Bright aquarium lighting is sometimes implicated in causing blindness, especially in lionfish (Pterois spp.)

Answer: Thanks for your question, Sean! In his book The Salt Smart Guide to Preventing, Diagnosing, and Treating Diseases of Marine Fishes, Jay Hemdal addresses the issue of blindness in fish—specifically the subtle symptomatic differences between a fish that is going blind and one that is actually ill to the point of becoming moribund. Here is that particular excerpt from his book, which I think will answer your question better than I can: Blindness A very common symptom reported by home aquarists is that one of their fish has become blind. This, more often than not, is a result of a fish becoming ill to the point that it is moribund (close to death) and is not just blind. Basically, a fish that bumps around the aquarium, runs into the tank sides, and ignores food may not be blind at all; it may just be dying MORE