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Abstract Fish like the other ectothennic (poikilothennic) animals are unable to regulate their body temperature. Fish body temperature varies with the environmental temperature which afTect a variety of physiological and biochemical processes. The& acclimation at different temperature degrees results in a wide variety of metabolic changes in fish. The activities of twelve metabolic enzymes were assayed in an attempt to through some light on intermediary metabolism of fingerlings of the Nile tilapia (Oreochromis niloficus). The enzymes selected are representative in different metabolic functions and cell compartmentation in white muscle and liver. The nature of changes in the activity of key enzymes operative in 1) ,. glycolysis, Krebs cycle, malate shuttle (hydrogen shuttling redox regulation in cytosole and mitochondria), amino acid metabolism in white muscle and liver, 2) malate pyruvate cycle in white muscle) 3) gluconeogensis in liver. The selected key enzymes are: hexokinase (HK, EC 2.7.1.I) , phosphofmctokinase (PFK, EC 2 7 1 1 1, pyruvate kinase (PK, EC. 2.7.1.40) and lactate dehydmgenase (LDH, EC 1.1.1.27) ”glycolysis ”; NADP-isocitrate dehydrogenase (NADP-IDH, EC 1.1.1.42) and succinate dehydrogenase (SDH, EC 1.3.99.1). |