Histopathological indicators: a useful fish health monitoring tool in common carp (Cyprinus carpio Linnaeus, 1758) culture

In order to evaluate the relationship between water quality in ponds and indices of histopathological changes occurring in the vital organs of the common carp (Cyprinus carpio L., 1758), two six-month field experiments were carried out using two different water supplies: from the nearby stream and a tube well. The fish were fed supplemental feed: raw cereals, pelleted and extruded compound feed. Histopathological analysis, alteration frequencies, and semi-quantitative scoring of the changes were used to assess the health status of the fish. Ponds supplied by stream water were characterized by higher water hardness, dissolved oxygen and pH values, while those supplied by the tube well had higher electroconductivity, total ammonium and orthophosphates content. Fish survival rate and habitat suitability index were lower in ponds supplied by stream water, while the weight gain did not differ between the two water supplies. The use of stream water resulted in a higher level of histopathological changes in gills and liver. Among the water quality parameters, pH level had the strongest influence on fish. Differences in water supply produced greater influence on the level of histopathological changes than the type of feed applied. Gills were the most sensitive organ, while the kidney was the least responsive.