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A 12-week feeding trial with common carp (Cyprinus carpio) was conducted to test the hypothesis that compound diets formulated on the basis of different soybean cultivars will have effects on growth parameters, feed utilization, and digestive system histology. Soybean grains were from the following cultivars: Alisa (SB-A), Balkan (SB-B), and Galeb (SB-G). The fourth tested diet contained grains from a mixture of different SB cultivars (SB-M). The results confirmed the tested hypothesis, as the fish from the group SB-A showed higher average weight gain, specific growth rates, and feed efficiency, as well as lower feed intake and feed conversion ratio, compared to the groups SB-B and SB-M. On the other hand, diets were expected to cause inflammation in the distal intestine of the fish, but this did not occur. Histological examination of the intestine and liver, performed at the end of weeks 1, 3, 6 and 12, showed no pathological changes. Most of the differences between the groups were found at the end of the trial. The group SB-A had a higher surface area of different intestinal layers compared to the groups SB-B and SB-G. The surface area of the goblet cells was greatest at most of the time points in SB-M. In the liver, the evaluation of the surface area of hepatocytes and their nuclei showed no significant differences between the groups. The differences in final body mass, which showed a maximum value of 18% between the groups, could be of significant importance for culture of this freshwater species. [ABSTRACT FROM AUTHOR]

In the last 60 years, pond farming of common carp (Cyprinus carpio) in Europe has gradually intensified, which has increased the stocking density and amount of supplementary feed, resulting in higher yields. Additionally, compound feed has been introduced to semi-intensive farming to increase the growth of farmed fish. Feed quality affects growth directly through conversion efficiency and indirectly by influencing fish physiology. In the present study, juvenile common carp were grown in net cages in a fishpond for 80 days and fed the same amount of different supplementary feed: wheat, pelleted, or extruded feeds or fish relied only on the available natural food (control group). Growth, microanatomy of the liver and distal intestine, and morphology of erythrocytes were evaluated. Compound feed had beneficial effects on the growth and histological parameters compared to the control group and fish fed wheat. This included higher surface areas of erythrocytes and hepatocytes' nuclei, longer intestinal folds, and thicker tunica muscularis in the distal intestine. The study showed that increased growth and use of compound feeds did not cause any physiological trade-offs that would be depicted in quantitative histomorphometry, and there was an absence of histopathological changes. [ABSTRACT FROM AUTHOR]