Disorders of the eye in finfish

Abstract

As fish have been brought into confinement for display and culture, eye diseases have often caused difficulties, sometimes major. Types and possible etiological factors vary. All eyeball (orb) parts and attached organs and tissues (adnexa) are affected. Most common are exophthalmos (pop-eye), cataracts, keratopathy (several corneal lesions), various retinopathies, and uveitis (choroid and iris system lesions). Less frequent in cultured or feral fishes are: aphakia (no lens); choroid gland disease; cyclopia; edema of various tissues-including the lens; endophthalmos (sunken-eye); hyperemia of all parts; microphthalmos (small-eye); neoplasia of cornea, retina, and other parts; and others. These lesions may result from poor water quality, including gas imbalances (causing exophthalmos), toxicants (cataract, hyperemia, keratitis, and retinitis), low temperatures and osmotic imbalances (cataract); nutritional deficiencies (cataract, corneal, and retinal diseases); parasitemias (exophthalmos, cataract, keratitis, etc.); radiation damage (cataract, keratitis); trauma of careless handling; and injuries from unsafe culture systems. All conditions are exacerbated by stresses associated with culture, including overcrowding and aggressive behavior. Immunological deficiencies and genetic factors are also involved. In display aquaria, hatcheries, and nurseries, eye disease may not be fatal but often affects growth and is unsightly. Further, cataracts can indicate serious nutritional problems leading to other diseases. Exophthalmos, ocular hyperemia, cloudy corneas, cataracts, and granular and inflamed eye tissues may signal unfavorable water supply or parasitemia resulting from poor sanitation. Unthriftiness and deaths may result. Chances of survival or responsive behavior of released vision-impaired fish are markedly reduced and purposes of culture and release programs negated. Also, buyers, believing they reflect poor product quality, may reject animals with abnormal-appearing eyes. Whichever occurs, stock, biomass, time, and monetary losses can be significant. Eye diseases of fish, their possible causes, significance, and prevention or treatment, if any, are described and discussed.