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Ammonia detoxification and localization of urea cycle enzyme activity in embryos of the rainbow trout (Oncorhynchus mykiss) in relation to early tolerance to high environmental ammonia levels

Shelby Louise Steele, Terry David Chadwick and Patricia Anne Wright^*

Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1

View larger version (21K): [in a new window]   Fig. 1. Activities of glutamine synthetase (GSase), ornithine transcarbamoylase (OTCase), arginase and carbamoyl phosphate synthetases (CPSases) II and III in the yolk sac, embryonic body and liver fractions of rainbow trout just after hatching (38 days post-fertilization). Values are means + S.E.M. of five measurements (30–50 individuals were pooled for each measurement). BLD, below levels of detection.

View larger version (17K): [in a new window]   Fig. 2. Mean percentage cumulative hatch (means ± S.E.M.) of rainbow trout embryos exposed either acutely (2h) to 10mmoll-1 NH4Cl or chronically (4 days) to 0.2mmoll-1 NH4Cl (N=6).

View larger version (17K): [in a new window]   Fig. 3. Rates of ammonia (A) and urea (B) excretion (µmolNg-1h-1) of rainbow trout embryos at several times following treatment with 10mmoll-1 NH4Cl (means ± S.E.M., N=6). An asterisk indicates a significant difference from controls.

View larger version (17K): [in a new window]   Fig. 4. Rates of ammonia (A) and urea (B) excretion (µmolNg-1h-1) of rainbow trout embryos over time during a 4 day treatment with 0.2mmoll-1 NH4Cl (means ± S.E.M., N=6). An asterisk indicates a significant difference from controls.

View larger version (21K): [in a new window]   Fig. 5. Ammonia (A) and urea (B) concentrations (µmolNg-1) in the yolk and embryonic tissues after either acute (2h) exposure to 10mmoll-1 NH4Cl or chronic (4 days) exposure to 0.2mmoll-1 NH4Cl (means + S.E.M., N=6). An asterisk indicates significant difference between control and treated animals; a double dagger indicates significant difference between yolk and embryo.