Some effects of hypoxia and medium ammonia enrichment on efflux rates and circulating levels of ammonia inNephrops norvegicus

Abstract

Abstract. Eutrophication has been reported for autumn months in regions of the Kattegat/Skagerrak, causing stress to bottom-living organisms. The present studies, undertaken in April (1989), investigated the effects of hypoxia and high ammonia levels in the burrowing decapod Nephrops norvegicus (L.). The net ammonia efflux rates and circulating ammonia levels at 6 and 12°C, at normoxia [partial pressure of 02 in the water (torr), Pw02 = 155 torr)] and hypoxia P, vO2 = 24 torr) in normal seawater and ammonia-enriched (300 #mol ammonia 1-t) seawater were examined. The hourly weight-specific efflux rates were very variable and in all groups included some individuals which showed periods of no net efflux, or even a net uptake of ammonia. At each temperature, net efflux-rate differences due to treatments were not significant (P>0.05; ANOVA, in all cases) and only the differences between the net efflux rates of the normoxic groups were significantly affected by temperature (P < 0.05; ANOVA). Circulating ammonia levels were also variable, and at 6°C the ammonia-enriched groups had significantly higher weight-specific blood ammonia content values than the normoxic group (P < 0.05 in both cases). A net uptake of ammonia occurred in ammoniaenriched conditions -probably along a reversed NH4 + gradient, as downhill pNH 3 gradients were maintained in all groups -and may represent the only means by which some branchial efflux of ammonia could proceed.

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

“…In contrast to the findings on other species (e.g. Hosie et al 1991), an apparent ammonia influx was found here with M. edulis exposed for only 5 min in seawater containing 3.2 or 6 mM NH,-N. The influx rates pertaining to 5 min were relatively higher (p < 0.05) than those measured during the following 2 h, as shown in Fig.…”

“…This facilitated transport may be confused with active transport, which exhibits Michaelis-Menten kinetics. It has been shown that marine fish (Wilson & Taylor 1992) and crustaceans (Cameron 1986, Hosie et al 1991) are able to maintain reversed pNH, and NH4+ gradients when external levels are elevated. In these cases, it was concluded that some form of active NH,+ extrusion must be operating in order to counteract an inward diffusion of NH3 and NH4+.…”

Effect of a severe hypoxia on some aspects of nitrogen metabolism in the crabcancer pagurus

“…In regularly fed and resting Nephrops norvegicus exposed to a PwO2 of 16 Torr for 5h, a 65-70% decrease in ammonia excretion rate was observed by Hagerman etal. (1990), although this was not corroborated by recent observations of these authors (Hosie et al 1991). However, a 25-35% decrease in the blood ammonia content of N.norvegicus following 5h of severe hypoxia was noted by these authors in both studies.…”

Effect of dietary protein level on growth, survival and ammonia efflux rate of Litopenaeus vannamei (Boone) raised in a zero water exchange culture system

“…Our results seem to support this observation, because once bacteria established within the system after day 14, ammonia started to decrease while nitrite started to increase (Figs 1a, b and 2a). However, ammonia is a small molecule with high solubility, so it can easily diffuse across biological membranes and when crustaceans are exposed to water with greater ammonia levels than those occurring in the haemolymph, an influx‐induced elevation can occur, lowering the ambient ammonia level as reported by Hosie, Uglow, Hagerman, Sondergaard and Weile (1991), Schmitt and Uglow (1997) and Gómez‐Jiménez and colleagues (2002). Although both facts have been previously reported, at this time it is not possible to elucidate whether the decrease in water ammonia levels after day 13 of dietary treatments in our zero water exchange systems (Fig.…”

“…1a and b), just 1 day before the highest ammonia efflux rate was measured. It has been reported by Hosie and colleagues (1991); Regnault (1992); Schmitt and Uglow (1997) and Durand and Regnault (1998) that when crustaceans are loaded with ammonia either by exposure to ambient ammonia or deprivation of environmental seawater, following reimmersion, the rates of ammonia excretion are enhanced during the first hours and the time taken to reach baseline ammonia excretion rates varies for species and experimental conditions. Our results seem to suggest that the 25% experimental group was, for some unknown reason, more susceptible to the environmental ammonia load and therefore in this group the highest ammonia excretion rates were recorded.…”