Antoine Dosdat

Effect of chronic ammonia exposure on growth of European seabass (Dicentrarchus labrax) juveniles

Chronic effects of ammonia were studied in juvenile seabass, Dicentrarchus labrax (mean WEIGHT=11 g), exposed for 63 days to eight stable ammonia concentrations, ranging from 0.24 to 0.90 mg l−1 unionised ammonia nitrogen (UIA-N), respectively, from 6.1 to 22.3 mg l−1 total ammonia nitrogen (TA-N). Temperature (21.8 °C), pH (8.0), salinity (37.0 ppt), and oxygen concentration (over 80% saturation at the outlet) were maintained constant. Fish were fed using a self-feeder device, and they were starved during the last 8 days. Mortality of 28.9 and 42.6% occurred within the first 8 days at the two highest UIA-N concentrations, respectively, 0.90 and 0.88 mg l−1. From days 0 to 55, a 1.8- fold increase in weight gain was observed under the 0.90-mg l−1 UIA-N condition, compared to a 3.4- fold increase in the control. Weight gains were negatively correlated to ambient ammonia concentrations. Weight loss, or a transient period of growth stagnation, was observed from the onset of ammonia exposure to day 13 in seabass exposed to concentrations above 0.43 mg l−1 UIA-N. After day 13, weight gains were observed in all groups, indicating that the fish were able to adapt to increased ambient ammonia concentrations over time. By the end of the experiment, plasma ammonia levels were positively related to ambient ammonia concentrations, and oxygen consumption recorded in fasting fish was significantly dependent on ammonia concentrations. In seabass juveniles, the 0.26- mg l−1 UIA-N concentration, under an average pH of 8.0, can be considered as a safe long-term limit conditions in seawater.

Comparison of nitrogenous losses in five teleost fish species

Abstract Three species of marine fish, sea bass, sea bream and turbot, and two salmonids, rainbow trout and brown trout, were raised under similar feeding and environmental conditions in order to compare their nitrogen utilisation. Apparent digestibility of protein, ammonia and urea excretion patterns, plasma ammonia and urea concentrations and liver arginase activities were measured. No differences in protein digestibility were noticed among the five species. Ammonia and urea losses were quantitatively similar in all species, except in turbot, in which ammonia production was significantly lower. Ammonia excretion patterns were linked to ingested nitrogen and showed no inter-species differences. Conversely, urea excretion patterns were specific in turbot and sea bream. Plasma urea levels were higher in marine fish than in salmonids, with the highest values being reached in turbot. Some specificity with regard to liver arginase was also detected in the turbot. Turbot demonstrated some metabolic characteristics that could be connected with its elevated position in the phylogeny of fish.

Marine aquaculture effluent monitoring: Methodological approach to the evaluation of nitrogen and phosphorus excretion by fish

A wide range of methodologies is used for measurement of excretion by fish and for the evaluation of dissolved nutrient loadings from fish farms. In order to improve the accuracy and utility of monitoring devices, two specific apparatus have been adapted and improved: continuous sampling for simultaneous analysis and pooled samples continuous collection for later analysis. Provided that pooled samples are stabilized with 10 ml litre−1 chloroform at ambient temperature after phytoplankton and organic matter removal, these methods give similar and accurate results when applied to nitrogen-dissolved compounds, and are applicable to nutritional studies. Applied to soluble phosphate, the pooled method gives, after 72 h storage, results within 5% of the exact value. It is suitable for statistical evaluation of nutrient loadings on large-scale field studies.

Comparison of brown trout (Salmo trutta) reared in fresh water and sea water to freshwater rainbow trout (Oncorhynchus mykiss): II. Phosphorus balance

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 °C under the same conditions before transferring brown trout to sea water, in order to compare phosphorus utilisation in both species. Apparent phosphorus availability, orthophosphate excretion and phosphorus accretion in the fish were directly determined. Thus, actual phosphorus mass balance was built. Rainbow trout raised in fresh water had a higher phosphorus retention coefficient (maximum 50 %) than brown trout reared in fresh water (maximum 45 %). Transferring brown trout to sea water induced a reduction in phosphorus retention (maximum 39 %). Orthophosphate excretion, ranging 7–20 mg phosphorus per kg wet weight per day, represented 10–20 % of ingested phosphorus. Phosphorus availability was lower in brown trout raised in sea water (65 %) than brown trout raised in fresh water (76 %). Phosphorus balance measurements showed that 90 to 98 % of phosphorus flow could be accounted for.