| Abstrakt: |
Rainbow trout, Salmo gairdneri Richardson, were reared intensively in nine aerated static-water ponds. Dissolved oxygen concentrations were maintained above 5 mg/l and un-ionized ammonia (NH3) levels were monitored in all ponds. Fish were removed periodically and gill, liver and trunk kidney samples were removed for histological examination. Average NH3 concentrations did not exceed a previously reported chronically toxic level, but average daily maximum concentrations exceeded this level in all but two ponds. Gills exhibited lesions characteristic of those attributed to ammonia exposure in all ponds and fish with the most damaged gills had livers demonstrating reduced glycogen vacuolation. No histological changes were noted in kidney tissue. Because gills were damaged even though average NH3 levels were quite low, it is recommended that research in static water carefully consider the cyclical nature of NH3 concentrations. [ABSTRACT FROM AUTHOR] |
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