Shrimps do not feed when moulting. Feeding drops abruptly during the moulting process, tbe extent of which depends on how widespread and simultaneously it has occured in the population. This can be readily observed from the feed monitoring trays. A decrease of up to 30% in the feed demand is normal when there is mass ecdysis. Appetite resumes after 1-3 days, above the previous level. Sudden changes in the environment induce shrimps to moult. Its occurence is therefore influenced by water management. Mass moulting is induced by massive but not so frequent water changes. On the contrary, frequent water changes hinder simultaneous moulting. Feeding rations should be reduced when mass ecdysis is expected (Cruz, 1991).