Couldn't say really, but the females are typically larger with a bit more color. I'm presently waiting for the two convicts I kept from our last batch to NOT spawn, hoping they are both males. Convicts seem to very prolific, so just be aware of what you may be in for. I've been through 3 batches in the past few years and want no more. I found a guy to take a bunch off my hands last year, but pet stores don't want them and I ended up euthanizing most of what we had from last spring after they got too big to keep.