عنوان مقاله [English]
نویسندگان [English]چکیده [English]
In the present study, growth indices, body composition and digestive enzymes of juvenile common carp (Cyprinus carpio) were investigated in biofloc system with different stocking rates. So, 825 juvenile fish (17±1.2g) were randomly transferred to 15 fiberglass 200 liter tanks in lab of Khorramshahr University of Marine Science and Technology. Twenty five fish were stocked in a tank (2.12 kg/m3) with water exchange (control), and also 25 (2.12 kg/m3, D25), 50 (4.24 kg/m3, D50), 75 (6.37 kg/m3, D75) and 100 fish (8.5 kg/m3, D100) were stocked in tanks as a biofloc treatments. The photoperiod included 12 h light and 12 h darkness and the duration of the experiment was 40 days. Control and other treatments treatment were fed with a commercial diet containing 35% and 25% protein, respectively for 40 days. The fish were fed manually, three times a day (8:30, 12:00 and 15:30) based on 3% of the body weight. In the control treatment, the water was exchanged 25% every two days. Dissolve oxygen, temperature, pH and salinity parameters were not significantly different in biofloc system compared to the control (P>0.05). Biofloc volume (BF) and total suspended solids (TSS) values were higher in biofloc treatments than the control (P<0.05). Total ammonia and nitrite levels were lower in biofloc treatments than the control (P<0.05). The nitrate levels were higher in D100 treatment than other biofloc treatments (P<0.05). Final weight, percentage of weight gain, specific growth rate and feed conversion ratio were not significantly different in D25 and D50 treatments compared to the control (P<0.05). The protein efficiency was significantly increased in B25 and D50 treatments compared to the control (P<0.05). The lowest protein content was observed in D100 treatment compared to the other treatments (P<0.05). The lipase, amylase and alkaline phosphatase activities did not show significant difference in biofloc treatments compared to the control (P<0.05). The results of this study showed that biofloc system decreased the consumption of dietary protein while reducing the pollution load of nitrite and total ammonia.