I just got a tank and among other things it came with two rainbow fish. I haven't yet figured out what kind of rainbow fish or, in fact, if they are even of the same type. One, however, is very sleek and brightly colored and the other is a little more subdued in colored and pretty round in the belly.
Just tonight they've started sitting still next to each other, head to head and tail to tail, and vibrating. Is this mating behavior....or just rainbow fish having fun?