here's a good start.

http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=209347#Post209347

if you're like me though and don't like probing fish with straws, the best thing to do is wait until the spawn i think. when you find a nest with one fish on it, that is almost always the male. if there are 2 fish, the smaller is usually the male. if both appear to be the same size, 9 times out of 10 the male will be the one that attacks your bait first. having a good pair of polarized sun glasses will really help you in finding and fishing the beds. hope that helps.