| Resumo: |
Compared with other countries, the Brazilian shrimp aquaculture had a moderate development occupying an area of less than 25,000 hectares. However, shrimp production has accelerated in Northeast region in recent years, due to increasing domestic demand and improvements in farming technology. This Region is responsible for around 97% of the national shrimp production. The inland farming of Penaeus vannamei in low-salinity waters is a recent development in some municipalities in the state of Ceará. However, there is little information pertaining to the suitability of waters with various ionic compositions for shrimp culture. The purpose of this study was to investigate the effects of dietary supplements of NaCl on growth, survival, haemolymph osmolality and total hemocyte count of P. vannamei. This study addressed two questions. In trial 1, earthen pond-reared P. vannamei at intermoult stages and ranging from 5 to 20 g were sampled at intervals for determination of haemolymph osmolality. Haemolymph osmolality was not influenced by the increased weight of shrimp. Haemolymph osmolality of juveniles shrimp (5-20 g) were then evaluated 24 h after they had been transferred from pond water (0.5 ppt) to the seawater (35 ppt). Shrimp haemolymph osmolality increased with external salinity and ranged from 661.0 ± 25.2 mOsm/kg (D1) and 916.9 ± 40.1 mOsm/kg (D4). In trial 2, juveniles of P. vannamei reared in low-salinity water (0.3-0.5 ppt) were distributed into five groups (control, D1, and treatments, D2, D3, D4 e D5) with four replicates. All shrimps were completely randomised stocked into 20 tanks at an initial density of 25 shrimps per tank. Diets for the control (D1), D2, D3, D4 and D5 groups consisted of the basal diet supplemented with 0 g/kg, 5 g/kg, 10 g/kg, 20 g/kg,and 40 g/kg of NaCl respectively. After 22 days, differences in survival, final weight, specific growth rates (SGR) and absolute growth rate (AGR) among treatments were significant. Survival, final weight, specific growth rates (SGR) and absolute growth rate (AGR) ranged from 27.0 ± 1.5 to 67.0 ± 3.50%, 11.8 ± 0.2–12.7 ± 0.2 g, 1.1 ± 0.1–1.5 ± 0.1%/day and 0.8 ± 0.1–1.1 ± 0.1 g/shrimp/day, respectively. However, there were no significant trends in haemolymph osmolality and total hemocyte count of shrimp juveniles distributed into five groups (control, D1, and treatments, D2, D3, D4 e D5). |
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