Effects of feeding commercial diets on the development of juvenile crucian carp Carassius carassius: digestive tract abnormalities

Wild-living populations of the crucian carp Carassius carassius, a cyprinid fish of European freshwaters, have decreased in recent years, likely due to increasing competition presented by invasive species. Several initiatives have been launched in an attempt to reintroduce this fish back into its natural habitat, but these approaches require the use of crucian carp fry reared under controlled conditions, and the use of popular and inexpensive commercial diets has been found to result in developmental abnormalities. The aim of the current study was to analyse the impact of feeding juvenile crucian carp either natural food (Chironomidae sp. larvae) or 2 commercial diets, with a focus on the intestinal development of these fish. Histological analysis revealed significant pathologies in the alimentary tracts of fish fed both commercial diets; these included lowered hepatocyte and enterocyte proliferation, as well as shortened intestinal folds. Furthermore, the digestive enzyme activity patterns suggested a physiological state close to malnutrition. This study confirmed that basic commercial diets (at least the 2 applied) are not recommended for the rearing of crucian carp juveniles, even though initial growth rates of the fish might suggest otherwise.