Originally Posted by happyfish2131
I need help, I want to know how you can tell the difference in swordtail babies like my swordtail just had fry and I can't tell which ones a boy and which ones a girl P.S some have dark long fins at the end and others just have a little line of on there tail fin..
You'll need to be patient as you can't sex swordtail fry. When the males become sexually mature, their Anal Fin will roll up and become the Gonopodium ( male sexual organ in livebearing fish) and they will grow their sword on their tail. Until this time, the only other thing you can observe is if some of the fry start to grow larger than the others, there is a greater chance that these are females. No guarantees however.
BTW: if your next question was "when will this happen?", it can depend on how well you keep your aquarium as improper conditions and poor diet can inhibit growth and maturity. Also, in some cases, not all males in one spawn will mature at the same time.
Hope I got you covered. Just be patient and enjoy the ride.