Corn Peptide: From By-Product to Functional Feed Ingredient—Application Evaluation in the Diets of Juvenile Tiger Puffer (Takifugu rubripes)

This study evaluated the effects of replacing fish meal (FM) with corn peptide (CP) in juvenile tiger puffer in indoor tanks. Four diets were formulated for a 53-day feeding trial: a control group (CP0), and diets with 5% (CP5), 10% (CP10), and 15% (CP15) CP replacing FM. Each diet was fed to triplicate tanks. No significant difference in weight gain was observed between CP5 and control (p > 0.05). However, when the CP inclusion level exceeded 10%, growth performance began to decline, with the CP15 group being significantly lower than the control. The feed intake was linearly increased by CP. The proximate body composition revealed no significant difference among treatments. The CP10 group showed significantly higher serum malondialdehyde content than the control. Significantly lower muscle fiber density was observed in CP10 and CP15 compared to the control. The taurine content was significantly reduced in CP10, while no significant differences were found for other amino acids. Compared with the control group, the CP5 group showed significantly elevated levels of free proline and glutamic acid. The intestinal expression of the peptide transporter gene pept1 was significantly up-regulated by CP. In conclusion, the appropriate inclusion level of corn peptide was 5% for juvenile tiger puffer.