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Studies were conducted to determine the potential pathogenicity of Edwardsiella ictaluri to economically important nonictalurid fishes in California, USA. White sturgeon Ac~penser transmontanus, striped bass Morone saxatilis, and chinook salmon Oncorhynchus tshawytscha were immersionchallenged in parallel with channel catfish Ictalurus punctatus. During a 14 d period, chlnook salmon and channel catfish succumbed to ~nfechons with E, ictalun but the other species did not. An immersion exposure to 4.0 and 7.9 X 10' cfu rill-' of E. ictalun for 30 S resulted in a 92 and 48 % mortality among chinook salmon and rainbow trout 0 . mykiss, respectively. A Gram-negahve septicemia occurred m infected fishes, and pure cultures of E. ictaluri were recovered from dead and surviving fish. There was a moderate to severe necrosis of the Liver and kidney in both salmonids and channel catfish. Intracellular bacteria occurred within mononuclear Inflammatory cells and hepatocytes. These results suggest that E. ictaluri is a potential pathogen of salmonid fishes.

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Tetracycline (TC) and oxytetracycline (OTC) caused a dose‐dependent suppression of the chemiluminescence (CL) emitted by phagocytes from the kidney of rainbow trout, Salmo gairdneri, using zymosan or latex beads as the stimulus. Compared to the control response without antibiotics, partial but significant suppression was found after exposing the cells to OTC concentrations of 0.1–50.0 μg ml−1. Cells exposed to 100 or 500 μg ml−1 OTC showed CL responses below the base levels elicited by control cells. Comparable results were obtained with cells exposed to TC and stimulated by the same stimuli. The kinetics of the CL response and the suppressive effects of the antibiotics were similar in cells from individual fish but the magnitude of responses varied. No acclimation occurred following extended exposure to the drugs.