Arowana fish when kept in an empty glass aquarium are sometimes prone to droopeye syndrome.
Droopeye in an arowana is when the fishes eyeball protrude slightly and tilt downwards. This can happen in both eyes or only in one eye with the other remaining normal. Many experts disagree on the exact causes of this problem but the solution to the problem remains the same.
It is hard to point to one exact issue that leads to droopeye syndrome or the reason why an arowana would develop a drooping eye. In the wild and in an aquarium the arowana is a natural surface swimmer, which means that everything is going to be below him. So here I will try and point out some simple steps to minimize your arowana developing droopeye.
Tank Reflection
Arowana fish are generally kept in an empty aquarium for ease of cleaning and maintenance. Since an aquariums surface is flat and polished then reflections will be seen within the tank. Since an arowana is a natural surface swimmer he will be consistently watching whatever moves below him.
If he is consistently seeing his reflection on the bottom of the tank then his eyes will be drawn to it automatically. If the arowana is always looking down and putting constant strain on his eyes then droopeye may develop.
A solution to this problem is to place a small layer of gravel on the bottom of your aquarium tank to stop the reflection. This will stop the fish looking at the reflection and hopefully help the fish to concentrate his eyes on the top of the tank.
Floats
If your arowana starts to show the early signs of developing droopeye then try and deal with it straight away. The main aim is to try and stop your arowana looking down and making the problem worse. One way that has been tried with varying success is floating one or two ping pong balls on the surface of the water. The ping pong balls will attract the arowanas attention and keep the fish looking up. This is one cheap and simple step you might want to try first.
Tank Position
When you have your tank set up make sure the tank is not to high. If the tank is to high then the arowana within the tank will be constantly looking down at objects or passing people. Have your tank placed at a nice middle level so the fish will be looking up a lot more than down. Again if you notice any signs of droopeye appearing another tip would be to lift your tank onto the floor so that the fish has to look up.
If your tank is to big to lift then you could try covering the outside of your tank with something dark so that the arowana cannot see out. This will mean that the arowana will have to look up.
Here I have shown you the simple, quick and cheap steps involved with trying to deal with droopeye in your arowana. Many experts differ in the causes and cures for this syndrome but have used the methods above with some degree of success.