Salt levels linked to increased carbonic anhydrase enzyme in the gills of green crabs that tolerate different salt waters

The euryhaline green crab can maintain hemolymph osmolality up to 300 mOsm higher than the surrounding medium when acclimated to low salinity.

• The transition from osmoconformity to osmoregulation occurs at a critical salinity of 26 ppt.
• New hemolymph osmotic and ionic levels are established within 12 hours after transfer to low salinity.
• An 8-fold increase in the enzyme carbonic anhydrase (CA) is observed in the gills during this transition.
• CA induction primarily occurs in the cytoplasm of the posterior gills, with some induction in the membrane-associated fraction.
• Inhibition of branchial CA activity leads to decreased hemolymph osmotic and ionic concentrations in crabs acclimated to low salinity.
• CA gene expression is activated following exposure to low salinity, with increased mRNA levels at 24 hours and elevated protein activity at 48 hours.

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