AMMONIA DYNAMICS DURING AND AFTER PROLONGED EMERSION IN THE FRESH-WATER CLAM CORBICULA-FLUMINEA (MULLER) (BIVALVIA, CORBICULACEA)

Hemolymph ammonia content during emersion and ammonia fluxes on reimmersion were examined in the freshwater bivalve Corbicula fluminea (Muller). Hemolymph ammonia levels remained at pre-emersion levels over a 5-day emersion period at 25-degrees-C, but thereafter levels increased prior to death. On resubmergence after 3 days emersion, the initial rates of ammonia excretion were low and took 15 h to reach maximum levels. Duration of emergence did not affect postemergence ammonia excretion rates in individuals emersed for less than 3-4 days. These results indicate a lack of ammonia accumulation in aerially exposed specimens. Rather, C. fluminea appeared to suppress protein catabolism during emergence and avoided ammonia accumulation. Death on emergence occurred coincidentally with an increase in ammonia accumulation. After reimmersion, the delay in development of ammonia efflux maxima may represent metabolic "switching" from catabolism dominated by nonprotein energy stores to one partially supported by protein. Suppression of protein catabolism in air is an adaptation to the prolonged and unpredictable emergence not previously reported for any freshwater species.