Protein synthesis in different tissues of mature rainbow trout (Salmo gairdneri R.). Influence of triploidy

1. The composition and protein synthesis rates of the liver, digestive tract, muscle, skin and remains were analysed in mature diploid (2.1 kg) and triploid (1.8 kg), 3 year-old rainbow trout reared at 8-degrees-C. 2. The lipid and DNA concentration of the digestive tract were respectively 16-17% and 30% higher in the triploids than in the diploids. 3. The DNA and RNA concentration in the other tissues were relatively similar between the diploids and triploids, except in the male gonad. 4. In vivo protein synthesis rates were measured using a single high dose injection of L-[U-C-14]-arginine (0.55 mmol/kg). 5. A small amount of radioactivity was found in the lipid of the whole trout (2-3% of the injected dose). 6. According to their mean Fractional Protein Synthesis Rates (FSR) of protein, tissues were ranked as follows: liver (1.6-44%.d-1), male gonads (12-30%.d-1), digestive tract (7-9%.d-1), skin (5%/d), carcass (0.4-0.6%.d-1) and muscle 0.2-0.6%/d). 7. The FSR in the liver of female diploid was almost 2 times higher than in that of the sterile triploids. 8. The FSR in the muscle, carcass and male gonad were lower in the triploids than in the diploids. 9. Mean whole body protein synthesis (WBPS) in the female and male diploids and in the sterile and male triploids was respectively 4.8, 3.1, 2.0 and 2.3 g/kg.d. 10. The contribution of the muscle to WBPS was greatly lower than that of the liver, the gonad and digestive tract in all the fish studied