Use of body-water content to assess the physiological state of roach Rutilus rutilus L. in natural conditions

It is shown that in natural conditions roach have two levels of water content in their organisms during their annual cycle which reflect different physiological states of the fish. During the feeding period, the body-water content is maintained at a low level of 72.6 +/- 0.05%, determining the physiological state related to the growth of fishes. In winter, spring, and postspawning periods, the water content in the roach organism is high, 75 +/- 0.06%, which reflects the physiological state of survival during periods of the year unfavorable for growth. The water content in the organism of fish is a convenient integrated parameter for assessing the general physiological state of fish in natural conditions.