Optimization of dietary protein and lipid levels for butter catfish, (Ompok bimaculatus) (Bloch, 1794) fingerlings: An appraisal on growth, body composition, digestive enzymes, and metabolic function

ABSTRACT A completely randomized 3 × 3 factorial feeding trial was conducted to evaluate the effects of dietary protein and lipid levels on growth, feed utilization, body composition, and digestive as well as metabolic enzymes of the butter catfish (Ompok bimaculatus) fingerlings. Fish (average weight 0.66 ± 0.12 g; 30 d) were fed nine experimental diets containing three protein levels (35%, 40%, 45%) and three lipid levels (5%, 10%, 15%) in triplicate groups for a period of 90 days. The formulated diets were named P35L05, P35L10, P35L15, P40L05, P40L10, P40L15, P45L05, P45L10, and P45L15 (P = Protein; L = Lipid) respectively. The results indicated no protein-sparing effect of lipid in O. bimaculatus fingerlings beyond 35% dietary protein. Overall, diets P40L5 and P35L10 had significantly (P < 0.05) higher SGR (% day−1) and lower FCR than other experimental groups. The highest weight gain (10.89 ± 0.07 g) and carcass protein (16.71 ± 0.2%) were recorded in fish fed diet P40L05. Increasing dietary lipid levels brought about an increase in carcass lipid in fish. Activities of α-amylase and acid-protease were decreased (except at 5% lipid), whereas alkaline-protease was increased with increasing dietary protein. An increase in pyruvate kinase (PK, glycolytic enzyme) activity and decrease in glucose-6-phosphate dehydrogenase (G6PD, lipogenic enzyme) activity were noticed with increasing dietary lipid content. A decrease in PK and increase in G6PD activities were observed with increasing dietary protein levels. Activities of the gluconeogenic enzymes (glucose-6-phosphatase, fructose-1,6-phosphatase) increased significantly (P < 0.05) with increasing dietary protein and lipid levels. Amino acid catabolizing enzymes, alanine transaminase and aspartate transaminase, were slightly increased with increasing dietary protein levels. Considering growth, body composition, metabolic function, and survivability (>95%), the diet containing 40% crude protein with 5% lipid might be suggested as optimum for O. bimaculatus fingerlings under the tested conditions.