The energy metabolism of common carp (Cyprinus carpio) when exposed to salt stress: An increase in energy expenditure or effects of starvation?

Stenohaline common carp (Cyprinus carpio) were chronically exposed to the t wo main osmoregulatory ions, Na+ and Cl-, at levels dose to their isoosmoti c value for 28 d (171 mM NaCl; 324 mosm kg(-1); 10 parts per thousand). The aim of this study was to assess whether or not the disturbed ion and osmor egulation affected the energy demand and the energy stores of the exposed f ish. Salt exposure reduced food intake by 70% and had adverse effects on gr owth and survival. Although food consumption decreased and growth was serio usly affected, routine oxygen consumption of the exposed fish did not drop, indicating a reallocation of energy expenditure from growth toward other p rocesses. A stress-induced increase in plasma glucose was observed. As a re sult of low food intake, lower levels of protein were used for fuel. Protei n use itself was probably replaced by the use of carbohydrates. These effec ts were confirmed by the depletion of both muscle and liver glycogen stores during the experimental period. We conclude that, besides the effects of r educed feeding, stress induced extra energy requirements leading to the dep letion of energy stores.