Hydrolyzed Feather Meal in Diet of Yellow Catfish ( <i>Pelteobagrus fulvidraco</i> ): Effects on Growth Performance, Flesh Quality, Skin Color, and Intestinal Flora

An 8-week feeding trial was conducted to assess the effects of hydrolyzed feather meal (HFM) as a fish meal replacement on the growth performance, flesh quality, skin color, and intestinal microbiota of yellow catfish (<i>Pelteobagrus fulvidraco</i>). Five isonitrogen (44% crude protein) and isolipidic (8.5% crude lipid) diets were formulated with varying levels of HFM at 0% (FM, control), 2.05% (HFM2), 4.10% (HFM4), 6.15% (HFM6), and 8.20% (HFM8), corresponding to fish meal replacement of 0%, 8.33%, 16.67%, 25%, and 33.33%, respectively. Results indicated that the growth performance declined significantly as HFM inclusion increased. Based on the results of weight gain rate (WGR) and specific growth rate (SGR), the maximal replacement levels of fish meal with HFM for yellow catfish should be 16.67%. Intestinal enzyme activities, including trypsin, lipase, amylase, and Na⁺-K⁺-ATPase as well as villus height, muscular thickness, and goblet cells number were significantly enhanced in HFM groups. Fish meal replacement with HFM remarkably reduced serum immune indicators acid phosphatase, immunoglobulin M, Complement 3, and Complement 4 levels and significantly increased serum aspartate aminotransferase, total triglycerides, and cholesterol levels, indicating compromised immune function and liver health. The content of collagen and flavor-enhancing amino acids (glutamic acid [Glu], glycine [Gly], and alanine [Ala]), as well as muscle hardness were distinctly boosted, demonstrated an elevated flesh texture led by dietary HFM inclusion. The abnormal skin coloration induced by pigmentary disorders was observed in high HFM inclusion groups, the black pigmentation on dorsal and yellow pigmentation on the abdomen exhibited a gradual reduction in intensity. The study found that replacing up to 16.67% of fish meal with HFM in yellow catfish diets maintained growth performance and improved meat quality. However, high HFM levels damaged serum immune system and caused liver dysfunction, dyslipidemia, pigmentary disorders, and reshaped intestinal microbial structure.