The present work describes the effect of different salinities on the functional morphology of the P. argentinus
hepatopancreas and analyses the tissue recovery after re-acclimation to freshwater. Adult prawns of both sexes at
sexual rest were collected from a tributary of the Mar Chiquita coastal lagoon. The prawns were acclimated in
aquaria to four salinity conditions: 0 (control), 8, 16 and 24‰. To evaluate the possible tissular recovery, after 60
days individuals from all the treatments were gradually acclimated to freshwater and maintained for other 30 days.
Hepatopancreas samples were processed at the beginning of the trial and every 30 days using standard histological
techniques for OM and TEM. The individuals from all the treatments, except the controls, showed a continuous
weight decrease, and survival was lower when higher the salinity. At 30 days from the beginning of the experiment,
hepatopancreas from 16 and 24‰ salinities showed an enlarged tubular lumen and an infolded basal lamina.
Ultratructurally, nuclear retraction, cytoplasmolysis, and RER membranes separated with electron-dense content
were observed in all the treatments except 0‰. After 60 days, profound alterations were observed with the three
treatments. After the re-acclimation period, there was no reestablishment of the functional cytology. The tolerance
to short-term salinity changes explains the capability of this prawn to inhabit in estuarine environments.
