INTERRELATIONSHIPS BETWEEN STOCK DENSITY AND CONDITION DETERMINANTS IN TENCH (TINCA-TINCA L.) FRY IN POLYCULTURES WITH HERBIVOROUS FISH

The production results achieved in experimental pond polycultures of y oung tench (Tinca tinca) with silver carp (Hypophthalmichthys molitrix ) or grass carp (Ctenopharyngodon idella) were processed. The regressi on analysis was used to find out how fish density expressed in differe nt final survival rates at the end of the growing season affects tench weight and condition determinants. Tench were significantly negativel y affected in condition as expressed by Fulton's (P < 0.05) and Clark' s (P < 0.01) coefficients and in total protein content in blood plasma (P < 0.05). Hematocrit value and final individual weight decreased wi th increasing stock density but the effect was not significant. Determ inants of biochemical composition (dry matter, ash, fat and crude prot ein contents) were not affected. No significant relationships (except for the dry matter in grass carp flesh) between these parameters were found in the two species of herbivorous fish tested.