Why are some mud crabs not full of meat?

The mud crab is a crustacean of the Portunidae (swimming crab) family. Its growth is not a continuous process, but results from a series of moults that occur when it grows to the size of its current shell. The phase between each moult is termed the 'intermoult period'. The onset of moulting is brought about through a hormonal process. A new cuticle is secreted under the old shell. The crab then rapidly absorbs water, splitting its shell along suture lines and then backs out of the old shell. Inorganic salts stored within the body of the crab are then rapidly redeposited to harden the new cuticle into a larger new shell. The fluid within the body of the crab is then replaced with meat during the intermoult period, when the crab feeds ferociously. Taking home a crab that has recently moulted may result in a disappointing end to a good day's fishing because the crab has not had a chance to fill its body cavity with flesh and will probably contain mostly liquid or a jelly mass with ...  more