Protein synthesis in gilthead sea bream: response to partial fishmeal replacement

The present study aimed to measure tissue protein synthesis in sea bream fed isonitrogenous diets that contained 63, 55 and 50 % fishmeal; in the latter two diets, 16 and 27 % of the fishmeal protein was replaced with plant protein. Over a 35 d period, there were no differences in feed intake, growth or feed efficiency among the three diets. Protein metabolism was then measured in the liver and white muscle tissue as rates of protein synthesis and as the capacity for protein synthesis before feeding (0 h) and at different times after feeding (4-48 h). Diet did not have a significant effect on protein synthesis or on the capacity for protein synthesis in either tissue. The capacity for protein synthesis was not affected by time after feeding, and overall mean values were 81·02 (se 1·68) and 4·07 (se 0·94) mg RNA/g protein for the liver and white muscle, respectively. Liver and white muscle fractional rates of protein synthesis were significantly higher at 4-8 h, intermediate at 12 h and were not different among pre-feeding (0 h), 24 and 48 h. Overall, the indices of protein metabolism measured at various times over 48 h following feeding were closely aligned with measurements of feeding, growth and growth efficiency established over a longer time scale.