Circle trout are very rare... Oncorhynchus anusswimus
They are thought to be closely related to the corn-eyed brown trout, but nobody has ever been able to properly identify and document them.
This is largely due to the fact that when the circle trout is alarmed, it begins to swim in tighter and tighter circles until finally the trout swims up it's own ass and ceases to exist. A sport fishery did exist for circle trout in the early 50's, but it quicly died out as anglers sought out fish they could actually catch...

A casual invitation / threat used by an individual that is not afraid of fucking someone up.