Inhibition of ammonia excretion and production in rainbow trout during severe alkaline exposure

Exposure of fish to alkaline conditions clearly inhibits the rate of ammoni a excretion (J(AMM),) leading to problems of ammonia accumulation and toxic ity. There is some evidence that higher environmental calcium levels may am eliorate the negative effects of alkaline exposure. In the present study, w e investigated the effects of elevated environmental calcium on the recover y of ammonia excretion during acute (6 h) and chronic (15 day) exposures to high pH (pH 10), and the levels of nitrogenous products (ammonia, urea, an d glutamine) in tissues and plasma (1-15 days). Acclimation to alkaline con ditions results in a chronically depressed ammonia excretion rate. Glutamin e as well as urea do not appear to be important in ammonia detoxification a nd storage. Calculations of the production rates from storage and excretion data indicate a reduction in the rate of ammonia production. Elevating env ironmental calcium during acute exposure to alkaline conditions does not af fect the recovery of J(AMM), but may reduce stress. We conclude that rainbo w trout survive alkaline exposure by reducing ammonia production and that t he role of calcium may be in the amelioration of the stress of alkaline exp osure. (C) 1998 Elsevier Science Inc. All rights reserved.