Haha, a little while ago I got 4 black neon tetras to hang out with my 10 normal ones, as well as a siamese algea eater. One of the black neons was much much larger than the others, so he and the sae
decided to school with my penguin tetras, because they all had one large black line. Similar story when I was cleaning my tank one time, my oto cat tried to school mid-tank with the penguins. He tried for about 3 minutes until he tired out and stopped. Also, one morning I woke up to my new female betta in my breeder net hanging out with the fry, rather than eating them!