Organic Selenium Improves Growth Performance and Metabolic Biomarkers in African Catfish (Clarias gariepinus Burchell, 1822) Fed Fishmeal-Free Diets

Raw material cost including protein sources account for at least 70% of total aquafeed production cost. Protein is among the top three most expensive nutrients to supply in aquaculture diets, after energy and phosphorus. It is imperative to identify effective and practical strategies to ensure that African catfish (Clarias gariepinus; Burchell, 1822) utilizes amino acid intake for optimum growth. The ever-increasing cost-price squeeze between aquaculture input costs and output prices have forced aquafeed to reduce dietary nutrient specifications particularly amino acids. This occurs against a backdrop of sustainability concerns regarding fish meal as a protein source. This work studied 450 C. gariepinus in 15 experimental aquariums for a 62-day culture period. Implementing an experimental design with five fish meal-free dietary treatments and three replicates, differing in organic selenium content, Se0.5 (0.5 ppm), Se2 (2.0 ppm), Se4 (4.0 ppm), Se6 (6.0 ppm) and Se8 (8.0 ppm). Se4 achieved the highest final biomass at 2092.97g (P>0.05) and ADG at 34.79 g/day/aquarium (P<0.05). The superior performance was supported by favorable metabolic biomarkers, showing highest expression of the igf1 gene at 2.75 (P<0.05), avoided hyperglycemia with blood glucose maintained at 33.67mg/ dL (P<0.05), hepatosomatic index of 1.85 (P<0.05) and highest body selenium retention at 18.53% (P<0.05). Selenium supplementation exerted a positive effect on C. gariepinus energy metabolism. In conclusion, practical African catfish diets can implement the 4.0mg/ kg organic selenium supplementation regime to achieve optimum growth and enable cost-saving lower protein diets.