Abstract

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 ?mol NH₄-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, was 1.71±0.47 ?mol gr^-1 h^-1. After 1 h postexposure, only the animals exposed to 500 ?mol NH₄-N L^-1 showed an ammonia efflux, all other groups showed an ammonia influx. Blood ammonia at control conditions was 82.9 ?mol NH₄-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 ?mol NH₄-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.

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