Milt isn't testicle. Fish keep their reproductive cells in sacks. The females have egg sacks, the males have sperm sacks. That's milt. It's pure semen and sperm, not an actual organ. The testicle in mammals is a combination of factory and storage facility, an actual organ.
I really ship Laius and Marcille now. We know it's mutual, but it's kinda sad to see that even in the ideal kingdom they're still work partners, not a couple.