Impacts of water additives on water quality, production efficiency, intestinal morphology, gut microbiota, and immunological responses of Nile tilapia fingerlings under a zero-water-exchange system

Abstract

The impacts of commercial probiotics as water additives to the zero-water exchange system on water quality, production efficiency, gut microbiota, antioxidant, and immunological responses of Nile tilapia (Oreochromis niloticus) were investigated. Five treatments, with three triplicates, were randomly designed, where in each replicate 150 fish (100 ± 4.5 g) were stocked in 20-m3 concrete ponds. Different water probiotics were added to ponds' water as follows: T1 (Control: no probiotic added); T2 (Prozym powder Ultra ® at 0.002 g/ m3/ day); T3 (Microban aqua ® at dose 0.002 g/ m3/ day); T4 (Aquastar ® at dose 0.0015 g/ m3/ day); and T5 (Sanolife PRO-W ® at dose 0.0010 g/ m3/ day). For eight weeks, fish in each group were fed a commercial feed (30% crude protein) up to satiety three times a day. After the experimental period, dissolved oxygen in ponds' water was significantly improved, while ammonia, nitrite, and nitrate levels were significantly lowered by water additives as compared to the control group. Compared to the control group, yield, specific growth rate, and total feed intake were significantly improved, while feed conversion ratio was not significantly changed among different treatments. Significant (p < 0.05) increases in villus height/width, and the absorption area was observed in groups that received water additives. Total Vibrio spp. counts in fish guts and ponds' water were significantly lower, while the total Bacillus spp. counts in both ponds' water and fish guts were significantly higher in probiotic-treated groups. Hematological parameters (counts of white blood cells and red blood cells as well as hemoglobin and hematocrit levels) significantly (p < 0.05) increased in probiotic-treated groups. In similar trends, antioxidant (superoxide dismutase and catalase activities) and immunity (total protein, globulin, immunoglobulin, and lysozyme activity as well as activities and index of phagocytes) were significantly enhanced in the groups treated with water probiotics. Overall, our results show that water probiotics in the current study were beneficial for reducing the nitrogenous compunds in ponds'water and improving the production efficiency, gut microbiota, antioxidant and immunological responses of Nile tilapia.