Skinny body and red-tinted fins is a good clue BUT I have been fooled by fish that lacked these characteristics. Even the bottom of the tail being ragged is not reliable, though another potential indicator.

Usually the fish will exhibit one or more of these signs but I have caught spawners that appeared perfect in every detail-even a firm belly only to have them "de-flate" inthe fish box an hour later.

The best sign I have found when I suspect a bright fish has spawned is I look at the bunghole. If it is "pooched" out or protruding, that usually means the fish has spawned or has loose eggs and would be poor quality anyway.

Sometimes, it really is hard to tell-even with a trained eye!