Cultivation of the Pacific white shrimp Litopenaeus vannamei(Boone, 1931) in low salinity with biofloc technology (BFT): Effect of different concentrations of sulfate
The Pacific white shrimp Litopenaeus vannamei is an eurihaline species, being an option to grow it in low salinity. In places where water is scarce and / or the land is expensive the biofloc system (BFT) is a cropping system option because it is possible to reuse water from the farming. In general, the ionic composition of water is more important than salinity. Sulphate is the third most abundant ion in seawater and plays an important role in osmoregulation, detoxification and consequently in the survival and growth of shrimp. The aim of this study was to determine the adequate concentration of sulfate for L.vannamei reared in BFT system at low salinity during the nursery and growth phase. For this, six treatments and four replicates with different concentrations of sulfate were defined: control treatment was used seawater diluted to salinity 5 (AM 5), in treatments with artificial salinization, and with salinity 5, the nominal sulfate concentrations were 784mg / L (SA 2); 392 mg/L (SA1); 196 mg/L (SA 0.5); 98 mg/L (SA 0.25) and 49 mg/L (SA 0.12). The experiment lasted 78 days, with 35 days in nursery phase and 43 days in grow out phase. At the nursery and growth phase, shrimps were stocked in densities of 1500 shrimps/m3 and 500 shrimps/m3, respectively. After the end of the experiment the data of water quality, zootechnical performance and histology were analyzed, such as CAA, GPS, TCE, biomass, final mean weight, 3 productivity / m , survival and gills. During the experimental period, water quality was maintained within the ideal for shrimp L. vannamei cultivation, except total suspended solids. There were no significant differences in zootechnical performance between treatments (P>0.05) in nursery phase, while in the grow out phase, the productivity was lower in the tratament SA 0.12. The results of the histology show that the lower the sulfate concentration, the larger the damages caused in the gills of the shrimp. This study showed that the 50% reduction in the sulphate concentration in the artificial salt water had a better result when considering the experimental time, cost, histology, zootechnical performance and growing conditions.