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Biofloc technology has mentioned as a new tool for sustainable aquaculture development and has overcome the problems of water scarcity and discharge of aquaculture effluents to the environment. In this system, nitrogenous wastes (Ammonia and Ammonium) are simultaneously recovered by bacteria and converted into microbial proteins that can be consumed by aquatic animals. The purpose of this study was to investigate the factors affecting the production of biofloc and evaluate it for use in aquaculture. The effect of different temperature levels (24, 28, 32 °C), salinity (0, 4, 8 g/l)  ,and C/N ratio (10:1, 15:1, 20:1) which are the main key factors to the formation and function of biofloc system was evaluated by using a response surface method designing. Moreover, the influence of those factors on total ammonia nitrogen, nitrite, nitrate, floc volume, protein, and lipid content of biofloc was investigated. The results showed that the temperature had a significant effect on floc volume and protein content of biofloc (P < 0.05), but it had no significant effect on other nitrogenous compounds and lipid content (p > 0.05). The protein, lipid and moisture of biofloc particles were decreased by increasing salinity significantly (P < 0.05). Also, TAN and nitrite concentration influenced by C/N ratio inversely. According to the factors Optimization, providing 27 °C and C/N ratio of 18:1 in brackish water and 29 °C and C/N ratio of 14:1 in fresh water resulted in high quality biofloc production and control of nitrogenous wastes in water.

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The aim of this study was to evaluate the effects of feed supplemented with different levels of Selenium Nanoparticles (SeN) on growth, survival, and biochemical indices of Acanthopagrus latus. Yellow-tail seabream fish with a mean weight of 52±3 gwasfed with four experimental diets containing 0, 0.5, 1, and 2 mg kg^-1 SeN for 8 weeks. At the end of the experiment, the fish fed 0.5 mg kg^-1 SeN showed a significant improvement of weight gain compared to the control (P< 0.05). Specific growth rate, feed conversion ratio, and survival were not significantly different between treatments (P> 0.05). The lowest activity of alkaline phosphatase, alanine amino transferase, creatinine phosphokinase and cholesterol were observed in 0.5 mg kg^-1 SeN treatment, which was significantly lower than the control (P< 0.05). Although aspartate amino transferase, lactate dehydrogenase, triglyceride and creatinine were not significantly different among experimental treatments (P> 0.05), total protein and albumin levels were significantly increased in the 1 and 2 mg kg^-1 SeN treatments compared to the control group. The highest level of globulin was observed in the 2 mg kg^-1 SeN treatment. According to the results, the addition of 0.5 mg kg^-1 SeN to fish feed could improve growth and biochemical parameters.