Response of Atlantic croaker fingerlings to practical diet formulations with varying protein and energy contents

Atlantic croaker Micropogonias undulatus is a demersal marine species that is heavily utilized as both a bait and food fish, and which may have commercial culture potential as a bait species. This research sought to initiate the development of practical diet formulations for juvenile growout and to evaluate the response of this species to controlled culture conditions. Eight practical diets were formulated to evaluate the effects of: 1) increasing lipid levels in a 45% protein diet; 2) dietary protein levels of 45, 40, 35 and 30%; and 3) progressive reduction in dietary energy content of diets with 30% protein. Each diet nas offered to four replicate groups of fish having a mean initial weight of 3.8 g over a 7-wk growth trial. At the conclusion of the trial, final mean weights ranged from 17.0 g (410% weight gain) to 8.1 g (210% weight gain) with 100% survival for al dietary treatments. Weight gain and feed efficiency increased with protein content of the diet, with fish fed the 45% protein diet performing the best. Weight gain of fish maintained on the 45% protein diet decreased, but not significantly, as the Lipid content of the diet was increased from 8 to 12 or 16%. Feed efficiencies for fish maintained on the diet containing 8% lipid were significantly higher than that of fish maintained on the diet containing 16% Lipid. In low protein diets, the replacement of wheat starch with indigestible fiber did not significantly influence growth or feed utilization, indicating that high levels of digestible carbohydrate were not well utilized as an energy source by the fish. The observed results would indicate that growth is optimized on a high protein diet with moderate lipid levels.