Efeito da salinização artificial na produção de juvenis de camarões Litopenaeus vannamei (Boone, 1931) em sistema de mínima troca de água

Abstract

Litopenaeus vannamei, popularly known as Pacific white shrimp, leads the ranking of the most produced crustacean species in the world, which has been cultured mostly in coastal areas. However, due to the high costs of implantation, environmental conflict problems, disease outbreaks there is a migration of production of marine shrimp to inland waters with mesohaline and oligohaline waters. The waters of these regions come from lakes, wells, rivers, dams and underground aquifers, presenting great variation in their ionic composition (cations and anions). However, these ions need their proportions to be adjusted to values similar to those of seawater, so that the shrimp have a good zootechnical development during culture, promoting greater osmotic comfort to the animals, balancing energy expenditure. The ionic compensation performed by means of mineral fertilizers in the water can be quite expensive depending on the volume applied, as an alternative to reduce these costs is the use of systems with minimal water exchange, offering a reuse of the minerals used, as well as a reduction in the disposal of water and less reinvestment in the application of mineral fertilizers. Therefore, this study aimed to evaluate different forms of artificial salinization of water for the production of juveniles of marine shrimp L. vannamei in a synbiotic system for 40 days, in experimental units of 60 L, with a density of 2000 PL's m³. Four treatments in triplicate using a completely randomized design were established: SD - diluted seawater; LCSM - Low cost salt mix with freshwater; CS - Commercial sea salt and SW - sea water. A previous study was carried out on the mineral efficiency regarding the ions available in the culture water and later artificially salinized was carried out to obtain a salinity of 2.5 g/L and the proportions of cations and anions. An artificial substrate of Anomalocardia brasiliana shells (1% of the total volume of the experimental unit) was used in each experimental unit to accelerate the nitrification processes. in addition to the addition of a commercial mix of Bacillus-based bacteria in water and feed. To verify the resistance of shrimp juveniles, an ammonia stress test was carried out at the end of the culture and, also, microbiological analysis were carried out at the beginning and end of the experiment for the total count of Vibrio spp. and fungi Juvenile intestinal. The use of the artificial substrate together with the synbiotic system proved to be effective in the control of nitrogen compounds with an average of 0.21 mg NAT/L and 0.32 mg N-NO2/L. The values of calcium, magnesium and total hardness remained above 30, 75 and 400 mg/L, respectively, in all treatments and the total alkalinity maintained its values above 120 mg CaCO3/L. Regarding the survival parameters in the treatments with low salinity significant differences were observed between the treatments, with a greater survival in the LCSM treatment. The final average weight observed in the low salinity treatments were higher than the value found in the seawater treatment, however the other variables of zootechnical performance were similar. The use of Bacillus-based probiotic in the water and feed offered to the shrimp in this work, proved to be efficient in the colonization of the intestinal microbiota of shrimp cultured in all treatments. Thus, the different forms of artificially salinized obtained similar results in terms of zootechnical development and resistance to ammonia stress when compared to seawater.