J. Person-Le Ruyet

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.

Chronic ammonia toxicity in juvenile turbot (Scophthalmus maximus)

Abstract Chronic effects of ammonia were studied in three batches of turbot ( Scophthalmus maximus ) juveniles (14, 23 and 104 g) exposed for 4–6 weeks to constant ammonium chloride solutions. Under the environmental conditions used (16.5–17.5 °C, pH 7.92–8.03, salinity 34.5 ppt, over 80% oxygen saturation), no mortalities occurred up to 0.4 mg unionised ammonia (UIA-N) l −1 , i.e. 10 mg total ammonia nitrogen (TAN) l −1 . Estimated 28-day LC 50 s averaged 0.95 mg UIA-N l −1 and growth was stopped from 0.8 mg UIA-N l −1 . In 14 and 23 g turbot, LOEC (lowest-observable-effect concentration) values for growth were 0.41 and 0.21 mg UIA-N l −1 , respectively, compared with 0.10 mg UIA-N l −1 in 104 g turbot. In 14 g fish, the most tolerant group in terms of growth, NOEC (no-observable-effect concentration) and MATC (maximum-acceptable-toxic-concentration) values were 0.18 and 0.30 mg UIA-N l −1 , respectively. Reduced growth rate was due to a decrease in food intake, not to poorer food utilisation. The food conversion ratio was 0.9 and PER (protein efficiency ratio) and PUC (protein utilisation coefficient) averaged 2.5 and 45%, respectively. No significant changes in body composition were observed up to 0.4–0.5 mg UIA-N l −1 . In adapted small turbot, no major physiological disturbances were observed up to 0.4–0.5 mg UIA-N l −1 , while large turbot were more sensitive to ammonia. Major changes were observed in blood plasma TAN contents which were positively correlated with ambient ammonia concentrations. Chronic lethal levels and chronic adaptation levels of TAN were respectively about 20 and 13–15 mg l −1 plasma. Significant increases in plasma urea-N contents and urea-N daily excretion rates were only observed for the highest ammonia concentrations tested.

Comparative acute ammonia toxicity in marine fish and plasma ammonia response

Abstract Using a continuous-flow method a total of 14 acute toxicity bioassays were conducted using seabass ( Dicentrarchus labrax ), seabream ( Spams aurata ) and turbot ( Scophthalmus maximus ) juveniles weighing from 6 to 163 g (wet weight). Median LC50s of un-ionized ammonia-nitrogen (UIA-N) and median LT50s (plus their confidence intervals) were calculated for 6, 12, 24, 48 and 96-h exposures for each trial. Under optimal environmental conditions (17–18 °C, 34%. S, 8.15 pH and oxygen over 75% saturation), median 96-h LC50s averaged 1.7 mg 1 −1 UIA-N (40 mg 1 −1 TAN, total ammonia nitrogen) in seabass compared with 2.5–2.6 mg 1 −1 UIA-N (57–59 mg 1 −1 TAN) in seabream and turbot. Median LC50s did not change significantly from 24 to 96-h exposure and were not related to fish size. Significant variations in fish sensitivity were observed from one group to another and seabass juveniles appeared to be more susceptible to ammonia than seabream and turbot. In all species, mortality occurred over a relatively narrow range of ammonia concentrations. Lethal threshold concentrations (LTC) were estimated to be over 90% of 96-h LC50s. In starved fish, blood plasma levels of ammonia, which were positively correlated with ambient ammonia, can be used to estimate the extent of ammonia toxicity. The same increase in plasma TAN vs. ambient ammonia level was observed in seabass, seabream and turbot. A mortality of 50% was observed after a 4-day exposure when the increase in TAN was 4 times the initial level in seabass and more than 10 times the normal level in seabream and turbot. These results show, for the first time, that seabass unlike seabream and turbot have lower thresholds of physiological disturbances, which explains why they are more sensitive to ammonia.

Effects of O2 supersaturation on metabolism and growth in juvenile turbot (Scophthalmus maximus L.)

Abstract Effects of O2 supersaturation on metabolism and growth were studied in juvenile turbot (Scophthalmus maximus L.). When fish were reared for 30 days in water containing O2 at 147% or 223% air saturation, there were no significant differences in food intake, growth, food conversion or protein utilization compared to fish exposed to normoxia (100% air saturation in water outlet). Exposure to hyperoxia resulted in increased body fat deposition. Daily rates of O2 consumption of resting fish were not affected by O2-concentrations, and there were no significant differences in rates of nitrogenous excretion among fish exposed to the different O2-concentrations. Turbot tolerated severe hyperoxia, 350% air saturation, for 10 days. There were changes in acid–base balance that compensated for the respiratory acidosis resulting from O2 supersaturation. Blood pH was regulated within 24 h (it averaged 7.69 over the 30-day experiment) by significant increases in plasma CO2 content and pCO2. Plasma CO2 was dose dependent averaging 11.3 and 18.9 mmol l−l under 147% and 224% O2 saturation, respectively, compared to 6.7 mmol l−l under normoxia. Over the 30-day experiment, the only change in hydromineral balance was a slight, but non-significant decrease in plasma chloride content in fish exposed to hyperoxia (137 mmol l−l compared to 139 under normoxia). There were no changes in haematocrit, haemoglobin and red blood cell counts (they averaged 18.3%, 3.7 g dl−1 and 1.37×106 mm−3, respectively) and no signs of stress (plasma cortisol averaged 3.8 ng ml−1) related to exposure to O2-supersaturation for 30 days.

Techniques d'elevage intensif de la daurade doree (sparus aurata (L.)) de la naissance a l'age de deux mois☆

Abstract The larvae were reared in cylindro-conical tanks from hatching to 25 days old and transferred into square flat tanks after this age. The larvae were fed on living prey up to 40 days old and then weaned onto dry pellets. A total of 80,000 just-hatched larvae was used in the experiments and the survival rate was 11% up to 2 months old (weaned larvae). The best batch of larvae had a 65% survival rate from hatching to 25 days old. Two thousand eight hundred and sixty fingerlings, 97% of the number produced this year, were obtained with 8% survival from hatching up to 2 months old. The general rearing technique, the feeding scheme and the daily amounts of food used are described.

Elevage larvaire d'Artemia salina (Branchiopode) sur nourriture inerte: Spirulina maxima (Cyanophycee)

Abstract A technique for the intensive rearing of Artemia salina larvae (Branchiopoda) of 1 – 4 mm using the blue-green algae, Spirulina maxima (Cyanophycea) in dry powder form is described. Experimentation was carried out in a small volume (20 l) and techniques were simplified whenever possible to enable minimal handling (i.e. water is not renewed). The system is therefore easily applicable to medium and large volumes. The production requirements of Artemia salina for larval aquaculture at Centre Oceanologique de Bretagne have been fulfilled by this technique since 1974 in 450-l volumes. Growth and survival rates have been satisfactory to date. Up to a certain threshold and within a given age group, the amount of food introduced influences mean population size. Under optimal conditions it is possible to rear larvae of 1 mm in 2 days, 2 mm in 4 days and 3.75 mm in 6 days. The minimal food supplies required to obtain these figures are respectively 600 mg, 1 800 mg and 4 300 mg of Spirulina powder for 10 000 larvae at the ages of 2, 4 and 6 days. These rapid growth rates are achieved by overfeeding the larvae, which results in a reduction in the size of the installations and in time demanded for culture maintenance. The use of an optimal feeding regime gives a growth rate very close to the maximum and diminishes production costs only slightly. Consequently, an optimal larval concentration per unit volume is the most economically feasible choice for a production unit. The maximum larval concentration which gave good growth and survival rates was established for an average food quantity (3 200 mg/10 000 larvae). Larval densities may reach 13 to 14 2-day-old larvae (1 mm), five 4-day-old larvae (2 mm) and two 6-day-old larvae (3.75 mm) per ml of water. To regulate the concentration of Artemia, fixed volumes of the culture are removed regularly, thus considerably increasing the production of a given tank. The weekly production of a 450-l tank is approximately 75 g of dry matter.