Effect of Diet and Strain on Growth and Performance in Hybrid Bluegills

Abstract

Little is known about the diets and genetic strains that are optimal for the production of hybrids of bluegill Lepomis macrochirus. The objective of this study was to determine whether there are differences in feed, nitrogen and amino acid conversion, lipid deposition, liver lysine oxidation, and liver glycogen in two such hybrids—Georgia Giant (GG, a proprietary strain of hybrid bluegill) and a commercial hybrid bluegill (CHBG, green sunfish L. cyanellus × bluegill)—fed five commercially available diets. The diets were formulated to the following minimum crude protein (CP)–fat ratios: 32/3, 38/8, 40/10, 42/16, and 45/20. Fish were randomly allotted to 20 tanks, with two tanks per diet within each strain. After 12 weeks in experimental conditions, GGs had higher feed intake (P < 0.001), higher weight gain (P < 0.001), better feed conversion (P < 0.05), and lower liver glycogen (P < 0.05) than CHBG. Liver lysine oxidation and whole-body lipid deposition was not significantly different between strains. Consumption of the 42/16 diet resulted in increased growth, a better feed conversion (P < 0.05), and a better retention of specific amino acids than all other diets, regardless of strain. Diet composition did not result in significant differences in liver lysine oxidation, liver glycogen, and lipid deposition, regardless of strain. These data demonstrate that genetic strain and diet have important impacts on bluegill production and that the most nutrient-dense diets do not necessarily lead to enhanced performance relative to diets of lower CP and fat.