How Do You Tell Sexes Apart In Synodontis?

[fishnovice]

My upsidedown catfish has developed a big fat round belly. How can I tell if it's a female full of eggs? Worried - Can she become eggbound?
I have 2 slimmer crossbred synos in another tank. Should I put the "fat"one in with them?

 

[fishnovice]

My upsidedown catfish has developed a big fat round belly. How can I tell if it's a female full of eggs? Worried - Can she become eggbound?
I have 2 slimmer crossbred synos in another tank. Should I put the "fat"one in with them?

Just noticed that one of my crossbred synos has lost most of his dorsal fin. All his other fins and tail are fine and he's swimming ok(upsidedown as usual)Is it finrot or has he been attacked? My convict cichlid had a nasty bite 2 weeks ago and other cichlids have died suddenly. Not sure if a hybrid Malawi or the other syno might be attacking tankmates