Are 2 Oscars and 2 Jack Dempseys compatible in a 75-gallon tank?

A 55 gallon tank is truly not large enough for an Oscar. Usually they are housed singly or in a mated pair. A single adult Oscar should have around a 75 gallon tank MINIMUM and a pair needs 100G or larger. Here's a bit more info on Oscars https://www.petcoach.co/article/oscar/

Probably not, for a few reasons. The first is tank size. Unless you have a large tank, upwards of 150+ gallons, 2 Oscars can overwhelm a smaller tank and filter with their bio load (wastes). Ideally, you want at least 55 gallons per Oscar. Another reason against it would be that if you end up with 2 males, it is likely they will be fighting constantly until one is injured or worse. Lastly, the long fins on the fan tail will invite nipping which will cause injury and may lead to infection.

Thanks for reaching out. Oscars are fairly aggressive and will try to eat each other, depending on their size. Be prepared to separate if needed and monitor interactions. Keep them well fed and provide plenty of hiding locations. Good luck.

All these fish can grow quite large. The loach would be the "smallest" at about 6 to 8 inches when full grown. The Oscars can reach lengths of 18 inches and the Texas cichlid and sharks can reach a foot in length. All these fish will require much larger tanks than the ones you have now. The three Oscars alone would do best in a 125 gallon aquarium MINIMUM. The others may thrive in 55 to 75 gallon tanks. To leave them in small tanks will cause stress, aggression and likely infection.

As long as thee oscars are small there will be no problem, however they grow very fast and they will eat all your other fish except the gouramis. So yes, you will need a separate tank for them and preferably at least a 40 gallon tank. The same is true for the parrots, another cichlid species.

That would depend on the size of your tank and the size of the oscars. Arowanas need a lot of space usually. I have seen them successfully being kept with arowanas before, but the oscars must be at least the same size of their mouth, not smaller. Unfortunately there are not fixed ruled and the only way would be to try them out together. Hope this answer was helpful, but please do not hesitate to contact us again on the forum or by requesting a consultation if you have any more questions or to discuss it any further.

Thank you for using Petco Pet Education Center, formerly Petcoach! It looks like the tank provides enough room for Speedy and Explorer to swim comfortably. Keep an eye on them, and move them into a larger tank if they get significantly larger or you notice signs of fighting or increasing ammonia levels in the tank.