Pathology of ocular lesions associated with gas supersaturation in white seabass

Cultured juvenile white seabass Atractoscion nobilis (WSB) can suffer from intraocular emphysemas and exophthalmia in the hatchery environment. To identify the cause, two size-groups of WSB were exposed to five gas saturation levels, ranging from 98% to 122% total gas pressure (TGP), over a 96-h exposure period in 18 degrees C and 23 degrees C seawater. Histological examination revealed that the gross and subgross lesions associated with gas supersaturation included corneal and orbital emphysema, along with subretinal, optic nerve, and iridial hemorrhage. Corneal emphysema was the most prominent gross lesion, with the severity and prevalence increasing between size-groups and water temperatures as TGP increased. Following the same pattern was orbital emphysema, which affected more than 93% of the fish examined and caused hemorrhage in the subretinal space, around the optic nerve, in the iris, or a combination thereof. Iridial hemorrhage occurred in 91% of the fish examined and decreased significantly with fish size. The prevalence and severity of hemorrhage in the subretinal space increased significantly with TGP and fish size but not with temperature. Optic nerve hemorrhage was absent in small fish exposed at 18 degrees C but increased significantly with temperature and fish size. The reverse was true for the large fish.