J. Personleruyet et al., TOXICITY OF AMMONIA TO TURBOT JUVENILES - I - EFFECTS OIL SURVIVAL, GROWTH AND FOOD UTILIZATION, Aquatic living resources, 10(5), 1997, pp. 307-314
Long-term effects of constant exogenous ammonia concentrations were in
vestigated in two different batches of turbot juveniles (53 and 73 g)
under controlled environmental and feeding conditions. Over the 84-day
experiments, ambient un-ionized ammonia (UIA-N, NH3) concentrations w
ere steady (coefficient of variation, 12-16 %) and water pH range was
7.88-7.99. Survival was maximum up to 0.33 mg.l(-1) UIA-N and at 0.73,
50 % mortalities were observed on day 52 (73 g) or day 77 (53 g). No-
growth concentration was 0.73 mg.l(-1) UIA-N in the two groups and the
84-day lowest-observable-effect concentration range 0.14-0.33 mg.l(-1
). In the most tolerant group (53 g), the 84-day no-observable-effect
concentration was 0.14 mg.l(-1) UIA-N. The estimated 28-day efficient
concentration that gave 50 % of the specific growth rate of controls r
anged from 0.60 to 0.75 mg.l(-1) UIA-N. Specific growth rate to ambien
t ammonia concentration patterns were different in the two groups for
the lowest concentrations (0.14-0.34) and similar to food intake to am
monia pattern. Food efficiency was negatively correlated to ambient am
monia concentration, with major changes in food conversion ratio, and
protein utilisation observed above 0.33-0.70 mg.l(-1) UIA-N. The main
change in body composition was an increase in water content in all amm
onia-exposed fish. A significant increase in urea-N excretion rate was
also observed over 0.33 mg.l(-1) UIA-N. Thresholds for growth were af
fected by exposure duration. Turbot juveniles growth capacity may be d
epressed by usual ambient ammonia concentrations under intensive farmi
ng conditions.