Improvement of the cultivation of the marine shrimp Litopenaeus vannamei in oligohaline waters dominated by bioflocs
The L. vannamei production in inland oligohaline waters (IOW) in Brazil is concentrated in the Northeast region, where the ionic composition of water is considered in the selection of cultivation areas and the management of water resources scarce in the region.Inland and marine waters present distinct ionic concentrations, which may affect the physiological processes of marine shrimps and the productivity of crops, especially in the initial phases where the acclimatization of animals to inland water conditions occurs. The constant correction of alkalinity requires the use of alkalinizing compounds adequate to the conditions of the production systems. In Chapter I, a bibliographic survey on the cultivation of L. vannamei in IOWs was conducted and the applicability of closed cultivation systems was demonstrated as a way to reduce water demands in semiarid regions, increase productivities and promote the socioeconomic development of these regions. Chapter II evaluated the characteristics of L. vannamei production in IOWs inNortheastern Brazil in order to direct the prospecting of new areas. Data were collected in the states of Ceará, Rio Grande do Norte and Paraíba, totaling 28 shrimp farms. The water samples were classified by salinity according to the Venice System, in freshwater, oligohaline and mesohaline and the ionic compositions and the production data of the shrimp farms compared. Through salinity, electrical conductivity (EC) and ionic composition, the uses of water for irrigation and human consumption were evaluated.Most of the properties were supplied with oligohaline and mesohaline waters from rivers or wells, where 78% of them were considered unsuitable for irrigation. The average ponds area was 1.30 ± 1.08 ha. The samples when compared to diluted sea water, showed that Na and SO4 were in a lower proportion (%), while Mg , Ca and HCO3 were in a higher proportion, independent of the saline class. The ionic ratios, Mg2+:Ca2+ and K+:Ca2+ were below ideal in all classes, while Na+:K+ in oligohaline waters were on average adequate for the species. Oligohaline and mesohaline waters are more favorable for shrimp culture, as they have less uses. In addition, these waters have alkalinities and total hardness superior to freshwaters and higher productivity can be achieved in them. Through the data of Chapter II, an artificial salting representative of the farms investigated was formulated, called Low Salinity Ionic Composition (LSIC). In chapters III and IV before the experiments, the water with the LSIC was fertilized with NH4Cl to develop a bacterial inoculum. The experiments were performed in the nursery phase in an oligohaline medium dominated by bioflocs. The post-larvae were fed commercial diets. Water temperature (T°C), pH, dissolved oxygen (DO), nitrogenous compounds (N- AT, N-NO2- and N-NO3-), orthophosphate, total alkalinity (TA), total hardness (TH), salinity, EC, total suspended solids, and the concentration of major ions were monitored. Zootechnical performance was evaluated by mean final weight, survival, specific growth rate, weekly weight gain, productivity and apparent feed conversion. Chapter III used marine water inoculation for ionic water correction with LSIC. The study lasted 27 days where 20 tanks of 150L were used, with 150 post-larvae of 0.06g each. Four treatments were tested with inoculation (3, 6, 10 and 13%) and one treatment without (0%), with four repetitions each. Among the nitrogen compounds only N-NO3- reached above safe concentrations in all treatments. The zootechnical performance was superior in the inoculated treatments, not differing from each other. The results are associated with the increase of Na+, Mg2+ and K+ ions and the Na+:K+ ratio. It was observed that 3% of the inoculum can mitigate the negative effects of ion imbalances of oligohaline waters on the development of PLs of L. vannamei. Chapter IV evaluated the effects of alkalinity and the alkalinizing compound used, on the ionic composition of the water and on the zootechnical performance of L. vannamei. The study lasted 40 days and was developed in waters with LSIC with 0.5% of a marine brine. The treatments tested hydrated lime or sodium bicarbonate (NaHCO3 ) in the maintenance of 75, 150 and 300 mg of CaCO3L alkalinities, with three repetitions each, 18 tanks of 50 L populated with 60 post-larvae ofL. vannamei with an average weight of 0.02g were used. Among the nitrogen compounds- 2+only N-NO3 reached inadequate values in all treatments. The TH and Mg were higher where the total alkalinity of 300 mg of CaCO3 L-1 was maintained with hydrated lime (Ca300), as well as the survival of the animals and the productivity of the system. The use of hydrated lime in the higher concentration elevated the alkalinity beyond total hardness, protecting the animals from the toxic effects of N-NO3-, compensating the removal of Ca2+ from the water by the animals during moulting and thus generating adequate conditions for the development of L. vannamei in the nursery phase in an oligohaline environment dominated by bioflocs.