Gday all, ive got a Red Tiger Oscar thats hit bout 8inches long now and its been getting very territorial and has been making what looks like a nest, starting to get worried as it keeps headbutting the glass very hard

Cichlids are territorial, and will claim a territory (if they can) and probably make a nest there.

Maybe your oscar chose an awkward spot to build his territory?

What you could try to do, is to rearrange the things in your aquarium, take note of where he (or she) chose to build a nest now and see if you can encourage it to build a nest perhaps further away from the glass. It might be that it sees its own reflection in the glass and tries to chase off its reflection from its territory. -That said, maybe ensuring theres no reflection will work as well.

Hi

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At eight inches it is still a sub adult. It may be just venting extra energy. You should consider getting it a pair about the same size. They are very territorial by nature. A pair will clean some surface in the aquarium to lay their eggs. If you have any substrate in the aquarium then they will dig it up to create a shallow pit that may extend to the bottom of your tank. Check your water quality & check the fish eye for cloudiness. If it is clouded then it could be a disease & the reason why he keeps banging on the glass sides.

Oscars are strange fish. They will engage in all kinds of weird behaviors. They will scoop all the tank gravel from onside of the tank to the other. I walked into the room one day and found him laying on the bottom of the tank. I thought it was sick. Then another oscar owner said that they will do that when they are p****d off. Shure enough, about an hour later he was back to swimming around. We finally figured that for about an hour a day, the sun would shine through a window and onto his tank. He didn't like so he would swim to the bottom of his tank and stay. There till the sun moved off his tank.

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We closed the window shade, problem solved. So don't worry about your oscar. Just enjoy him.