Salty Q&A: Is My Lionfish Going Blind?

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

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


I have a volitans lionfish that’s been in my 200-gallon tank for over two years, and lately it has begun to act like it can’t see. At feeding times, it makes an effort to grab food that’s drifting by but usually misses—like it can tell that food is in the water but can’t see it well enough to get it in its mouth. Is there a way to tell if this fish is actually going blind versus having some other health problem? – Submitted by Sean Myles


Thanks for your question, Sean! 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:


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.

A truly blind fish will behave as if it is night and may even show its nighttime coloration. The fish will swim very cautiously to avoid running into obstacles, and it will orient itself in the normal upright position. If food is added to the tank, it will attempt to seek it out, perhaps by moving its mouth along the bottom of the tank, snapping up any food that it may come in contact with.

It is important for the aquarist to be able to distinguish the subtle differences between these two problems, as a truly blind fish may live for many years given extra care, while a moribund fish will continue its health decline and soon die if the problem is not corrected.

Bright aquarium lighting is sometimes implicated in causing blindness, especially in lionfish (Pterois spp.). Only anecdotal reports of this are available, and since aquarium lighting is many times less intense than on tropical reefs, cause and effect cannot be linked. Feeding freshwater fish to marine predators (again, often lionfish) is also reported by home aquarists to cause blindness. In these cases, it is most likely that the predator has developed fatty liver disease and the fish has become moribund from that.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. MO poor foods and feeding are a cause of blindness in fish as can also be the case in humans. In particular gamma irradiating food has an adverse affect on vitamins in the food and in particular vitamins A and B2. A lack of vitamins A and B2 is known to be a cause of blindness.
    Quote “Riboflavin (vitamin B2) and Vitamin A are both important for the continued eye health and proper vision in fishes.
    I never feed gamma irradiated foods to my fish but then I make much of my own foods anyway.

  2. mauigold808 says

    Chronic high Nitrates can also cause blindness in fish

  3. Puffers, lionfish, squirrelfish, bangai cardinals and all fish with large eyes often go blind in a reef tank. Of course as Jay said it could be the result of illness but another common cause is lighting. Fish in the sea are exposed to much brighter lighting than our tanks but those fish spend a large amount of time under overhangs, in caves or on vacation. If you do any diving you will notice all the squirrelfish are in caves. Many of our tanks just don’t provide large enough spaces for fish to get out of the “sun”. The large eyes on those fish allow them to see better in darkness but in a brightly lit aquarium it is a detriment. I have had lionfish, Big eyes, squirrelfish and puffers go completely blind but it was never permanent and putting the fish in a dimly lit tank for a week or two always cured it to where the fish had 20/20 vision again and could read a newspaper or racing form.

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