Advances in rearing cobia Rachycentron canadum larvae in recirculating aquaculture systems: Live prey enrichment and greenwater culture

Abstract

Cobia Rachycentron canadum is a relatively hardy species which exhibits high rates of growth during the larval and juvenile periods. Currently, this species is considered to be a good candidate for commercial production in recirculating aquaculture systems. However, little information is available regarding the nutritional requirements of cobia larvae in such systems, and this information is required to advance commercial technologies for the successful production of cobia fingerlings. Experiments were conducted to examine the effects of enriching rotifers and Artemia with live algae or commercial preparations on the growth and survival of cobia R. canadum larvae and to evaluate the benefits of adding live algae to the systems. Prey items were enriched with live Isochrysis galbana, live Nannochloris oculata, Algamac 2000, Algamac 2000 supplemented with 10% or 20% Aquagrow arachidonic acid, or Algamac 3050. In addition, larvae fed prey enriched with Algamac 2000 were reared in the presence of live I. galbana (∼ 40,000 cells ml − 1) or N. oculata (∼ 80,000 cells ml − 1). Significant differences in the fatty acid composition of the rotifers and Artemia were found among treatments. Generally, prey enriched with the commercial preparations contained higher levels of highly unsaturated fatty acids than those enriched with live algae. Furthermore, a positive correlation was found between dietary docosahexaenoic acid (DHA) and the amount of DHA measured in the whole body tissues of 16-day-old larvae. Larval growth (measured as standard length) and survival of 16-day-old larvae were significantly higher ( P < 0.05) when larvae were fed prey enriched with the commercial preparations (14.7–15.2 mm; 12.0–15.6%) compared to N. oculata (11.8 mm; 4.4%). However, when larvae were reared on N. oculata enriched rotifers and subsequently fed Algamac 2000 enriched Artemia there were no significant differences in growth or survival compared to larvae which were fed both rotifers and Artemia enriched with Algamac 2000. This suggests that the enrichment of rotifers may be less important than the enrichment of Artemia. No significant differences in growth or survival were found when larvae were fed prey enriched with live I. galbana (13.5 mm; 8.2%) or commercial preparations (12.4–12.6 mm; 12.9%). However, the presence of live algae ( I. galbana or N. oculata) in the rearing tanks significantly improved larval survival to 23.3% and 24.7%, respectively. The results of this study suggest that enriching rotifers and Artemia with live I. galbana or commercial preparations such as Algamac 2000 and 3050 in conjunction with greenwater culture systems improves the growth and survival of cobia larvae in recirculating aquaculture systems.