Protein turnover in temperate and tropical fish
The rate of protein growth, synthesis, RNA/protein ratios, RNA activity and protein content in the whole body and specific tissue of five economically important fish species were investigated under a variety of conditions known to affect both the growth and synthesis rate. Theses species were goldfish, tilapia and 3 different species of flatfish plaice, turbot and flounder. In goldfish, water temperature had an effect on both the growth rate and synthesis rate. Cold- acclimated goldfish exhibited higher RNA/protein ratios compared to warm-acclimated goldfish. The warm-acclimated goldfish had higher RNA activity when compared with the cold- acclimated goldfish. In goldfish and tilapia the linearity between ration and growth rate is a reflection of linearity between protein synthesis and protein deposition. In tilapia and plaice the rates of growth, synthesis and degradation declined with increased in the body size. In tilapia, scaling relationships for growth, protein synthesis, protein degradation, RNA/protein ratio and RNA activity were determined. The highest rate of growth and synthesis were observed in the smallest fish. Efficiencies of retention of synthesised protein were calculated; the higher growth rate of tilapia compared with goldfish at similar rations is due to the high efficiency of retention of synthesised protein of this species. Flatfish at low temperatures exhibited lower protein growth rate, higher protein synthesis, degradation and higher RNA/protein ratios as compared to the higher temperatures groups. Efficiency of protein retention in the flatfish increased at higher temperature. The effect of ovine growth hormone and heavy metals on flounder were investigated. After 13 days exposure, growth rates of the growth hormone-injected animals were stimulated by more than 8-fold compared with controls. Increased growth rates were brought about by increased fractional rates of protein synthesis in the whole bodies with little change in protein degradation. Tissues response were similar to whole body results. The increased rates of protein synthesis were brought about with little change in RNA concentration in the tissue; hence RNA translation efficiency had been increased by the growth hormone. Flounder exposed to heavy metals with growth hormone did not exhibit the same stimulation in growth rate compared with growth hormone alone, growth rates stimulated and protein synthesis rates were elevated.