Salinity tolerance and water ionic balance in Macrobrachium jelskii post-larvae

Abstract

Considering that salts are widely used in prawn farming and that studies on their impacts on the aquatic ecosystem have not been identified, this study aimed to evaluate the possible changes caused by acute exposure of Macrobrachium jelskii prawn to sodium chloride and salt marine, through acute toxicity test and histopathological study. Prawn postlarvae (0.2112±0.34 g) were exposed to different concentrations of NaCl, 0 (control) to 26‰; and sea salt, 0 (control) to 35‰; for 96 h. In each duplicate treatment, seven prawns were kept in 2 L beakers for 96 h, with temperature, photoperiod, and pH-controlled, without any loss in the control group. To estimate the median lethal salinity (LS50-96h) the “Trimmed Spearman Karber method” program was used. The LS50-96h for NaCl was estimated to be 14.50‰ with a safety level of 1.45‰ and for the sea salt LS50-96h of 26.35‰ with a safety level of 2.63‰. It was also observed that at the concentration of 23‰ of artificial marine salinity, no mortality was observed, reflecting a narrow line between innocuous and deleterious salinity for M. jelskii post-larvae. At the end of the acute toxicity tests, the prawns were fixed and processed for staining in Hematoxylin and Eosin (H.E), Periodic acid-reactive Schiff (P.A.S), Blue Alcian (A.B), and Immunohistochemistry. For branchial histopathological studies, their histological sections were evaluated with an optical microscope. The main branchial alterations observed were hyperplasia, hypertrophy, cellular swelling, detachment of the respiratory epithelium, pillar cell rupture, some secondary lamella fusions, and necrosis.