Those fish are not all from the same places. Tiger Barbs are from Indonesia/Borneo the others are Australia & Central or South American. (forgotten which)
The barbs will become a snack for the Arrowana, no question, & probably the Ray to.
I would not have a Ray & an Arrowana in the same tank. The ray needs lots of open bottom space & the Arrowana likes a densley planted tank. You would have problems trying to decorate the tank to the liking of them both.
Not sure how Severums will get along with the Arowana when it gets older. Sevs are pretty mild mannered & spend alot of thier time inthe same region of the tank as the Arowana would. They would be rather intimidated by it I think. Perhaps you would be better off skipping on the Ray & Severums & go with something like a Geophagus species that is peacefull but will mostly stick to the substrate.
Seeing as the Arowana will take up all of the available swimming space, I don't think it will be real happy if only the back & sides were planted. It's going to want to get behind the plants so that it doesn't feel so exposed.
There are plenty of shoaling fish that are not silver but I think most of them would become a midnight snack for the Arowana when it gets a little bigger. Perhaps Madagascan Rainbow (Bedotia Geayi) would work. They get to around 6" but are long & slender (meaning easy to swallow). Red Rainbow (Glossolepis Inisus) would be another candidate at about 4". With some luck the Rainbows would be fast enough to get out of the way of the Arowana.
Not a good idea to put something that might represent food in with the Arowana though IMO. When the Arowana makes surprise attacks it could injure itself given that the tank is really too small for it. Could even damage the tank when it gets really big.
Nutter you are like a human encylcopedia. I am amazed at how much you know. I will think about the rainbows and continue my search for the perfect non-silver shoalers. Again once the arowana outgrows the tank I will give it a new home as long as that home is better than the one it came from. I am also thinking of a jardini because it will be more suitable for a 180 gallon. But please keep the feedback coming
Jardini are very very cool fish. 180gal woud be what I would consider minimum for them. 300gal is much more appropriate to thier potential size of around 30" but they usually stay under 24" in the home aquarium. Those guys are definite predators & shouldn't be housed with any fish under 10".
I know your intending the tank upgrade. I only mentioned the tank size because of the potential for injury during the ambush attacks.
Well I do not exactly intend on upgradign the tank I can not afford much more. But once the fish outgrows the tank I will look to give or sell it to someone who has a larger tank then I. As long as i can find someone with a 300-400gal willing to except such a large fish.
If I do happen to house a jardini I will look for fish more like a alligator gar or tiger shovelnose cat.
Depends on which one your thinking of. There are an awful lot of Syno species from all sort of water. Can you narrow down what sort your thinking of or at least give us your water parameters (PH & GH) so that we can make suggestions?