A reduced resistance to secondary bacterial infections is often causes by poor biological purification systems, overcrowding, and pollution. These problems are all sources of stress and result in lowering the resistance of the Koi to infections caused by parasites and untreated cuts and bruises. Open wounds allow bacteria and other parasites to enter the body and their enzymes to destroy tissue, providing greater infected areas. These infections can be passed from Koi to Koi.

Preventative maintenence of ponds and early treatment of injuries are the best way to ensure your Koi will not get infected, if they do get infected, the proper medications, whether in food or in the form of injections can help the fish to survive.