Salinity effects on gill (Na⁺, K⁺)-ATPase activity in the semiterrestrial crab Goniopsis cruentata (decapoda,...

The remarkable diversity of decapod crustaceans inhabiting a wide range of osmotic environments reflects their evolutionary success, likely driven by the variety of mechanisms for body fluid regulation involving both molecular and systemic adaptations. In recent decades, considerable research has focused on the osmoregulatory strategies of decapod crustaceans occupying distinct osmotic niches. However, limited information is available on the effects of salinity on the activity and expression of gill (Na⁺, K⁺)-ATPase in terrestrial and semi-terrestrial species. This study investigates key aspects of osmoregulation in the semiterrestrial crab Goniopsis cruentata during acclimation to varying salinity levels. After exposure to 10, 20, 30, and 40 ‰S for 5 days, the crabs exhibited strong hyper- and hypo-osmoregulatory capabilities, reaching isosmotic conditions at approximately 30 ‰S. The Total Regulatory Capacity, expressed as a dimensionless ratio of hemolymph to external osmolality variation, was 0.08, with hyper- and hypo-osmoregulatory values of 0.06 and 0.12, respectively. Goniopsis cruentata demonstrated increased mRNA expression of (Na⁺, K⁺)-ATPase under hypo-osmotic conditions, despite a concurrent reduction in enzyme activity. These findings suggest that both hyper- and hypo-osmoregulatory mechanisms in G. cruentata are dependent only minimally on branchial (Na⁺, K⁺)-ATPase activity and instead rely more strongly on other ion transporters to maintain body fluid homeostasis. These results contrast with observations in aquatic crabs, in which branchial (Na⁺, K⁺)-ATPase plays a central role in osmoregulation.