THE EFFECT OF DIETARY-PROTEIN LEVEL, WATER TEMPERATURE AND GROWTH-HORMONE ADMINISTRATION ON GROWTH AND METABOLISM IN THE COMMON CARP (CYPRINUS-CARPIO)

Two experiments were carried out to study fish growth and several othe r metabolic parameters under three main effects: dietary protein level (40% vs. 21%); water temperature (26 us. 17 degrees C), and intraperi toneal administration of carp growth hormone (cGH) (5 mu g/g body weig ht/week vs. saline). Whereas both higher protein levels and elevated t emperature promoted growth, the effect of cGH administration was highl y dependent on protein level, the largest growth-promoting effect bein g found with low-protein diets. The dependence was particularly signif icant in the first experiment; in which the amount of feed provided wa s highest (5% vs. 2% of body weight/day). At the lower water temperatu re, fish in all treatments showed a significantly elevated hepatosomat ic index. Protein level and cGH administration effects were unclear. T he protein:fat ratio in the body contents was decreased by the high-pr otein diet and lower water temperature, whereas cGH had no effect. In contrast, the glycogen:fat ratio depended mainly on temperature-yieldi ng higher ratios at the lower temperature, and not on cGH or protein l evels. Carp GH administration decreased AcCoA carboxylase activity in the liver. Water temperature did not change the level of GH or T-3 in the plasma. Protein level did not influence GH but increased T-3, wher eas GH expression in the pituitary gland was downregulated by the admi nistration of cGH and by the low-protein diet.