The effect of protein to lipid ratios on growth, digestibility, and feed utilization of striped bass (Morone saxatilis) raised in seawater at 21°C

Abstract

A 12-week feeding trial was conducted to assess the effects of three protein levels (40%, 44%, and 48%) and two lipid levels (12% and 16%) on growth, feed utilization, muscle composition, apparent digestibility, and digestive enzyme activity of juvenile striped bass (Morone saxatilis) raised in seawater at 21°C. The results showed that performance in terms of specific growth rate (SGR), weight gain (g), and feed conversion ratio (FCR) were significantly higher (p < 0.05) for fish fed the 44:12 and 48:12 diets. These treatments also exhibited significantly higher feed intake. In contrast, fish fed the high-lipid diets exhibited significantly lower fed intake, hepatosomatic index (HSI), liposomatic index (LSI) and viscerosomatic index (VSI) compared to the low-lipid diets. Furthermore, significantly higher apparent digestibility coefficients (ADC %) were found for fish fed diets containing 12% lipids. A positive correlation was also observed between feed intake and the activity of trypsin (r = 0.56, p < 0.05) and chymotrypsin (r = 0.50, p < 0.05) in the pyloric caeca of the fish. Lipid content in muscle at the end of the feeding trail was not significantly affected by dietary lipid level. In conclusion, the results indicate that a diet with 48% protein and 12% lipids stimulates growth, increases feed intake, digestibility and enhances feed utilization in juvenile striped bass. Based on the results from the present study we can recommend formulating diets with a E:P ratio of 7.4 kcal/g of crude protein diet and not to exceed 8.2 kcal/ g of protein.