3) Effects of ambient ammonia on the nitrogen metabolism of the freshwater crayfish Cambarellus montezumae

Ammonia and urea fluxes, muscle ammonia and blood ammonia, urea, and protein levels were measured in the crayfish Cambarellus montezumae challenged to 500, 1000, 2000 and 4000 µmol NH 4- N L -1 over a 4 h period. The principal objective was to evaluate changes in the nitrogen metabolism of this species when challenged by ambient ammonia levels similar to those that might be encountered in its natural environment. The data obtained indicates that the mean ammonia efflux rate of this species, under control conditions, was1.71±0.47 µmol gr -1 h -1. After 1 h post-exposure only the animals exposed to 500 µmol NH 4 -N L -1 showed an ammonia influx. Blood ammonia at control conditions was 82.9 µmol NH 4 -N L -1, however, after 4 h of exposure to the above ambient ammonia levels, a rise in blood ammonia was produced up to 143.8, 223.5, 544.6 and 980.8 µmol NH 4 -N L -1, respectively. A non-significant change in total haemolymph protein and urea efflux rate was found. Mortalities were nil during experimental conditions, which seems to indicate that Cambarellus montezumae is a species able to cope with high ambient ammonia levels.

Keywords: ammonia fluxes, urea fluxes, haemolymph ammonia, nitrogen metabolism, Cambarellus montezumae.