Effect of Stocking Density on Leuckocyte Reaction of Oncorhynchus mykiss (Walbaum, 1792)

This study evaluates the hematological response of rainbow trout fingerlings to crowding stress induced by high stocking densities, during a 33 days period. A number of 254 rainbow trout, with an average weight of 29.51 ± 1.32 g, were divided into four rearing units in order to create different stocking densities: in DS1-2.64 kg/m3, DS2-5.16 kg/m3, DS3-7.12 kg/m3 and in DS4-9.42 kg/m3. To determine the leukograma and also the absolute number of leukocytes, blood samples were collected after the experimental trial and used immediately to make smears. Physiological stress induced by maintenance under different stocking densities is reflected by rainbow trout leukograma. We can notice a decrease of absolute number of leukocytes, with direct implication of stocking density level, from 69.79±10.22 (x103cel./mm3) in DS1 to 46.34±9.83(x103cel./mm3) in DS4. In this experiment, the immune (defense) system has been influenced by stocking density, the general reduction of leukocytes number being a characteristic response to stressful conditions.