Carp, Cyprinus carpio, were subjected to a short term of fasting (2 months) and 12 days of refeeding. The early changes produced in plasma metabolites and hormones (insulin and glucagon) and their respective energy contribution in liver and muscle during fasting and refeeding was studied. Two phases of fasting were differentiated. The first phase (until day 8 of fasting) was characterized by a reduction in the hepatosomatic index mainly due to glycogen mobilization. A transitory increase in plasma glucose and lactate suggested an initial increase in energy demand. No changes were produced in the percentage of glycogen and protein in muscle, but musculosomatic index and the total body muscle protein decreased. Although the most depleted tissue in this phase was the liver, the loss of energy content of total muscle was higher. Stabilization of liver glycogen content, plasma glucose and lactate levels, decreased muscle protein levels and a reduction in the rate of body weight loss characterized the second phase (from day 8 of fasting). Protein content in whole muscle decreased by 22%, similar to the first phase. The energy expenditure of both liver and muscle was lower in this phase. Plasma insulin levels decreased two-fold and plasma glucagon three-fold in the first phase and remained low in the second phase of fasting. Twelve days of refeeding produced a greater increase in daily growth rate than in the control group and a recovery of plasma insulin, glucagon and glucose levels. Liver completely recovered. In contrast, musculosomatic index, protein and lipid content indicated that muscle did not completely recover from the 2 months of fasting, although and overshoot of muscle glycogen was observed.