AbstractScaling effects on citrate synthase (CS), glucose‐6‐phosphate dehydrogenase (G6‐PDH), RNA. RNA/DNA ratio and protein contents of brain, liver and skeletal muscle were studied in a teleost, Clarias batrachus. The activity of white skeletal muscle CS decreased significantly as a function of increasing body mass of the fish. It shows that the fulfilment of energy demand in white skeletal muscle is not dependent on aerobic metabolism. The activity of liver G6‐PDH decreased with the increasing body mass showing reduction in NADPH generation for lipogenic activity. However, increase in G6‐PDH activity showed enhancement in reductive synthesis in skeletal muscle of the larger‐sized individuals. A positive scaling of RNA, RNA/DNA ratio and protein contents reflects changes in macromolecular turnover for ATP‐supplying enzymes and proteins. J. Exp. Zool. 301A:718–726, 2004. © 2004 Wiley‐Liss, Inc.