Background. Constant improvement of animal feed formulas calls for new raw materials. In the feeding of fish, one of diet recipe optimization methods is to search for feed protein sources alternative to fish meal. The presently reported study focuses on an unconventional protein source—the erythrocyte meal—for feeding fry of common carp. Materials and methods. The barothermal method (extrusion) was applied for the formulation of experimental feeds prepared as isonitrogenous and isocaloric diets. In the feeds tested, the erythrocyte meal was used as fish meal substitutes at different substitution levels (control diet C = 0%, E5 diet = 5%, E10 diet = 10%, and E15 diet = 15%). The feeds were evaluated on the basis of their physical and chemical characteristics. The feeding trial was carried out on the fry of carp (3.8 ± 0.1 g). The experiments were carried out under controlled conditions in an indoor fish tank facility in twelve 60-L flow-through aquaria. Each aquarium was stocked with 14 fish. In the final evaluation of the feeding tests, the following rearing effectiveness indices were used: food conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), and survival rate (SR). The data obtained were statistically processed using Statistica computer software. Results. At the end of the experiment, the fish body weight from treatment C was significantly (P < 0.05) higher than the weights of treatments E5 and E15. Significant body weight differences occurred also between treatments E5 and E15. Values of specific growth rate (SGR) depended on the type of applied feed. The minimal value (1.86% • d-1) was reached in treatment E15, while the maximal value (3.34% • d-1) was recorded in treatment C. The most favourable FCR and PER values were recorded for C feed and they differed significantly from the values obtained with other experimental feeds. The application of experimental feeds to carp resulted in an increase in dry matter content in all treatments, and total protein and fat in the fish bodies from groups C and E5. However, there was no change in body ash content at feeding trial. Conclusion. Experimental results showed that the erythrocyte meal addition at 5%, 10%, and 15% rate as replacement for 15% of fish meal did not improve the rearing parameters of common carp fry.

feeding, erythrocyte meal, fish meal substitution, diets, carp, Cyprinus carpio