The aim of this article was to present an analysis of different abiotic and biotic factors accounted for abnormal carp (Cyprinus carpio) mortality. The recent developments on diagnostic and etiology of fish viral and bacterial diseases were also reported. Benefits and risks of antibacterial chemotherapeutics and the antiparasitic drugs were presented. It was concluded, that for the effective diseases control, application of sophisticated diagnostic procedures must be combined with experience of fish disease specialists. It was also suggested that chemotherapy is not always necessary to maintain good fish health status, whereas the regular application of certain combination of quicklime (CaO) and table salt (NaCl) appeared to be very effective prophylactic measure against many infectious fish diseases.