Oh! Sorry B-Gray you asked what is a rainbow runner? Well, the best way I could describe it is a tropical steelhead that has been doing the nasty with a tuna.They are species of fish that is alone in it's genus(I think)but are long,strong, and slender like a steely but with a forked tail like a tuna.Also very colorful like some kinda fish you'd see in a tropical fish tank. The local mexicans call them Salerma.Hope this answers your question as it is a hard fish to describe.