The development and mass triggering of the ilnesses in fish, which may lead to considerable mortalities may take place mainly during and after the wintering of the fish, being well known the fact that the wintering period is one of the most critical ones in their life.
Thus, in conditions consisting of low temperature water, reduction of the intensity of the metabolical processes, secession of feeding and seeing to the energetic needs of the fish based on the acumulated reserves, the setting for wintering under weigth and in unhygenic tanks, unfit for this faze, is vulnerable to attack from pathogenic agents.
Due to the fact that lately there have been recorded losses by mortality in fish populations in the period imediately after wintering, the investigation of the health state of the fish right after taking it out of wintering for the purpose of organising measures of preventing and combating of ilnesses.
So, during the period of 2003-2004, researches regarding the health conditions after wintering of the main species of cultured fish at the Brates farm have been done. On this farm some losses of the fish material both during wintering and in the next period have been recorded. | 
