Water and ion balance in the tissues of the dehydrated cockroach, Periplaneta americana

Cockroaches dehydrated for 8 days lost nearly 50% of their haemolymph volume and approx 25% of their tissue water. Haemolymph osmolality and sodium, potassium, and chloride concentrations in the haemolymph and tissue water were all regulated within narrow limits. It is confirmed that sodium and potassium ions are sequestered within the fat body during periods of dehydration. The increase in sodium and potassium ions in the fat body is shown to arise from ionic regulation of haemolymph and other tissues. During periods of rehydration, sodium and potassium concentrations decrease in the fat body and haemolymph volume and ionic concentrations return to near original levels. A small proportion of the surplus haemolymph chloride ions is shown to be associated with the cuticle during times of water deprivation.