I had nine in my pond at one time.

Yes, they are a schooling fish so need to
have a 'bunch' of them. They get fairly large,
mine got to be almost 10 inches long. They
hang out on the surface and strike at bugs
and such. They will scare the koi into doing
the same thing at times.

Some states have banned them. My state,
Washington, has listed them as
deleterious and exotic.

kathy :-)