This study investigated the effects of graded dietary lysine levels on growth performance, hematobiochemical parameters and antioxidant capacity in two strains of African catfish (Clarias gariepinus), local and improved. Six isonitrogenous and isocaloric diets (35% crude protein and 460 kcal/100 g dm digestible energy) with lysine levels of 1.12% (control), 1.30%, 1.53%, 1.75%, 1.91%, and 2.20% were fed to triplicate groups of fingerlings (initial weight: 2 g) for 12 weeks in a flow-through system.
Lysine supplementation significantly enhanced growth performance, feed intake, and feed conversion ratio (p < 0.05), with survival unaffected. Peak weight gain occurred at 1.53–1.75% lysine for the local strain and 1.75–1.91% for the improved strain. Hematobiochemical and antioxidant indices improved with lysine supplementation, while aspartate and alanine aminotransferase activities decreased significantly at 1.75% and 1.91% lysine for local and improved strains, respectively. The improved strain demonstrated superior growth and a higher lysine requirement, indicating that genetic improvement influences amino acid needs. These results provide critical insights for optimizing lysine levels in strain-specific diets, supporting sustainable and efficient aquaculture of African catfish.