Differential induction of branchial carbonic anhydrase and NA⁺/K⁺ ATPase activity in the euryhaline crab, Carcinus maenas, in response to low salinity exposure

Activity of carbonic anhydrase (CA) and Na/K ATPase is regulated in response to changes in salinity, with CA activity peaking at seven days after transfer to low salinity.

• Carbonic anhydrase activity in crabs acclimated to high salinity was low but increased significantly in the posterior gills after exposure to low salinity.
• Na/K ATPase activity was initially high in crabs acclimated to 32 ppt salinity and did not increase further after transfer to 10 ppt salinity.
• In crabs acclimated to hypersaline conditions (40 ppt), a transfer to low salinity resulted in a four-fold increase in Na/K ATPase activity by seven days.
• Both enzymes respond to low salinity, but the degree of salinity change required for their induction differs.
• Crabs exhibited hemodilution and cell volume adjustments in response to low salinity exposure prior to the induction of enzyme activity.

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