October 31st, 2016 — Last summer’s heat probably caused sunburned fish.
When several Pequest Hatchery broodstock rainbow trout had developed whitish skin lesions on the dorsal surface that were spreading to the body of the fish, the doctor was called.
Jan Lovy, a research scientist in fish pathology for the Division of Fish and Wildlife, reported four broodstock rainbows were euthanized and necropsied.
Bacteriology was done on the skin lesions and the kidneys of the fish, and no significant infectious pathogens occurred within the skin lesions.
Lovy is the chair of the Technical Standard Committee in the American Fisheries Society’s Fish Health Section, and knows about diagnostic methods on fish health, so he knows his stuff.
Bacteriology was negative for all fish examined, and his report states: “The skin lesions appeared to have been related to sunburn, caused by the fish hanging out near the water surface on sunny days.”
Shaded roofs over the trout raceways would prevent fish from developing sunburn in the future. Also, ospreys and other birds that eat trout would be prevented by roofs from eating hatchery trout.
Catfish, bottom feeders, have no sun problems. But they don’t jump. When rainbows are hooked, they frequently go airborne.