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8. Eyes are cloudy.

 
Other than the gills, the eyes are the most vulnerable areas on a fish.  They often show the first signs of stress and becoming cloudy is very common.  Cloudy eyes can range from a slight opaqueness all the way to the gruesome sight you see in the photo.  The fish in the photo is suffering from a severe fungal infection brought on by poor water quality and damage to the eyes. 

In this photo fungus is the cause of the cloudiness but a cloudy eye does not indicate fungus.  A slight scratch or scrape on a fish's eye can cause inflammation and cloudiness.  Generally minor cloudiness will clear up on its own but as always: Maintain your tanks!  Get off the computer and do a water change now.  If you haven't done a scraping of the fish's eye and diagnosed the problem under a microscope, a water change is needed now!  Achieving good water quality can only help the fish's natural healing process. 

Whenever cloudiness is seen, inspect the fish for parasites and check water parameters.  Low PH and high Ammonia should be suspect.