Abstract
The osmoregulatory ability and salinity tolerance of four species of decapod crustaceans (Decapoda: Natantia) were evaluated to test the degree of physiological adaptation to variations in salinity (2 d exposure to 10, 20, 25 and 32. The ecophysiological salinity tolerance of two penaeids (Metapenaeus joyneri and Penaeus semisulcatus) and two palaemonid species (Palaemon pacificus and Exopalaemon orientalis), representative of natant crustacean species inhabiting coastal shallow-water environments were evaluated. Our results show that both E. orientalis and P. pacificus are tolerant of all salinities tested here due to displaying both hyper-/hypo-osmoregulatory ability (in low and high saline waters, respectively), consistent with osmoregulatory patterns displayed by other species in the family (Palaemonidae). The two penaeid species evaluated here displayed efficient hyporegulatory ability in full-strength seawater; however, high mortality was observed in both species at low salinity exposure (10) (73% and 87% mortality for M. joyneri and P. semisulcatus, respectively). In terms of salinity tolerance and thus osmoregulatory ability (which is the mechanism of euryhalinity) of the four species, the following relative order could be assumed: Palaemon pacificu > Exopalaemon orientalis > Metapenaeus joyneri > Penaeus semisulcatus.
