prevent a fish from appearing...

[Xylem]

Hi,

I recently upgraded to GA2 and am emjoying it greatly. It's been so long since I fooled with the controls, though, that I can't remember how to do some things. (I also searched and couldn't find an answer).

Specifically, is there a way to prevent a certain fish from appearing in a given tank. For example, I think some of the darker ones don't show up well against the gravel in the Pond, but can't find a way to exclude them.

Thanks...