Osmoregulation in the Lobster Homarus americanus

Abstract

Lobsters took 72 hr to adapt to a salinity of 20‰, with urine becoming markedly hypoosmotic to the blood during the first 25 hr, then increasing in concentration over the next 48 hr, though remaining significantly hypoosmotic to the blood. Adaptation to a salinity of 37‰ took 24 hr: the urine became almost isosmotic with the blood: the gastric and rectal fluids became hyperosmotic to the blood. Blood freezing-point determinations showed that over the salinity range 20–37‰ the lobster is able to osmoregulate to a limited extent only towards the lower end of the range, being otherwise an "osmocon-former." Salt-loading experiments indicated that the excess salts were rapidly excreted into the gut. It is concluded that the antennal glands are at least partly responsible for elimination of excess water, but that the gut is the site of salt excretion, and that there is rapid adjustment of salt imbalance.