Hey BK,
Mussuranas are pretty difficult to sex because they're just so strong. Here's what David Fabius told me a while ago:
"probing in mus is sometimes iffy, as some females probe at 8 scales deep.
Real males should be 12 and up, however there is always the middle where you dont know."
My vet and I have a pretty good record together with sexing them, but recently had one that was sexed female probe later as a male. Visually, adult males have a bulge in the vent that's pretty easy to see.
Doug T
