This study aimed to provide an efficient protein source for larval fish by using same-species muscle and endogenous enzymes to produce hydrolysates and, provid ing a series of diets with increasing molecular weight protein fragments through larval development. The objective of this study was to determine the effect of the degree of hydrolysis of Largemouth Bass (LMB) muscle protein obtained using LMB digestive tracts when used in first feeds for larval LMB 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 composition.
Batches of fresh LMB muscle were hydrolyzed for 1.5, 3, and 6 hrs, respectively, in order to obtain hydrolysates containing protein profiles with differing molecular weights. The muscle was mixed with LMB endogenous enzymes obtained from whole fish digestive tracts at 25oC and the pH was adjusted to 3-4 and later to 7-9 to mimic LMB stomach and intestinal digestion conditions, respectively . Five diets were produced for this study, the intact diet containing non-hydrolyzed LMB muscle and four diets in which the intact muscle protein was replaced in 50% with LMB hydrolysates. Those four diets were characterized by their level of each hydrolysate (presented as ratio of 1.5, 3, and 6 hrs hydrolysates, respectively): 1:1:1, 1:3:6, 1:3:1, 6:3:1 for diets A, B, C, and D, respectively. At 4 days post hatch (dph), larval LMB were randomly distributed into 21 (280 L) tanks, with ~2000 fish per tank. There were 7 treatment groups in this study, with 3 replicate s, provided during 5-26 dph (Figure 1) .
No significant differences were detected in growth performance between the intact protein and hydrolysate fed groups, regardless of molecular weight profile . However, t he transition of hydrolysates with differing molecular weight profiles in the diets significantly reduced the occurrence of skeletal deformities in the larval LMB , compared to Hydro-A, which received the same hydrolysate diet throughout the entire experiment. These results provide support for the transition of the molecular weights of dietary protein throughout larval development, as a means of matching the absorption capacity of larval LMB. The results on PepT1 expression and FAA composition will be presented in the oral presentation .