Effects of Dietary Lipid Levels on Growth Performance and Transport Stress Tolerance in Channel Catfish (Ictalurus punctatus)

This study aimed to investigate the effects of dietary lipid levels on growth performance and transport stress resistance in large-sized channel catfish (Ictalurus punctatus). Four experimental diets were formulated with fat levels of 7.5% (control), 10.0%, 12.5%, and 15.0%, using soybean oil as the lipid source. Each diet was assigned to four replicate groups in a 110-day feeding trial, with fish averaging 600.61 ± 1.33 g at the start. Results showed that increasing dietary fat enhanced weight gain rate (WGR) and specific growth rate (SGR), with the 15.0% fat group achieving the best growth performance and the lowest feed conversion ratio (FCR), significantly lower than the control (p < 0.05). However, fish fed diets containing 12.5% and 15.0% fat exhibited disorganized hepatocyte arrangement, unclear cell boundaries, and hepatic vacuolization. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities increased initially and then declined with rising fat levels, with the highest values observed at 12.5% fat, significantly exceeding those in the control group (p < 0.05). Furthermore, after simulated transport, the incidence of skin congestion and hemorrhage increased with dietary fat level. Collectively, while higher fat levels improved growth, excessive fat (≥12.5%) compromised liver health and stress resilience. Therefore, a dietary fat level of 10.0% is recommended to balance optimal growth, hepatic integrity, and transport tolerance in I. punctatus.