Oscar Has Developed Cloudy Eyes
People often come on our forums asking why their fish have developed cloudy eyes, whether it be one, or both of them. Probably the most common cause of cloudy eyes in fish seems to be directly related to poor water quality. This could be prolonged exposure to high ammonia and nitrite, or keeping fish in water with a very high nitrate content. A very low pH can also be the cause of cloudy eyes. We wouldn't recommend letting your pH drop below 6.0 so it's always important to carry out a pH test on a regular basis and carry out water changes to maintain your pH level if you do find it dropping. The problem with keeping Oscars is they create an enormous amount of waste which in turn has a direct effect on your pH and will cause it to drop. Again, how quickly this happens depends on the pH level in your tap water. If like me your tap water has a pH level of 7.5 and an aquarium level of around 6.0 then regular 40% water changes stop the pH from dropping too low.
If poor water quality is not an issue then there are other things that may cause cloudy eyes in aquarium fish. Internal parasites such as flukes can also be the cause of cloudy eyes. You may not be aware that fish can develop cataracts. Unfortunately there is no known treatment for cataracts in fish, I doubt whether it would be feasible for a veterinary surgeon to carry out an operation to remove cataracts. A bacterial infection within the I can also be the cause of cloudiness, in this case a good quality antibiotic may help.
Fish need to the fed a healthy diet, an unhealthy diet may result in the fish suffering from a lack of vitamin A which again can affect the fish's eyes.
Finally, a fishes eye is extremely delicate so any damage caused by the fish either being attacked by another fish, or swimming into something in the tank could cause the eye to cloud over.
If you do notice that your fish start developing cloudy eyes then you must act quickly. Carry out increased water changes and if the cloudy eyes clear up quickly then it may have been down to your pH level. If increased water changes do not work then you will have to look at other forms of treatment.