REASSESSING THE LYSINE REQUIREMENT OF JUVENILE LARGEMOUTH BASS Micropterus salmoides  

The commercial production of largemouth bass (LMB), Micropterus salmoides, for food has expanded in recent years entailing the development of cost-effective diets for this species; however, limited data exists pertaining to the amino acids (AAs) requirements of this species. Therefore, the objective of this study was to reassess the dietary lysine (Lys) requirement of juvenile LMB.

A basal diet was formulated to contain the AA profile of a 40% crude protein LMB muscle and 12% lipid.  Protein-bound AAs in the basal diet were derived from sardine fishmeal included at 20% and providing 1.04% Lys. Five additional diets were designed to contain incremental amounts of crystalline L-Lys (as Lysine HCl, 78% L-Lys) ranging from 1.46 to 2.83% of the diet.  Lys inclusions to the basal diet were performed at the expense (N basis) of L-aspartate and L-glutamate. LMB juveniles (270; average weight 9.8±0.5g) were stocked into 18 110-L glass aquaria (15 per tank) in a closed recirculating system. Fish were fed the experimental diets (three replicates per diet) to apparent satiation twice daily for 8 weeks. At the end of the experiment, fish in each aquarium were group weighed and sampled for blood chemistry and physiological parameters, condition indices, whole-body and muscle proximate and AA compositions.

After 8 weeks of feeding, survival of LMB ranged from 82 to 98%. Blood analyses indicated a significant effect of dietary Lys on hematocrit and hemoglobin. Using regression analysis, the Lys requirement for optimizing thermal growth coefficient (TGC, Figure), weight gain, and feed efficiency was estimated to range from 1.90 to 2.01% of the LMB diet.