Abstract

Reports of cataracts in captive fish are plentiful, particularly in trout and salmon. Formation of cataracts has been linked to nutritional deficiencies^11,10,4,17, rapid growth rates^2,3, genetic inheritance¹⁵, toxins^8,9, infectious agents, osmotic stress, and excessive exposure to ultraviolet (UV) radiation^5,6,16,19. Retinal degeneration, in contrast, has been documented infrequently and has been associated with genetically manipulated transgenic zebrafish^7,12 and celestial goldfish^13,14, and with diabetes mellitus in carp.¹⁸ Eight of 18 wild-caught juvenile Pollack (Pollachius virens) were placed on display in a brightly lit tank at the National Marine Fisheries Service (NMFS) Aquarium in Woods Hole, MA, and 10 were shipped to the New England Aquarium (NEA) in Boston, MA. Six of the 10 pollack received by NEA were relocated to a dimly lit display tank, whereas 4 were placed in a brightly lit, basin-like tank, in a Puffin display. Within 4 months, 5 of 6 pollack in the dimly lit tank developed cataracts diagnosed by ophthalmoscopic examination. Affected pollack grew increasingly unable to locate food, became emaciated, and were euthanized 5 months after diagnosis. No gross lesions were identified in the coelomic viscera at necropsy examination, and globes were immersion-fixed in Bouin's solution for routine paraffin embedding and histopathologic examination. Subcapsular, cortical cataracts were found in 4 of 5 pollack, and were bilateral in 3 and unilateral in 1 pollack. Marked to severe retinal degeneration and atrophy was evident in 5 of these 5 pollack, the most severe degeneration being central rather than peripheral. None of the other 12 pollack from the original cohort of 18 developed cataracts clinically evident by ophthalmoscopic examination ante-mortem. However, upon histologic examination, 4 of 5 pollack from the NMFS facility had mild, focal, subcapsular cataracts, 3 unilateral and 1 bilateral, and 1 had retinal degeneration comparable to that of the pollack from NEA. In comparison, no microscopic lenticular or retinal lesions were identified in 5 wild-caught, adult pollack acquired from Connecticut fisherman and examined in the manner previously described. To our knowledge, this is the first documentation of the combination of cataract and retinal degeneration in a species of the family Gadidae. Differences in environmental and husbandry factors exist between the two NEA tanks and the two aquaria to provide clues as to the causative agent(s). Current investigations into the etiology are focused on determining variations in UV light exposure and nutrition between the three aquarium settings.

Acknowledgements

The authors acknowledge Tania Taranovski, Brandon Schmidt, and volunteers of NEA for their care of pollack, for providing answers regarding the husbandry conditions, and for assisting in medical examinations, euthanasia and necropsies of affected fish. We are grateful to Kevin Dunn from the National Marine Fisheries Aquarium for donating 5 pollack for this study and for supplying answers as to the husbandry conditions at the NMFS.

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