Physiological aspects of molting in the blue crab Callinectes sapidus

From a respiratory and metabolic standpoint, a blue crab isin an extremely precarious condition during a molt. A molt isphysiologically possible for two major reasons. First, a premoltalkalosis anticipates the acidosis that arises during actualexuviation when the gas exchanger and ventilatory appendageare impaired and thus anaerobic metabolism must be activated.Second, the crab is able to revert to more primitive forms ofskeletal support and, immediately after exuviation, gas exchange.These mechanisms are very fragile, however, as are the cardiovascularmechanisms that provide the force for exuviation; any one mayfail. Changes in various enzyme activities and in free aminoacid content of the tissues, which are usually associated withosmotic challenges, are associated specifically with a moltas well. I suggest that they are related to isosmotic wateruptake and cell volume regulation.