Gill area, permeability and Na+,K+-ATPase activity as a function of size and salinity in the blue crab,Callinectes sapidus

Jan 25, 2006Journal of experimental zoology. Part A, Comparative experimental biology

Gill size, saltwater levels, and salt-pumping enzyme activity in blue crabs

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Abstract

Juvenile blue crabs less than 5 g in body weight have markedly higher gill Na+, K+ -ATPase activity compared to larger crabs.

Juvenile crabs have a larger gill surface area relative to their body weight, which decreases as they grow.
Weight-specific water and sodium fluxes decrease with body weight, but not as significantly as gill surface area.
Acclimation to dilute seawater increases Na+, K+ -ATPase expression and activity in crabs, though the increase is less pronounced in juveniles.
The ability to maintain osmotic and ionic balance in juveniles is linked to high levels of gill Na+, K+ -ATPase activity.

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Juvenile blue crabs, Callinectes sapidus, extensively utilize oligohaline and freshwater regions of the estuary. With a presumptively larger surface-area-to-body weight ratio, juvenile crabs could experience osmo- and ionoregulatory costs well in excess of that of adults. To test this hypothesis, crabs ranging over three orders of magnitude in body weight were acclimated to either sea water (1,000 mOsm) or dilute sea water (150 mOsm), and gill surface area, water and sodium permeabilities (calculated from the passive efflux of 3H2O and 22Na+), gill Na+, K+ -ATPase activity and expression were measured. Juveniles had a relatively larger gill surface area; weight-specific gill surface area decreased with body weight. Weight-specific water and sodium fluxes also decreased with weight, but not to the same extent as gill surface area; thus juveniles were able to decrease gill permeability slightly more than adults upon acclimation to dilute media. Crabs < 5 g in body weight had markedly higher activities of gill Na+ ,K+ -ATPase than crabs > 5 g in both posterior and anterior gills. Acclimation to dilute medium induced increased expression of Na+, K+ -ATPase and enzyme activity, but the increase was not as great in juveniles as in larger crabs. The increased weight-specific surface area for water gain and salt loss for small crabs in dilute media presents a challenge that is incompletely compensated by reduced permeability and increased affinity of gill Na+, K+ -ATPase for Na+. Juveniles maintain osmotic and ionic homeostasis by the expression and utilization of extremely high levels of gill Na+, K+ -ATPase, in posterior, as well as in anterior, gills.

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Gill area, permeability and Na+,K+-ATPase activity as a function of size and salinity in the blue crab,Callinectes sapidus

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