Effects of Replacing Fish Meal with Poultry By-Product Meal on Growth, Physiological Status, Disease Resistance, and Hepatic Transcriptomic Responses in Hybrid Yellow Catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂)

Purpose: This study evaluated the effects of replacing dietary fish meal (FM) with poultry by-product meal (PBM) on growth, physiological status, disease resistance, and hepatic transcriptomic responses in hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂). Methods: Six isonitrogenous and isolipidic diets were formulated by replacing 0%, 12%, 24%, 36%, 48%, or 60% of dietary FM with PBM. Juveniles (initial weight 5.18 ± 0.02 g) were fed the experimental diets for 8 weeks. Results: Weight gain was maximized and the feed conversion ratio minimized in fish fed the FM19 diet, with broken-line regression analysis of weight gain estimating the optimal FM replacement level at 27.4%. Hepatic and intestinal superoxide dismutase activities, as well as intestinal trypsin activity, tended to decline as the level of FM replacement with PBM increased. Following Edwardsiella ictaluri challenge, 96-h cumulative survival was lower in the FM10 group than in all other groups. Principal component analysis of hepatic transcriptomes clearly separated the FM10 group from the FM25 and FM19 groups. Gene Ontology analysis associated differentially expressed genes with responses to hormones and endogenous stimuli (FM10 vs. FM25), protein folding and chaperone-mediated complex assembly (FM19 vs. FM25), and catabolic processes and mitochondrial function (FM10 vs. FM19). Kyoto Encyclopedia of Genes and Genomes analysis identified pathways involving mitogen-activated protein kinase signaling, protein processing in the endoplasmic reticulum, autophagy, apoptosis, and inflammatory responses. Moreover, genes associated with oxidative stress and inflammation showed higher expression in the FM10 group compared with the FM19 and FM25 groups. Conclusions: Moderate FM replacement with PBM improved growth and feed utilization, whereas excessive replacement was associated with lower antioxidant and digestive enzyme activities, altered metabolic responses, and enhanced expression of inflammation-related genes, supporting PBM as a partial FM substitute in low-FM diets for hybrid yellow catfish.