Extracorporeal acidic predigestion of commercial dry diets can reduce the incidence of body deformities in the stomachless fish crucian carp (Carassius carassius L.)

The aim of the present study was to test the hypothesis that predigesting commercial dry diets for fish with hydrochloric acid (HCl) can contribute to the reduction of the incidence of body deformities in a stomachless cyprinid species intensively reared under controlled conditions. Two different dry diets (Carpco Crumble by Coppens International and Aller Futura by Aller Aqua), their respective variants modified with HCl, and frozen larval chironomids (control diet) were fed as sole food sources to juvenile Carassius carassius in a recirculating aquaculture system at 25°C for 60 days. At the end of the experiment, visible body deformities occurred exclusively in the groups fed dry diets. The shares of deformities were significantly lower in fish groups fed the modified diets (6.1–13.2%) as compared to those fed the original ones (74.0–87.0%). Fish in the latter groups had significantly the highest condition factor values, which indicated a possible phosphorus deficiency. As evidenced by our results, predigesting commercial dry diets with HCl can be a useful method to mitigate the problem of body deformities occurring in intensively fed cyprinid species.