BLOOD-CHEMISTRY AND ACID-BASE-BALANCE IN RAINBOW-TROUT ONCORHYNCHUS-MYKISS WITH EXPERIMENTALLY-INDUCED ACUTE BACTERIAL GILL DISEASE

Rainbow trout were experimentally infected with the causative agent of bacterial gill disease (BGD) (Flavobacterium branchiophilum) via bath challenge. All fish were cannulated with dorsal aortic catheters, had nasogastric tubes sutured in place for feeding, and were maintained i ndividually, in plexiglass boxes with a flow-through water system. Fis h were either fed, or unfed during the trial. Acute changes in blood g as, serum biochemistry and clinical parameters were monitored. By 24h post-challenge, BGD-infected trout that had been fed had significant h ypoxemia, hypercapnia, increased blood ammonia, hypoosmolality, hypona tremia, hypochloremia, and increased cough and respiratory rates when compared to control levels. Unfed BGD-infected trout had similar, but less severe blood gas and clinical changes, and no electrolyte disturb ances. The BGD-induced hypoxemia is likely exacerbated by increased ox ygen demands brought on by feeding. It is not known what association f eeding has with the development of low serum ion levels in BGD-infecte d trout. This is the first study to report the use of fed fish, as opp osed to unfed or starved trout, in obtaining blood chemistry values fr om indisturbed and cannulated animals.