The biggest problem with housing them with tropicals is the temperature. Rock bass do best in cool water. When keeping fish like rock bass in warmer tanks, they tend to expire relatively quickly. The shallows where you caught the fish may be warm this time of year, but there is thermal refuge that the fish can return to just a few inches deeper. Plus think about how cold that water is in the fall, winter and spring. I would suggest you keep this guy in a separate tank.
Another issue is feeding them. They tend to be a pick pickier than their Lepomis sunfish cousins. Try feeding high protein, meaty foods (slivers of fish, earthworms, market shrimp). If you can get it to eat this, maybe you can start training it on a high quality pellet (but sometimes that never happens). I kept one from the time it was 2'' til it was nearly 3''. The problem was that they are very shy and could not compete for food with the other tankmates (redbreast sunfish and spotfin shiners). Eventually it never left cover, and the redbreast killed him when it reached sexual maturity and started defending a nest.
So, make sure it stays cool, and can get enough food to eat. Also, consider the fish's higher metabolism in warm water - it will need to eat a ton in order to not wither away.
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