Quote:
Originally Posted by Tripod1404
Many freshwater discus develop cataract like symptoms with age. It cause them to miss food. Maybe it might be similar to that
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With discus the cause of cataracts is pretty clear: in the wild they live in well shaded forest rivers. On top of that the water you find them in has the color of tea. So their eyes are used/adapted to twilight with little to no UV component.
If you put fish like those in clear water under bright lights and possibly even a significant UV component, you are bound to damage their eyes. Cataracts are pretty much predictable in that case.
But the eyes of tropical reef fish are generally adapted to relatively intense light with a significant UV component. Some shallow water fish actually have UV reflecting corneas to protect their eyes from things like cataracts.
Fish that only live in greater depths may however have problems with intense light and especially with UV.
The described cases however don't seem to be from cataracts as in that case the fish could still distinguish between light and dark and possibly even see shadowy images.
Also, cataracts can be easily diagnosed with a visual inspection of the fish's eyes.
Flukes covering the eyes would have a similar effect as cataracts - the fish would see everything very blurry, but could still see shadows and distinguish light from dark.
These cases rather seem to be caused by damage to the retina or the optic nerve.
In most cases once the damage is done it can't be reverted.
Causes may be chemical agents, bacterial infections or even parasites. If both eyes are affected, chemical or bacterial infections are the most likely culprits.
Another option would be damage to the visual cortex. Again, chemicals, bacteria or a tumor would be the most likely culprits.
Most observed cases of total blindness are likely caused by chemicals, especially if encountered soon after acquiring the fish. Either use of cyanide during capture or chemical treatments (overdose or combining incompatible meds) against diseases.
Other suspects may be excessive levels of nitrates, phosphates and organic pollutants. This could be the case if a fish goes blind after several years in the tank. Though these days nitrate and phosphate levels that could be harmful to fish should be rare and confined to fish only systems.
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