Red drum Sciaenops ocellatus growth and expression of bile salt-dependent lipase in response to increasing dietary lipid supplementation.

Sciaenops ocellatus has a long history in aquaculture and many difficulties associated with its commercial culture have been addressed and successfully resolved; nevertheless, further research in lipid nutrition could address more comprehensive questions on the way these nutrients are utilized. The purpose of this study was to evaluate S. ocellatus growth and lipase gene expression in response to increasing dietary lipid supplementation. Four experimental diets were formulated to provide 3, 10, 16, or 23% lipid using menhaden fish oil. Twenty juveniles (mean initial weight 2.3 ± 0.1 g) were stocked per aquaria in a recirculating system; each diet was assigned to three aquaria and fed to fish for 6 weeks. At the end of the study, fish fed 3% of dietary lipid were significantly (P < 0.0001) smaller and showed significantly lower feed efficiency, condition factor, hepatosomatic index, and intraperitoneal fat than fish fed the other diets, but no differences were observed among fish fed 10, 16, or 23% lipid. A straight broken-line regression model for thermal growth coefficient provided an estimated value of 9.4% of dietary lipid as the optimal inclusion level. The bile salt-dependent lipase (BSDL) of red drum was 80.3 kDa. Relative gene expression of BSDL was significantly higher (P = 0.0007) in fish fed 10% lipid, with no differences among the other dietary treatments. Results provided could help monitor the metabolic status of farmed fish and contribute to optimize diet formulations based on maximum gene expression of BSDL for supplementation of dietary lipid.

Effect of dietary protein source and time on alkaline proteolytic activity of Nile tilapia (Oreochromis niloticus).

A 4 x 3 factorial study was conducted to evaluate the effect of four experimental diets (a control diet and a 0, 50, and 100% fish meal replacement diet) and the period of time Nile tilapia, Oreochromis niloticus, were fed those diets (0, 20, and 40 days) on the alkaline proteolytic activity of the animals' digestive tract, as well as their potential interaction. Significant differences (at P < 0.05) and a significant interaction were observed among dietary treatments for the alkaline proteolytic activity of tilapia after 40 days of feeding. This study confirmed that, under these experimental conditions, a 50% fish meal replacement formulation elicited the highest alkaline proteolytic activity in the digestive tract of tilapia, which resulted in the highest final weight and specific growth rate (SGR), but further research is needed to establish the relative contribution of the alkaline proteases to the overall proteolytic activity of this omnivorous fish species.

Nutritional value of various ray fish liver oils to the pacific white shrimp Litopenaeus vannamei.

A 32-day comparative feeding trial was performed to evaluate the nutritional value of four different ray fish liver oils to the Pacific white shrimp Litopenaeus vannamei. Four feeds were prepared with liver oil extracted from Dasyatis brevis, Rhinoptera steindachneri, Aetobatus narinari, and R. bonasus. A control feed was prepared with Menhaden fish oil. Ray fish liver oils were mainly composed of poly- and highly unsaturated fatty acids and contained levels of 20:5n-3 and 22:6n-3 comparable in magnitude to those of Menhaden fish oil, except for A. narinari liver oil, which had moderately low concentrations of 20:5n-3 and 22:6n-3 but showed a particularly high level of 20:4n-6, more than six times greater than that of Menhaden fish oil. Dietary fatty acids significantly influenced the fatty acid composition of shrimp muscle tissue, e.g., the diet with Menhaden fish oil elicited significantly higher shrimp muscle DHA level than diets with oil from D. brevis, and A. narinari, but not than diets with oil from R. steindachneri and R. bonasus. In spite of these differences, all four ray fish liver oils evaluated were as efficient in promoting growth and survival of L. vannamei as Menhaden fish oil, an ingredient known for its adequate nutritional quality to shrimp and fish. This study demonstrated one of the many possible applications of a locally-available resource that is currently being wasted.