The aim of present study was to determine the effects of biofloc systems with different carbon sources and carbon to nitrogen ratio on growth performance, intestinal morphology, nonspecific immune response and the possibility of reducing feeding ratio of Nile tilapia (Oreochromis niloticus) in biofloc system in fresh and brackish water. The experiment consisted of three stages of biofloc production, fish rearing in the biofloc system, and reduce the feeding ratio in the biofloc system. The first two experiments designed separately in fresh and brackish water in 5× 2 factorial design at 5 different levels: two carbon sources as the first variable (including 100% molasses (A), 75% molasses + 25% wheat flour (B), 50% Molasses + 50% wheat flour (C), 25% molasses + 75% wheat flour (D) and 100% wheat flour (E) and two carbon to nitrogen ratios (15:1 and 20:1) as the second variable, with three replicates. Overall, the experiment included 10 biofloc treatments in fresh water and 10 biofloc treatments in brackish water. In addition, in the second phase of the experiment, a clean fresh water system was used as a control test. The first experiment was performed over a 42-day period and the second experiment over an 8-week period. The results showed an improvement in growth performance, humoral immune response and an increase in length and diameter of intestinal villi of fish raised in biofloc systems in both freshwater and brackish water by increasing wheat flour composition as an organic carbon sources at a carbon to nitrogen ratio of 15:1. Significant weekly changes were observed in TAN, NO2 and NO3 levels (P <0.05). In both, fresh and brackish water culture systems, among different experimental groups, fish in biofloc systems with 100% wheat flour and carbon to nitrogen ratio of 15:1, showed the highest growth performance by improving intestinal histopathological performance and immune response. In the third experiment, experimental fish were fed at 40, 60, 80 and 100% of daily ration at the presence of biofloc and one the control group received 100% original diet over a 56-day period. The results of the growth performance of fish raised in freshwater showed that fish fed with 80 to 100% commercial feed in biofloc system, have a significantly higher weight, specific growth rate and daily growth rate than other experimental groups. (P <0.05). In brackish water treatments, the highest increase in body weight, specific growth rate and daily growth rate percentage was observed in fish fed with 100% commercial food in biofloc system (P <0.05). The results of hematological parameters of Nile tilapia reared in biofloc system showed that after 8 weeks, the number of white blood cells, red blood cell count, hemoglobin, hematocrit and liver enzymes of fish cultured under different treatments were not significantly different from control group (P >0.05). Finally, according to the results obtained in the third experiment, it can be concluded that in the freshwater biofloc system, the amount of feeding can be reduced by 20 to 40% daily ration without any negative effects on fish growth performance and health. Also, in the biofloc system of brackish water, a 20% reduction daily feeding showed no negative effect on fish growth performance and health. In general, based on the results, it can be concluded that the use of biofloc technology in culturing of Nile tilapia has beneficial effects on maintaining water quality, improving food consumption and growth performance, increasing the protein content of fish, improving immune responses and increasing absorption capacity of intestine.

عيسي ابراهيمي درچه

اميرحسين جلالي- جولي اكاساري

غلامرضا رفيعي، اميدوار فرهاديان، نصراله محبوبي صوفياني