With L#'s it's hard to tell until they're adults, with some species it's the dorsal and anal fins and with others it's their markings, as far as the L200's go it's their spots that makes it the easiest to sex them,but mine are still too young to tell for sure, I mostly judge by their behavior. The male will take up a cave and try to trap the female in,he'll also swish his tail while in his cave to persuade her to come have a looksy 
(that's what mine keeps doing )
(that's what mine keeps doing )
