Effects of stocking density on growth performance, immune and stress responses in koi carp (Cyprinus carpio var. Koi (Linnaeus, 1758))

The aim of this study was to determine the optimal stocking density in koi carp (Cyprinus carpio var. Koi). For this reason, 2400 juvenile koi (1.28 ± 0.11 g) were stocked at five levels of density (50, 100, 150, 200 and 300 fish per m3) and reared for 11 weeks and growth performance, survival rate, and hematological parameters were evaluated. There was no significant difference between first three treatments, in weight gain, SGR, FCR, mortality and hematological parameters (P>0.05). The minimum weight gain and maximum mortality were observed in treatments 5 and 4, respectively. There was no significant difference between treatments in RBC, WBC, hemoglobin, hematocrit and total protein (P>0.05). The highest amount of immunoglobulin, cortisol, and glucose were observed in treatments 5 and 4, respectively (P<0.05). Levels of lymphocytes were decreased, and levels of neutrophils were increased, by increasing stocking density from 50 to 300 fish/m3. The minimum levels of lymphocytes (73.27±0.12%) were measured in treatment 5. Maximum levels of cortisol (173.97±1.47 ng/ml), was observed in treatment 5 on day 7. According to the results, stocking density more than 150 fish per m3, leading to the growth reduction and incidence of stressful conditions in koi carp, so the optimal stocking density, was 150 fish per m3.