The experiment was run on carp individuals (384 ± 5g) kept in cages in heated water. The fish were randomly divided into two groups fed two different isoprotein diets, one with increased carbohydrate level (33.3% of the dietary energy; Group I) and the other with increased fat level (39.3% of the dietary energy; Group II). The experiment resulted in statistically significant differences in the contents of selected biochemical blood components as well as in the body composition of carp and culture efficiency indices in relation to the pre-experiment values and between the groups. In view of the 100% survival rate and high body weight increments, it is concluded that the diets used in the experiment, although differing in their carbohydrate and fat contents, and in spite of exerting significantly different effects on fish organism, were compatible with the fish physiological adaptive potential for their utilisation. It can be then presumed that diet-dependent modification of fish body composition to obtain certain levels and composition of lipids can play one of major roles in the intensive fish culture in the future.

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