A Novel Approach in the Development of Larval Largemouth Bass Micropterus salmoides Diets Using Largemouth Bass Muscle Hydrolysates as the Protein Source

SIMPLE SUMMARY: During the larval stage, Largemouth Bass rely heavily on the live feed. However, live feed culture is expensive to maintain, requires more labor, and is highly unpredictable. Dry diets would provide more nutritional control during the larval culture and be more cost-effective than live feed. Hence, live feed replacement has been a major focus of the aquaculture industry in the past decades. Larval Largemouth Bass is characterized by a highly underdeveloped gut, unable to efficiently digest complex dietary protein, and the amino acid requirements of larval fish in general are difficult to quantify. This study proposed the utilization of adult Largemouth Bass muscle as a protein source to provide the optimal amino acid composition for the larval fish of the same species. The muscle was also predigested with enzymes from the adult bass gut to produce protein that would be easier to digest by the primitive larval gut. Overall, the innovative protein did not improve the growth performance of the larval Largemouth Bass. Further research into determining the optimal protein source and its form is recommended to reduce the reliance on live feeds during the Largemouth Bass’ larval stage. ABSTRACT: This study’s objectives were to determine the effect of Largemouth Bass (LMB) muscle hydrolysates obtained using same-species digestive enzymes and the degree of LMB muscle hydrolysis when included in the first feeds of growth performance and survival, skeletal development, intestinal peptide uptake, and muscle-free amino acid composition of larval LMB. LMB muscle was mixed with digestive enzymes from adult LMB, and hydrolyzed for 1.5, 3, and 6 h, respectively. Five diets were produced, the intact diet containing non-hydrolyzed muscle and four diets with 37% muscle hydrolysate inclusion. Those diets were characterized by their level of each hydrolysate (presented as a ratio of 1.5, 3, and 6 Ts hydrolysates): 1:1:1, 1:3:6, 1:3:1, 6:3:1 for diets A, B, C, and D, respectively. To account for gut development, one group of larval LMB was fed a weekly series of diets B, C, and D to provide an increasing molecular weight profile throughout development. This group was compared against others that received either; (1) diets D, C, and B; (2) diet A; or (3) intact diet. The initial inclusion of the hydrolysates significantly improved the total length of the larval LMB; however, neither the hydrolysate inclusion nor the series of dietary molecular weight profiles improved the overall growth of larval LMB. The inclusion of hydrolysates significantly decreased the occurrence of skeletal deformities. The degree of hydrolysis did not have a significant effect on the parameters measured, except for intestinal peptide uptake, which was increased in the group that received the most hydrolyzed diet at the final time of sampling. The lack of overall growth improvement suggests that while the hydrolysates improve the initial growth performance, further research is necessary to determine the optimal molecular weight profile, hydrolysate inclusion level, and physical properties of feeds for larval LMB.