In biology, any group of fish that stay together for social reasons are said to be shoaling, and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling
Fish derive many benefits from shoaling behavior including defence against predators (through better predator detection and by diluting the chance of individual capture), enhanced foraging success, and higher success in finding a mate. It is also likely that fish benefit from shoal membership through increased hydrodynamic efficiency.
Fish use many traits to choose shoalmates. Generally they prefer larger shoals, shoalmates of their own species, shoalmates similar in size and appearance to themselves, healthy fish, and kin (when recognized).
The "oddity effect" posits that any shoal member that stands out in appearance will be preferentially targeted by predators. This may explain why fish prefer to shoal with individuals that resemble themselves. The oddity effect would thus tend to homogenize shoals.
So now we know why all the fish play on Party Poker! ♠_cool:
