Vent it. Some SB's are difficult to sex because their body shape is warped.. I can't see its dorsal fin clearly either so I can't aim for the dorsal spot.. Just catch it, flip it around and look at its sexual opening. If the opening looks like a V, its a male, if its more like a U than its female. The anus is the dot closest to the head, the vent is located under the anus, closer towards the tail. If you can't tell, take a few pictures and post em.