NECROSIS OF TROUT RETINA (ONCORHYNCHUS-MYKISS) AFTER SUBLETHAL EXPOSURE TO NITRITE

Rainbow trout exposed to sublethal concentrations of nitrite accumulate this substance to different degrees. The result is a formation of methemoglobin in amounts ranging from 6 to 100% of total hemoglobin. In contrast to tolerant specimens (low nitrite accumulation), the eyes of most of the intolerant trout were severely affected. Alterations ranged from necroses of single retinal neurons to complete destruction of the retina. Since severe direct or hypoxic damages to other organs have not been observed, the striking reaction of the retina may be attributable to its high oxygen demand. The impaired function of the choroidal rete mirabile is believed to lead to a reduced oxygen supply or to acidification of the ocular fluids.