Microcystins appear to be considered one of the most dangerous cyanobacterial toxins in the world. The accumulation and change of microcystins MC-LR and MC-RR in the “cyanobacteria–cladocera–fish” food chain were studied. Microcystis aeruginosa was fed to Moina macrocopa at three densities, 5.0 × 10³, 5.0 × 10⁵, and 5.0 × 10⁶ cells/mL, and then passed to Cyprinus flammans. The total amount of MCs in the cyanobacteria cell extract increased with increasing density. The content of MCs in M. macrocopa increased with the feeding density of M. aeruginosa. In the final stage of experiments, MC-RR was the only MC that could be transmitted by M. macrocopa and persisted in red carp. In this study, changes in the concentrations of MC-LR and MC-RR in the liver of red carp seem to indicate some kind of transformation or degradation mechanism. It shows the possibility of MCs concentration-controlled biodefense in eutrophic waters.

Carp of the initial individual weight about 1 kg were fed in cages with four kinds of extruded feeds differing in the lipid content (7.5-19.5 percentage). The main source of lipids was a poultry fat. The most favourable results of rearing were achieved while feed containing 15.3 percentage of lipids was used in carp feeding

The effects of two benthivorous fishes, common carp (Cyprinus carpio) and calbasu (Labeo calbasu), on bottom soil resuspension, water quality, nutrient accumulations, fish diet and growth of rohu (Labeo rohita) were compared. In this study, individual tanks receiving bottom soil and water from a central pond were used to more naturally simulate rohu polyculture pond conditions. Two treatment combinations were performed in triplicate for 4 weeks: 6 rohu plus 3 common carp per tank and 6 rohu plus 3 calbasu per tank. Resuspension of bottom soil, free CO₂, and nitrogen and phosphorous concentrations in the water column were greater in the tanks with common carp while dissolved oxygen, pH, and total alkalinity were lower. Common carp increased the % nitrogen and % phosphorous accumulation in plankton and fish, while these nutrients were reduced in benthic macroinvertebrates and bottom soil. Gut contents of harvested calbasu contained a combination of benthic macroinvertebrates and zooplankton, rohu contained phytoplankton and zooplankton, and common carp contained almost entirely (82%) macroinvertebrates. Rohu shifted from zooplankton to phytoplankton when competition for zooplankton was higher in calbasu tanks. Since common carp preferred benthic macroinvertebrates they overlapped little with rohu for food. Common carp increased the harvesting weight and growth rate of rohu and thus had greater potential than calbasu to increase yields for rohu polyculture farmers.