The effect of thyroid hormones an growth and metabolism of two species of teleost fish
Both short term and long term effects of thyroid hormones on growth and protein metabolism were studied in tilapia and carp. The hormones were either fed or injected intraperitoneally. Only T3 was able to induce growth in tilapia. No effect on carp growth was observed. Certain biochemical changes were also recorded in liver, muscle and brain of tilapia fed these hormones. After a latent period of 12 -48 hours a single injection of both T4 and T3 induced increases in protein and RNA in liver and muscle of tilapia and carp. Actinomycin D inhibited this response to a certain extent. Thyroid hormones seem to be more important in the early than in later life of the tilapia as far as the growth is concerned. Temperature mediates the effects of T4 and T3 on cellular level but seems to be ineffective in blocking the distribution of the labelled T4 to subcellular organellae. The effects of temperature in turn seem to be dependent upon the nutritional status of the fish.
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