The influence of dietary protein and energy levels on growth, survival and thyroid hormone (T3 and T4) composition of Lates calcarifer larvae

Two growth trials were conducted to determine the effects of different dietary protein (450–550 g kg−1) and energy contents (18–22 MJ kg−1) on growth, survival and carcass thyroid hormone (T3 and T4) levels of barramundi (Lates calcarifer) larvae. Larvae fed diets containing 21 and 22 MJ kg−1 dietary energy performed consistently better than those fed diets containing 18 and 19 MJ kg−1 dietary energy in terms of final dry weight and total length, while those fed 20 MJ kg−1 had intermediate values for both the parameters. No effects of dietary protein level were discernable from the physical parameters measured; however, larvae fed diets containing the lowest protein and energy combination (450 g kg−1 protein/18 MJ kg−1 energy) had significantly lower carcass T4 levels than larvae in all other treatments, except for those fed the 500 g kg−1 protein/18 MJ kg−1 diet, which had an intermediate value. The results indicate that the optimum diet for L. calcarifer larvae from 14 to 28 days after hatch should contain 500 g kg−1 protein and a minimum of 21 MJ kg−1 dietary energy. Carcass T4 content was influenced by macronutrient inclusion level, and correlated significantly with growth, described by the total length. Reduced T4 levels may indicate a depressed larval status in this species

Role of thyroid hormones in tilapia larvae (Oreochromis mossambicus): II. Changes in the hormones and 5′-monodeiodinase activity during development

10.1007/BF02274229Fish Physiology and Biochemistry95-6487-496FPBI