In vivo protein synthesis rates in larval nase (Chondrostoma nasus L.)

In vivo protein synthesis rates were determined in larvae of nase (Chondrostoma nasus (L.)) by bathing the fish in [3H]phenylalanine. After a delay of about 1 h the rate of labelling of the larval protein was linear. A significant relationship was found between specific growth rate (kg) and fractional rate of protein synthesis (ks) when animals from low and high ration groups and starved animals are included, which can be described by ks = 8.5 + 1.45 kg (both variables in %∙day−1). The efficiency of retention of synthesised protein (kg∙100/ks) was 45% at a growth rate of 10%∙day−1 and 50% at 15%∙day−1. The metabolic costs of total protein synthesis were estimated by comparing the protein synthesis rates of C. nasus with levels of oxygen consumption in similarly treated larvae of the related species Rutilus rutilus. At growth rates below 10%∙day−1, oxygen consumption above maintenance (FIT, food induced thermogenesis, μmol O2∙g fresh weight−1∙h−1) is related to protein synthesis (Ps, mg protein synthesised∙g fresh weight−1∙h−1) by FIT = 24.7 Ps − 3.3. This relationship provides an estimate of the cost of protein synthesis of 24.7 μmol O2 ∙ mg protein synthesised−1 which is 3 times higher than minimal theoretical costs.