Can I adjoin my jack dempsey and tiger oscar together?

If you put one in the other's tank, the one that lived in the tank will become aggressive to protect "his" tank. However, if you get a new tank big enough for both, they should be ok as neither will have an established territory. If you want to put one fish in the others tank, it is best to completely rearrange everything int he tank, add some new plants and new decorations which will trick the fish that has lived in the tank into thinking he is in a new place.

The key is plenty of plants and decorations so if they do not want to look at one another, they have things to keep between them. Oscars and Jack Dempseys have long since been housed together and gotten along great. The Dempseys are the unfriendlier of the two, so your main job is keeping an eye on him.

You will never know till you try. Try it out, if they don't get along, at least you have the tanks to keep them separate.

FYI, an Oscar and a Jack Dempsey need a 75 gallon take to live healthily and happy.

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I keep and breed both. Minimum 90 gallons without any other tank mates. Tiger Oscars and Jack Dempseys are normally ok for about 3 years. The Oscar should roughly get to 12" within the first 12-15 months of it's life and will then continue to slowly grow anywhere from 14-18" The Jack Dempsey will only reach about 6" by the end of the first year, actually 4-6" is about the norm. It will grow pretty slowly up to about 3 years of age in the 10-12" range. You shouldn't have any problems until the Dempsey reaches full size and realizes that the Oscar is a slow and clumsy tank mate that can only bully things that fit in it's mouth. Then odds are that your Dempsey will kill your Oscar. But as you gave away your last cichlids, which any true fish keeper wouldn't do...you'll no doubt end up getting bored of these 2 and giving them away far before they reach even the juvenille stage. Sorry if the truth hurts.

If you took the host fish out and rearranged the decorations in the tank (redistributes the territory), then they should be fine. That is assuming your tank is big enough. Two big fish like that will probably require 120+ gallons in order to not kill each other.

I'm not sure about oscars, but with jacks you can lower the water temperature a little bit, and they will be less aggressive. You may want to look into whether this is a possibility for the first couple of weeks, while they get used to each other.

Oh, and don't get rid of the empty tank until you are sure this combination will work. That way, you can always move the bullied fish into the old tank.

Oscar And Jack Dempsey

probably not try to get a 100-120 gallon and put other cichlids with the other 2 so the aggression is suppressed

No way to know for sure.

It's possible to keep the two species together, but it's best if they have grown up together, and they are going to need plenty of space. If the two are still juveniles then it worth a try. If they are old, grumpy and set in their ways it's more risky.

Ian