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The influence of environmental factors on the nitrogenous excretion of the spot prawn, Pandalus platyceros Quarmby, Lynne Marie


There exist many conflicting reports on the influence of environmental factors on the nitrogenous excretion of marine invertebrates. In an attempt to resolve these paradoxes, the composition and rates of nitrogenous excretion of the spot prawn, Pandalus platyceros, were examined under carefully controlled conditions. The animals were incubated for relatively short periods (1 to 2 hours), keeping bacterial density to a minimum: excretion was measured by the accumulation of nitrogenous compounds in the incubation water. Although the incubation water inhibited the activity of urease, this inhibition was overcome by the use of increased concentrations of urease in urea analysis. Ammonium excretion rates of 0 to 10.5 μg-at NH₄⁺-N g⁻¹h⁻¹ were observed, while the rate of excretion of urea ranged from 0 to 5.7 μg-at Urea-N g⁻¹h⁻¹. These rates were highly dependent on temperature, salinity and diet with the effects of each factor determined by life stage. Response to temperature was more complex than changes in metabolic rates and, similarly, reduction in the rate of metabolism due to salt stress was not enough to explain the effects of salinity on nitrogenous excretion. Young prawns did not excrete as much ammonium as expected on the basis of body size. Excretion of dissolved organic nitrogen (DON), other than urea, occassionally constituted a significant proportion of the nitrogen excreted but was highly irregular and on average did not contribute significantly to the nitrogneous excretion of any study group. Diet influenced the composition and rates of nitrogenous excretion of the euphausiid, Euphausia pacifica, the amphipod Ampithoe simulans, and the shrimp Eualus pusiolus as well as P. platyceros. In each case the effect was correlated with the ratio of protein to carbohydrate in the diet. Urea was an important excretory product of each of the four species of marine Crustacea examined.

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