Dynamics of Salinity Adaptations in the Euryhaline Crayfish Pacifasticus leniusculus

Abstract

Crayfish acclimated to fresh water (FW) maintain hemolymph osmotic and ionic concentrations significantly above those in the medium by a combination of active ion uptake and reabsorption of ions from the urine. This pattern appears to persist even as hemolymph osmolality approaches the isosmotic line between 350 and 475 mosm, with new equilibrium values being reached after 3 wk. Animals transferred from 350 to 750 mosm underwent a transient period (48 h) in which hemolymph was hypoosmotic to the medium, but this disappeared over 3 wk as hemolymph became isosmotic. The activities of the two major transport enzymes, the Na/K ATPase and carbonic anhydrase (CA), in both the gills and the antennal gland were also dependent on environmental salinity. CA in both tissues increased on transfer from 475 mosm to FW but not from 475 to 750 mosm. There were no short-term changes in CA activity; rather, it appears that new enzyme was induced over a 3-wk period. CA activity was reduced in animals transferred from FW to either 475 or 750 mosm. The changes occurred over a 3-wk period, which was consistent with protein turnover rather than activation/deactivation. Changes in the Na/K ATPase activities were less pronounced, and they appeared to be regulated over both the short term (activation/ deactivation) and long term (induction/deinduction).