Integrative approach of histopathology and histomorphometry of common carp (Cyprinus carpio L.) organs as a marker of general fish health state in pond culture AbstractThe semi-intensive system of common carp monoculture in earthen ponds is currently the most practiced fish rearing system in several countries in Eastern Europe. This system is based on the addition of supplemented feed to ponds to achieve faster growth. In this study, the general state of the fish health was monitored when three different types of feeds were used: grain cereals (CF), commercial pelleted feed and extruded feed. The markers used were: (i) the histopathological index (HP) of the main organs: gills, liver and kidney; and (ii) the histomorphometric parameters of the hepatocytes and enterocytes to assess the state of the digestive system in fish fed different types of supplemented feed. At the end of the experiment, the fish were in good health, since irreversible lesions were not noticed to a greater extent in any of the fish organs. There were also no other severe lesions present. However, the results showed differences in the HP indices of the liver and gills, as well as the total HP index, indicating a better health status of the fish in the CF group. The histomorphometric results showed larger cytoplasmic areas of hepatocytes in fish fed CF, which is attributed to glycogen accumulation and higher numbers of goblet cells in the distal intestines of fish fed compound feeds. This can be attributed to slight inflammation.

A four‐and‐a‐half months study was conducted in nine earthen ponds to evaluate the addition of different supplemental feeds as a management tool for enhancing natural food availability and common carp growth, while maintaining optimal water quality in the semi‐intensive system. Three supplemental feeds were used: commercial extruded and pelleted feed with 25% protein and 7% fat and cereals. The type of supplemental feed did not influence water quality, except hardness, but significantly affected abundance of cyanobacteria, natural food availability and common carp growth. The use of pelleted feed was related to the lowest abundance of cyanobacteria in the ponds. For the two groups of large zooplankton, Cladocera and Copepoda, abundances were higher in the ponds with pelleted feed compared with the ponds where cereals and extruded feed were used. The abundance of benthic macroinvertebrates in the treatment with pelleted feed was three times higher than in the other two treatments. The results of this study indicate that pelleted feed can help farmers not only as a source of nutrients for carp growth but also indirectly as a management tool for maintaining ecological stability and control of cyanobacterial bloom in ponds.