One of the largest groups of fish available for the aquarium would have to be the Characins. The group includes many popular fish such as tetras, hatchetfish, and the red-bellied piranha, just to name a few. What makes the Characins such a unique group is that they have a special adaptation called “Weberian apparatus,” which connects the hearing organs and the swim bladder together. What this means is that the swim bladder will amplify sounds and provide the fish with an enhanced sense of hearing.
Characins are also very aware of changes that occur in their environments, what this means for Characins in the wild is that they are extremely good at making schools, finding food, and evading their predators. Because they have the weberian apparatus make sure that the tank doesn’t have something that vibrates to much touching it, this will stress the fish. So in other words it’s not recommend that you put the air pump on top of the tank, that is, if you have a glass canopy.
Almost all of the Characins share these characteristics even though when you are looking at a glowlight tetra and a piranha they couldn’t appear more different.