Here is a link to a previous PBoss Forum discussion about sexing yellow perch. TJ reports he reliably determines YP sex at all times of the year.
In my experience the best accuracy of determining sex is in spring when females have swollen bellies containing eggs (prespawn) and presence of milt from males. Also a for a couple weeks post spawn the females are easily recognizable by having noticeably enlarged genial orifices. IMO at other times if you are careful and diligent sexing YP using genital orifice shape it results in 90%-95% accuracy. In my experience this technique works best on mature fish that have spawned at least once.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Main=28819&Number=369678#Post369678Cecil Did you ever ask Rob Rode why YP need a cold period for egg development if YP usually start egg development in August-September?
