchery system

Fish oil replacement in current aquaculture feed : is cholesterol a hidden treasure for fish nutrition?

Teleost fish, as with all vertebrates, are capable of synthesizing cholesterol and as such have no dietary requirement for it. Thus, limited research has addressed the potential effects of dietary cholesterol in fish, even if fish meal and fish oil are increasingly replaced by vegetable alternatives in modern aquafeeds, resulting in progressively reduced dietary cholesterol content. The objective of this study was to determine if dietary cholesterol fortification in a vegetable oil-based diet can manifest any effects on growth and feed utilization performance in the salmonid fish, the rainbow trout. In addition, given a series of studies in mammals have shown that dietary cholesterol can directly affect the fatty acid metabolism, the apparent in vivo fatty acid metabolism of fish fed the experimental diets was assessed. Triplicate groups of juvenile fish were fed one of two identical vegetable oil-based diets, with additional cholesterol fortification (high cholesterol, H-Chol) or without (low cholesterol, L-Chol), for 12 weeks. No effects were observed on growth and feed efficiency, however, in fish fed H-Col no biosynthesis of cholesterol, and a remarkably decreased apparent in vivo fatty acid b-oxidation were recorded, whilst in LChol fed fish, cholesterol was abundantly biosynthesised and an increased apparent in vivo fatty acid b-oxidation was observed. Only minor effects were observed on the activity of stearyl-CoA desaturase, but a significant increase was observed for both the transcription rate in liver and the apparent in vivo activity of the fatty acid D-6 desaturase and elongase, with increasing dietary cholesterol. This study showed that the possible effects of reduced dietary cholesterol in current aquafeeds can be significant and warrant future investigations