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S-metolachlor is one of the most frequently used herbicides worldwide. However, toxicity studies of this herbicide to aquatic organisms are scarce. In the present study, two experiments were conducted to test the effects of S-metolachlor on common carp, one of the most economically important fish species, with a distribution throughout the world: (1) 96 h acute semi-static toxicity test, aiming to determine LC50; (2) a subchronic semi-static test that lasted 28 days, in which juvenile carp were exposed to 3%, 8%, and 25% of previously determined LC50—0.5 mg·L−1, 1.4 mg·L−1, and 4.1 mg·L−1, respectively. Several biomarkers were employed to assess fish responses to toxicants. Blood biochemistry analysis and nuclear alterations of erythrocytes did not show any difference among experimental groups. Semi-quantitative histopathological analysis revealed mild alterations in the gills and liver, where oedema of secondary epithelium of gills and leukocyte infiltration in liver were significantly higher in fish exposed to 1.4 mg·L−1 and 4.1 mg·L−1. Histopathological indices in liver, as well as the total histopathological index, also showed significantly higher scores in the same groups. Bioconcentration factors of S-metolachlor ranged from 3.2 to 9.4, depending on the experimental group. [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]