Don't quote me on this but I believe you have to physically inspect them (if you get my meaning) unless I imagined that. Found this snippet so I was right:
Sexing: When trying to sex your synodontis, first you'll need to catch it.... Good Luck...
Next, in great care of its sharp dorsal and side fins, place the catfish's dorsal in between your index finger and your middle finger, to hold the fish on its back. (Make sure the head is towards your palm and the tail is in the direction of your fingers, that way if the catfish wriggles, your less likely to get some damage done... To you that is)Next pull the tail down gently, doing this should straighten the pelvic fins to reveal a furrow tissue underneath. The furrow will open to display the anus of the fish and the genital pore.The female will show an extended papillea but the oviduct is on the ventral side of ths papillea; if the female is mature a slight redness might be apparant. A small or thin female may have 2 pink pores, oviduct and anus. Males on the other hand have quite a ridged genital papillae on which the spermatoduct is on the back end facing towards the tail fin.
Females may apear more 'plump' also.
they are just the cutest little things, so interesting to watch. Thanks for all your kind comments.
