The Relationship between Gill NaK-ATPase Activity and Osmoregulatory Capacity in Various Crabs

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Abstract
NaK-ATPase activity of gills was determined in five species of euryhaline crabs placed in varying seawater (SW) concentrations for 1 week. Enzyme activity was highest in the gills of two semiterrestrial grapsids, Metopograpsus thukuhar and Cyclograpsus henshawi; intermediate in two osmoregulators, Thalamita crenata and Panopeus herbstii; and lowest in an osmoconformer, Calappa hepatica, when all animals were placed in 100% SW. When animals were placed in 50% SW, large increases in enzyme activity were noted in P. herbstii and T. crenata but no change was noted in the osmoconforming C. hepatica or the semiterrestrial M. thukuhar and C. henshawi. Enzyme activity is concentrated in the three most posterior gills of T. crenata with major increases in activity in these gills when animals were placed in diluted seawater. It is suggested that gill NaK-ATPase is associated in the osmoregulatory capacities of these crabs and that the enzyme is functioning both in the uptake of salts in hyperregulation and in the extrusion of salts in hyporegulation in crabs.

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