Although Litopenaeus vannamei can tolerate a wide range of salinity (1 to 50 g/L), adequate post-larvae (PLs) acclimation is crucial for its successful farming at low salinities. The aim of this work was to evaluate the effects of different rates of salinity reduction on the survival and gill and hepatopancreas histopathology of PLs during the acclimation period.
Shrimp (21-old-day PL; n=360) were distributed in nine 5 L tanks, where they were acclimated to low salinity via its decreasing from 35 to 1 g/L within 24 hours according two salinity reduction rate treatments: A1, constant rate of 1.45 g/L/h; A2, using 0.46%/h from 35 to 5 g/L, 0.25g/L/h from 5 to 2 g/L, and 0.13 g/L/h from 2 to 1 g/L. Also, a control group was maintained at 35 g/L but with a saltwater exchange rate of 40%/h. All groups were evaluated in triplicate. At the end of the acclimation (24h) and 24 hours later (24h+), survival was determined, and PLs were collected for further histological analysis of gill and hepatopancreas following hemocyanin and eosin method.
No differences were observed for survival at 24h. On the other hand, it was significantly lower in A1 at 24h+ compared to A2 and control (Table1). Despite no difference was observed for survival between A2 and control, the former exhibited several histopathological damages compared to control. For instance, in the epithelial structure of the gill filaments was observed hemocytic infiltration and a hypertrophy at 24h and 24h+ (Fig.1B and D). Hepatopancreas of the analyzed samples, in 70% it was not possible to identify the cells (R, B, F) from A2 (Fig.1F and H). While, at 24h+, 60% from A2 exhibited ruptured epithelial cells, abnormal appearance in the structure and reduction of B and R cells (Fig. 2D). In conclusion, salinity reduction during PLs acclimation may not reduce survival but causes several histopathological damages in gills and hepatopancreas.