Fish protein hydrolysates have been used in the past as a source of protein in larval fish diets with various success. This study looked at utilizing same-species muscle and endogenous enzymes to produce a fish muscle hydrolysate for inclusion in larval dry diets. Specifically, the objective of this study was to determine the effect of the source of muscle and endogenous enzymes on the hydrolysis of fish muscle and its impact on; 1) growth performance and survival; 2) the occurrence of skeletal deformities; 3) gene expression of intestinal peptide transporter PepT1; and 4) the muscle FAA pool used as an indicator of dietary amino acid availability; in larval Walleye.
Four different hydrolysates were produced for this study, two obtained from Walleye muscle, one hydrolyzed with Walleye and another one with Tilapia endogenous enzymes. The other two hydrolysates were obtained from Tilapia muscle, hydrolyzed with either the Walleye or Tilapia endogenous enzymes. The muscle and enzymes were mixed continuously during the hydrolysis (at 22oC and 28oC for Walleye and Tilapia enzymes, respectively), and the pH was adjusted throughout the process to mimic stomach and intestinal digestion conditions. At 4 dph, larval Walleye were randomly distributed into 18 (280 L) tanks, with ~2000 fish per tank. There were 6 treatment groups in this study, with 3 replicates. Each group was fed to satiation for 3 weeks. The Artemia group was fed Artemia nauplii for the entire duration of the study. The rest of the groups received a dry diet supplemented with Artemia during the first 3 days. The Otohime group was fed with a commercial diet, and the other four groups were fed diets that contained a 50/50 level of intact protein and hydrolyzed protein produced from Walleye muscle, hydrolyzed with Walleye (W-W) or Tilapia (W-T) endogenous enzymes, or Tilapia muscle, hydrolyzed with Walleye (T-W) or Tilapia (T-T) endogenous enzymes.
The results showed that the group fed with the Walleye muscle hydrolysate, produced with Walleye endogenous enzymes, had a significantly higher average weight at the conclusion of the study, compared to all other groups (Figure 1). This result provides support for the use of protein hydrolysates produced with same-species muscle and endogenous enzymes, for inclusion in larval fish diets. The results on PepT1 expression, FAA composition, and skeletal deformities will be presented in the oral presentation.