Effects of dietary protein and lipid levels on growth and body composition of sunshine bass ( Morone chrysops X M. saxatilis) reared in cages

Juvenile sunshine bass with an average weight of 125 g were stocked into 24 floating cages (1.2 × 1.2 × 2.4 m) and fed one of 8 practical diets formulated to contain various percentages (30, 36, 42, and 48%) of protein. Due to differences in composition of feed ingredients, diets were analyzed as having 29, 36, 41, and 46% protein. Each protein level was formulated with two lipid levels: low (between 6.5 and 9.8%) and high (between 13.3 and 17.1%). Fish meal composed a constant percentage (56%) of the dietary protein in all diets. Fish were stocked at a rate of 200 per cage and fed twice daily at 08.00 and 16.30 h. Fish were fed all they would consume in 30 min for approximately 150 days. Percentage weight gains and specific growth rates (SGR) of fish fed diets containing 41 and 46% protein (99 and 116 mg protein/kcal, respectively) were higher ( P < 0.05) than fish fed diets containing 29 and 36% protein, 67 and 82 mg protein/kcal, respectively. No differences ( P > 0.05) in survival or feed conversion ratio (FCR) were found among treatments. Percentage dress-out, abdominal fat, hepatosomatic index, and body composition of sunshine bass was affected by dietary protein and energy level ( P < 0.05). Percentage protein and lipid in carcass and waste (head and viscera) of fish fed diets containing 116 mg protein/kcal had higher ( P < 0.05) protein levels and lower lipid levels than fish fed diets containing 67 and 82 mg protein/kcal. These data suggest that juvenile sunshine bass require a diet containing 41% protein, or a protein to energy ratio greater than 99 mg protein/kcal, when fish meal comprises 56% of the dietary protein.