Risk factors for a population of perch Perca fluviatilis (Lake Arahley, Zabaikalskiy krai)

The structure of ichthyocoenoses is defined not only by the influence of natural factors, submitting to regional and local regularities, but also by variety of anthropogenic influence. Control fish crops on lake Arahley, lead in 1998- 2008, have confirmed its structure as perch reservoir and have revealed gradual decrease in relative density of the perch. Risk factors for population of the perch in lake Arahley during 2008-2009 years are the combination of ad-verse climatic parameters and the maximal biomass of the perch for last 20 years was. Intense ecological conditions was reflected in immune system of fish communities that has led to magnification of susceptibility of fishes to vari-ous infections, and presence potentially pathogenic microorganisms has provoked their disease. In march 2009 in lake Arahley it was noted the flash of aeromonosis. The perch who makes a basis of trade and sport fishery is subject to disease. During the autumn-winter period of 2009-2010 year the morbidity of the perch was 90%. One of ways of the decision of given problem is complex and regular monitoring the lakes condition, based on modern methods and approaches which will allow to reveal early stages of mass development of illness activators of fishes.