Optimizing Stocking Density in Biofloc Culture of Juvenile Common Carp (Cyprinus carpio) Using Growth and Immune-biochemical Indices as Indicators

The optimizing stocking density for biofloc technology is essential for improving fish growth and profitability of aquaculture. The treatments consisted of different stocking density of 125, 250, 375, and 500 common carp (Cyprinus carpio) fish/m3. Fish with an initial average weight of 17.10±0.3 g were fed three times per day in triplicates for 40 days with a commercial diet (25% crude protein), and the ratio of carbon to nitrogen 20 in each treatment. The water nitrogen substances enhanced by increased stocking density (P<0.05). The final growth (-19.75%), whole-body protein (-2.84%), lipid content (-7.27%) significantly decreased, and food conversion ratio (+67.29%) increased in the treatment of 500 fish/m3 compared to the treatment of 250 fish/m3 (P<0.05). Serum glucose (-11.09%), triglycerides (-11.24%), high-density lipoprotein (-26.16%), and low-density lipoprotein (-31.98%) levels significantly reduced, but serum cortisol concentrations (+13.08%) and, liver enzymes increased in the treatment of 500 fish/m3 compared to the treatment of 250 fish/m3 (P<0.05). Total protein (-9.01%), globulin (-12.80%), ACH50 (-4.97%), and lysozyme activity (-9.21%) significantly reduced in the treatment of 500 fish/m3 compared to the treatment of 250 fish/m3 (P<0.05). The best performance of fish was observed at stocking density up to 250 fish/m3 in the biofloc system.