^^What he said. These cats can't be reliably sexed with anything other than a scope. The only method I've heard of is to have a batch of similar-age, similar-fed individuals and to pick out the plumpest (considered as female due to ovaries displacing more internal space than testes) and leanest (considered male) specimens. Several scientific studies can be cited that describe a possible sexual dimorphism in ecats by way of differences in the electrical output signal wavelengths of mature specimens during their natural breeding season. But, there are many disagreements in these papers. Plus, it wouldn't be feasable to try duplicating the lab setups on a hobbyist level.
These cats are thought to be bank mud-cave spawners by some and under-log/rock spawners by others. There's never been a successful spawning in captivity.
seems you can get an home ultrasound kit for around $4,000. Plugs right into your laptop or desktop computer. Might even be an app for iphone by now lol. So yeah, apparently this is a really good way to sex catfish and some of the hatcheries have started using them as well now that the price is dropping. Exploratory surgery use to be used as well. Catfish(most species) have very little sexual dimorphism. Very extremely hard to sex non the less. Good luck. 
