Not aggressive at all, they're schooling fish that travel in groups of several hundred in the wild. Gourami's would be fine as long as they aren't spawning, guppies or other small fish would likely be eaten. Tank needs to be tightly covered, they will jump out through any available opening. Not fond of current, really prefer little water movement and floating plants for cover. They will spawn in aquariums, but the fry are pretty well impossible to feed/raise. I've never heard of anyone doing it successfully.
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