Histopathology and the pathogenesis of embolism (gas bubble disease) in rainbow trout (Salmo gairdneri).

Rainbow trout (Salmo gairdneri) affected with gas bubble disease (GBD) were examined histologically to determine the pathogenesis of the early stages of gas emboli formation. Lesions preserved by a rapid fixation method were located in tissues associated with acid-secreting glands or with high metabolic requirements. Following the development of small gas emboli formed in the retinal chorio-capillaries, a progressive development of unilateral exophthalmia was detected. A lesion found in every treated moribund fish but never in controls was gas displacement of the blood from the afferent arteriole within the gill filaments. The exposure of fish to well water containing graded levels of atmospheric gases from 114 to 118% nitrogen and 103 to 110% oxygen saturation resulted in high mortality. However, fish held in nitrogen varying between 103 and 117% and oxygen from 50 to 94% saturation experienced insignificant mortality. We suggest that hatchery oxygen levels should be maintained below 100% if nitrogen sup...