Effect of dietary carbohydrate to lipid ratios on growth, digestive enzyme and blood metabolites of juvenile Brazilian sardines, Sardinella brasiliensis (Steindachner, 1879)

The limited availability of live bait for capturing skipjack tuna, Katsuwonus pelamis, is a bottleneck to increasing tuna production in many parts of the world. Therefore, a nutrition trial was performed to contribute to the production of the Brazilian sardine, Sardinella brasiliensis, for use as live bait. This study determined the best dietary carbohydrate to lipid ratio (CHO:L) for juvenile Brazilian sardines based on growth performance, feed utilisation, body composition, blood metabolites and digestive enzyme activity. Six isoenergetic and isonitrogenous diets were formulated with increased CHO:L ratios (2.05, 3.41, 4.15, 5.11, 5.80 and 6.72). Each diet was randomly assigned to triplicate groups of 100 fish with mean initial body weight of 2.97 +/- 0.51g, which were fed four times a day to apparent satiation. Survival was not affected by differences in diet, however, a low CHO:L ratio stimulated growth. Juveniles fed with a rich-carbohydrate diet inhibit feed intake and protein intake. Body lipid increased as dietary lipid increased and was inversely correlated to body moisture. The diets did not affect the juvenile's blood metabolites. Alkaline and acid protease activities were not significantly different, but lipase and amylase responded positively to the dietary lipids and carbohydrates. Using segmented regression, the optimum CHO:L ratio for maximum weight gain of juvenile Brazilian sardines was estimated to be 3.41, which contain approximately 300gkg(-1) carbohydrate and 88gkg(-1) lipid.