Cultivo da tilápia do nilo (Oreochromis niloticus) em diferentes salinidades utilizando sistema de biofloco

Abstract

Aquaculture water reuse system com be applied to saline tolerant species as an alternative for brackish water ponds. Therefore, the aim of this study was to evaluate the influence of salinity on the variables of water quality, the performance and welfare indicators on Nile tilapia (Oreochromis niloticus) culture with biofloc system. Five treatments were performed involving the salinities of 0, 4, 8, 12 and 16 g/L with three replicates. The fishes were stoked in fiberglass tanks (800L) and cultured for 90 days at a density of 30 fishes/m3 and average initial weight of 93,8 g. Molasses was used as a organic carbon source for controlling the total ammonia nitrogen levels (NAT) and induce the development of heterotrophic bacteria during the production cycle. During the study were evaluate variables of the water quality, performance ratios and hematological indicators, related to welfare of fishes. The temperature, chlorophyll-a, settleable solids and total suspended solids showed no statistical difference between salinities (p≥0,05). The average levels of NAT (3.94 mg/L) and nitrite nitrogen (0.82 mg/L) were lower in salinity 0 g/L. As the zootechnical performance, the final weight ranged 256-280 g with feed conversion rate between 1.4 and 1.6. The daily weight gain did not differ between salinity 0, 4 and 16 g/L (2.1, 1.9 and 1.9 g/day, respectively) (p≥0,05). Highest yields were obtained in salinities 0 (8.4 Kg/m3) and 16 g/L (8.0 Kg/m3) and the salinities 4, 8 and 12 g/L (7.9, 7.4 and 7.6 Kg/m3, respectively) differed only the lower salinity proposal (0 g/L). Survival, which ranged between 97 and 100% without statistical difference between treatments (p≥0,05), was not impaired with increasing salinity. In relation to animal welfare, glucose was shown to be higher in fish undergoing treatment 16 g/L (76.0 mg/dL) and above the reference values for the baseline on fish (<60.0 mg/dL). However, hemoglobin and hematocrit concentrations were not significantly different between treatments (p≥0,05). The weight and length data indicated smaller dispersion in the treatment 4 g/L. Growth coefficients (b) show differences in the degree of allometry in the treatment 0 (2,967), 4 (2,969) and 16 g/L (2,796), relative to treatment 8 (3,020) and 12 g/L (3,020). With these results, it is concluded that salinities above 4 g/L can interfere in the control of water quality variables; salinities of 8 and 12 g/L can adversely affect the growth performance and, fish welfare can be compromised in salinity 16 g/L.