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Old 08-29-2011, 01:29 AM   #1
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Question If a tank is placed next to a wall, with very dim light, will the fish go blind?

I have a freshwater tank with just 1 large common goldfish.

The tank is placed next to the wall, where there is little light. The light level is about the same as a bedroom with the windows covered with a medium thickness of curtain. It still has light, but somewhat dim.

I've noticed that my fish wasn't able to spot his fish food as accurately as before it was little. I always drop his fish food at the corner of the tank, but my fish would spaz around, gulping air at the center of the tank surface.

After a while, it would realize where the fish food is located, and start eating. It has been like this for about a year.

I'm starting to notice that its eyes are getting black. It doesn't have any diseases or anything blocking its sight, just that I can now see its skull and eye socket very well. By black, I meant that the eyes are very transparent. If I reflect the dim light from the curtains with a mirror, I can see a sliver of white at the back of its eyes. I'm pretty sure it's the skull, because the texture of the white is crispy-like.

1. Does the brightness of the room affect how the fish goes blind?
2. Will my fish start going blind?
3. Is it normal for a fish to have very black eyes when it is living in a dim-lit room for a long time?

Thanks in advance.
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Old 08-29-2011, 01:38 AM   #2
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I don't think a fish would go blind because of the dim lighting. The pupils are probably dilated because of the dim light, kind of like how a humans pupil gets large in the dark as well.
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Old 08-29-2011, 01:48 AM   #3
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I don't think a fish would go blind because of the dim lighting. The pupils are probably dilated because of the dim light, kind of like how a humans pupil gets large in the dark as well.
Fish eyes don't work like that (except a few species like the silky shark). They have a fixed pupil size because their irises are rigid. They adjust the position of the photoreceptors inside their eye to compensate for light changes. This process can take up to twenty minutes. Thats why some fish hide when you turn on the aquarium light. Your fishy is capable of adjusting to the dim light, so is he having vision issues, it is probably a degenerative condition or some such thing. I have seen this happen in some goldfish before.
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Old 08-29-2011, 01:52 AM   #4
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i had no idea, was just a guess, thanks for the correction
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Old 08-29-2011, 01:53 AM   #5
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i had no idea, was just a guess, thanks for the correction
No problem. I learned that in Natural History of Vertebrates class in college. It makes me feel good whenever I actually remember something from a class! Lol,
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Old 08-29-2011, 11:45 PM   #6
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What if constant rapid light changes were to occur near the fish, like a tank lamp flickering on and off?

I found an old fish tank lamp with broken contacts and broken plug, and thought I should try using it temporarily.
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Old 08-30-2011, 04:09 AM   #7
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What if constant rapid light changes were to occur near the fish, like a tank lamp flickering on and off?

I found an old fish tank lamp with broken contacts and broken plug, and thought I should try using it temporarily.
That would probably be somewhat stressful to the fish, so I would use floating plants to shield the fish from from the light. If it does not seen to bother them, then don't worry about it.
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Old 08-31-2011, 09:24 AM   #8
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Thanks for everyone's help.
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Old 09-20-2011, 11:29 AM   #9
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I guess someone already answered, but most fish only go blind due to disease or trauma.

Now, if the light is very low, it is important that you acclimate him to brighter light if you ever get a light or move him. Sudden prolonged brightness may cause stress that can lead to disease.
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