Nitrogen Excretion in Marine and Fresh‐water Crustacea

Abstract

Summary 1. The major characteristic of aquatic Crustacea is ammonotelism as shown by the relative importance of various nitrogenous end‐products of their nitrogen metabolism. 2. In contrast to urico‐ and ureo‐genesis pathways, ammoniogenesis pathways have received recent attention; some specific enzymes such as glutamate dehydrogenase, AMP‐deaminase and glutaminase are now admitted to play a possible key role in ammoniogenesis of various crustacean species. 3. Processes involved in ammonia output through the gill epithelium (diffusion and/or ionic exchanges) are discussed though few data related to Crustacea are as yet available compared to those obtained in ammonotelic fishes. 4. The effects of some environmental factors as well as the physiological state of animals on nitrogen excretion of Crustacea are envisaged. The effects of temperature, salinity and NH4 concentration in the external medium are discussed first, followed by the changes in nitrogen excretion associated with the moult cycle, the nutritional state of animals and possible neuroendocrine control. It is demonstrated that the response of the excretion rate to these factors presents various patterns according to the species, its osmoregulatory abilities and its body reserves. Changes can also occur in the requisite metabolic pathways, thus increasing the difficulty of generalization. 5. In spite of the great diversity encountered within Crustacea an attempt to bring out general trends of their nitrogen excretion is proposed. 6. The present review is focused on metabolic and physiological aspects of crustacean nitrogen excretion but the significance of nitrogen release in nutrient regeneration in marine and fresh‐water ecosystems is foreseen.

Fluxes of haemolymph ammonia and free amino acids in Mytilus edulis exposed to ammonia

“…Because of its small size and neutrality, NH3 was long considered to be the main form which freely permeates the gill epithelium. Several works have now demonstrated the permeation by both the ionic and non-ionic forms (Goldstein et al 1982, Cameron 1986, Regnault 1987, Wilson et al 1994. According to Cameron (1986), the mode of diffusion varies interspecifically, but there is a general paucity of data relating to molluscs in general or mussels in particular.…”

“…The pNH3 gradient started to become negative on exposure to external ammonia levels 23.2 mM, which suggests that when a threshold, internal NH,-N load is exceeded (blood NH4-N 2.0 mM), a n active pump functioning to extrude NH,+operates to mitigate increased diffusional influx. This extrusion of NH4+ may be coupled to an influx of Na', and many studies have provided supporting evidence for a carrier-mediated Na+/NH4+ exchange in marine or H+/NH4+ in freshwater species (Maetz 1973, Cameron 1986, Regnault 1987, Wilson & Taylor 1992. Unfortunately, apart from the investigations of Mangum et al (1978), data on the mechanism of ammonia fluxes in molluscs are limited.…”

Hemolymph ammonia and urea and nitrogenous excretions of Scylla serrata at different temperature and salinity levels

“…4B). Regnault (1987) reported that in decapod crusStatistical analysis indicated that there were signifitaceans, nitrogen was excreted mainly as ammonia cant effects of temperature and salinity on hemolymph that accounted for 60 to 70 % of total excreted nitrogen, ammonia-N and urea-N, and that there was a significant amino acids that accounted for 10% of total excreted nitrogen, and small amounts of urea and uric acids. Ammonia-N excretion is considered an indicator which reflects protein and …”

“…In crustaceans, nitrogenous excretion is affected by both extrinsic factors, such as temperature and salinity, Table 2. Scylla serrata The percentage of ammonia-N excretion (ANE), urea-N excretion (UNE), nltrite-N excretlon (NINE), nitrate-N excretion (NANE), and organic-N excretlon (ONE] from nltrogenous excretlons of crabs maintained at dlfferent salinit~es (S) and temperatures (T) and intrinsic factors, such as molt cycle, nutritional level and neuroendrocrine control (Regnault 1987, Chen et al 1994. Since the crabs used in the present study were at the intermolt stage and had been fasted for 1 d , they were considered to be at the same nutritional level.…”

“…In decapod crustaceans, ammonia, amino acids and urea are the 3 main end-products of nitrogen metabolism and are released mainly through the gill epithelium (Regnault 1987). Among nitrogenous wastes, ammonia-N (un-ionized plus ~o n i z e d ammonla as nitrogen), which 1s the least expensive with regard to energy expenditure, makes up 86% of total excreted nitrogen in the shore crab Carcinus rnaenas (Needham 1957).…”