The effects of rearing Pacific white-leg shrimp (Litopenaeus vannamei Boone, 1931) in biofloc system on the immune responses and survival rate in challenge with Vibrio harveyi

Shrimp culture, one of the most profitable industries, needs to be modified by modern techniques in Iran. The present study was focused on the effects of applied biofloc technology (BFT) on Pacific white-leg shrimp (Litopenaeus vannamei) culture, as a new system (zero-water exchange) to improve the immunity of shrimp and the water-quality factors in challenge with Vibrio harveyi. Biofloc systems were established by increasing the carbon/nitrogen (C/N) ratio by adding sugar as a carbohydrate source to the culture media. The immune system indices, and growth factors of shrimp were then measured along with water quality parameters and loads of Vibrio harveyi compared to the traditional water-exchange system. The results showed that using BFT led to decreasing levels of the toxic nitrogenous substances such as TAN, NO3, and NO2, which in turn resulted in decreasing the water exchange frequency. It was also observed that the shrimp could feed on flocs resulted in improvement the growth factor and immune system. On the other hand, despite the increased loads of V. harveyi bacteria, there was no significant difference in shrimp survival between the biofloc and traditional systems. These observations were confirmed by evaluating immune system factors (total hemocyte count (THC), total plasma protein and phagocytosis activity of the hemocytes. Generally, this study showed that rearing pacific white-leg shrimp in BFT in can preserve water quality and enhance shrimp's growth and immune responses, compared to the traditional systems.