Relationship between the coastal origin of the freshwater prawn Macrobrachium amazonicum and salinity levels in the hatchery

Abstract

In the culture of crustacean larvae, the best survival rates are observed at optimal salinity due to the lower expenditure of energy for osmoregulation. In optimal conditions, greater longevity is expected under conditions of complete starvation. In the present study, larvae were obtained from ovigerous females of the freshwater prawn Macrobrachium amazonicum captured in two distinct regions of the Amazon coast of Pará, representing Amazonian várzea (Abaetetuba) and estuarine (Bragança) habitats. The larvae were maintained under starvation conditions, and from the zoea I to the zoea VII stages, they were exposed to salinities of 0, 2, 5, 10, 20 and 30 ppt. Based on the results of these trials, the larvae (100 larvae/L) were then reared in a dynamic closed system in 2L tanks at salinities of 5, 10 and 20 ppt, being fed with Artemia nauplii. In the larvae captured in estuarine habitats, longevity was greatest at a salinity of 10 ppt (12.00±0.79 days) and lowest in freshwater (6.77±3.47 days). In the várzea larvae, longevity was greatest at salinities of 2 (10.33±1.97 days), 5 (10.80±2.07 days) and 10 ppt (10.23±1.07 days). Other important differences were observed between the two groups of larvae. None of the estuarine larvae molted to the PL stage in freshwater and productivity was greatly reduced (43.2±7.8 PL/L) at a salinity of 5 ppt. By contrast, the várzea larvae developed into post-larvae (PL) normally in freshwater and could be reared at salinity 5 ppt with no loss of productivity. This permitted the minimization of management costs.