Does anyone know how to sex young black widow tetras without comparing sizes of adults? I have 5 of these tetras, 1 female and 4 males. I want to get some more females because the boys are wearing out the one I have, but i don't know how to sex them while their small, and none of the shops near by have adults for sale. Are they like other tetras, where bellies on females tend to me more noticeable and more 3D than on males? I was looking at some in the store today, and thought I could see small differences between some of their anal fins, is this a way to tell? When I look at my female her anal fin has more of a 'lobe' shape than the males, theirs are very sharp and angular.. Am I on to something with this or do I just have a female with a deformed anal fin?