The effects of exhaustive swimming on a number of metabolic parameters were assessed in six organs of rainbow trout (Oncorhynchus mykiss). Glycogen phosphorylase was activated in four organs (liver, gill, heart, and white skeletal muscle), the largest increases in phosphorylase a activity being 5.3‐ and 6‐fold in liver and white muscle, respectively. Exhausted fish showed elevated lactate levels in all organs except brain with absolute increases of about 12 μmol/g wet weight in white and red skeletal muscles but only about 1 μmol/g in internal organs. ATP content dropped dramatically in skeletal muscles after exercise but remained constant in other organs. Fructose‐2,6‐bisphosphate levels rose in liver and brain but dropped in gill and heart during exercise. Kinetic properties of trout liver 6‐phosphofructo‐1‐kinase and pyruvate kinase were assessed in control versus exhausted fish. Neither enzyme showed changes in substrate affinities, ion cofactor affinities, or sensitivities to metabolite inhibitors or activators as a result of exercise, giving evidence that these liver enzymes (unlike glycogen phosphorylase) were not modified by reversible protein phosphorylation in response to muscle exercise. Exhaustive exercise also resulted in major changes in the levels of various free amino acids in trout organs. Alanine content rose by 9–11 μmol/g in heart, gill, and brain. Glycine increased by 12 μmol/g in white muscle and by 0.4–2 μmol/g in liver, heart, and gill. Several organs also showed significant changes in glutamate and glutamine contents and free histidine content increased in others, most notably by 2.8 μmol/g in white muscle. Organ‐specific patterns of response to the exercise stress are indicated. Copyright