Osmoregulation of the xanthid crab, panopeus herbstii
1. 1. After acclimation; the mud crab, Panopeus herbstii, hyperosmotically regulates between 10 and 28 ppt and osmoconforms above 28 ppt. Chloride ion concentration remained at a relatively constant hyperionic level at lower salinities and became hypoionic at high salinities. 2. 2. The rate of acclimation to hyper and hypoosmotic shocks varied. Upon a sudden change from 27 to 19 ppt, haemolymph osmolality stabilized within 4 hr. Upon a sudden change from 27 to 35 ppt, crabs did not equilibrate their osmolality within 48 hr. Instead, haemolymph osmolality remained hypoosmotic. 3. 3. A gradual 35-23-35 ppt change in salinity over 12 hr resulted in an initial 75 mOsm decrease in osmolality. As salinity increased, the mud crab regulated hyperosmotically until 33 ppt and hypoosmotically thereafter. 4. 4. Upon exposure to a salinity cycle in the field, haemolymph osmolality remained relatively constant. Thus, P. herbstii is capable of hyper-hypoosmoregulation when exposed to short-term changes in salinity. This conclusion is not suggested by the osmotic relationship upon acclimation. © 1988.
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