ROER, R.*; LI, T.; VANA, M.; PATE, S.; CHECK, J.; Univ. of N.C. at Wilmington: Effect of size and salinity on sodium and water permeability and gill Na,K-ATPase activity in the blue crab, Callinectes sapidus.

Juvenile blue crabs are found in large numbers in the oligohaline regions of the Cape Fear estuary. Crabs collected from 209 mOsm (carapace width of 13.6 +/- 3.0 mm) had a hemolymph osmolality of 621.0 +/- 90.0 mOsm. Crabs (17.1 +/- 7.0 mm, from medium of 75 mOsm) had a hemolymph osmolality of 664.6 +/- 30.3 mOsm. Thus, juveniles maintain hemolymph hyperosmotic to the medium to the same extent as adults. With a larger surface-to-volume ratio than adults, maintaining such a gradient presents a challenge to the juveniles. Adaptations may include a lower permeability and/or higher levels of transporting enzyme activity in the gills of juveniles. Permeabilities were measured by efflux from crabs pre-loaded with 22-Na or 3-H water. Effluxes increased with increasing body weight at both 1000 and 150 mOsm. The slope of the log-log plot of fluxes vs. body weight was ~0.9. For all sizes, water permeability decreased by 91% (P < 0.002) with transfer from 1000 to 150 mOsm. Na permeability decreased with acclimation salinity; large crabs had an 88% decrease (P < 0.001), small crabs had an 83% decrease (P < 0.001). The permeability was significantly (P < 0.005) lower for larger crabs at 150 mOsm than for small crabs. The activity of gill Na,K-ATPase activity showed a discontinuous distribution as a function of size. Crabs with body weights < 5g had substantially higher activity than larger crabs. Anterior gills of small crabs had 10.6 times the Na,K-ATPase activity as those of larger crabs in 1000 mOsm, and 9.5 times the activity at 150 mOsm. Posterior gills from small crabs at 1000 and 250 mOsm had 25.6 x and 15.6 x the activity, respectively, as those of larger crabs at those salinities (P < 0.001).