I have a video of 2-3 inch fatheads swimming around and these have never been reproducing for months (winter-spring, room temp). I think some are male-ish by the more blunt head and dorsal fin, and some lack these features. Reproductive tube-wise they all have a tiny bit of protrusion down there. It is possible they are suffering from agricultural pollusion which contains sex hormones.
Any suggestion would be appreciated!