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I have about 12 swordtail fry and 4 guppy fry in a 10 gal tank. I was wondering how old the swordtail fry have to be to determine sex. they are about 2 weeks now and the guppys are about 1 month. The guppy fry also have not developed any color either. Am I doing something wrong or does it usually take this long?

the swordtails should be pretty easy to sex, as soon as you can clearly see the shapes of their fins. the females have a normal looking triangular anal fin, and the males have a tube shaped anal fin that lays horizontal. The males wont develop swords for a while i think, and you dont really need to rely on that to sex them anyway. I have 2 male swordtails that I selected out of a tank of mostly female fry when they were about 1/2-3/4 of an inch long, they were very easy to sex then.

I can't give you specific numbers because of the variance, but it can take a while for even the anal fin in males to change into a tubular shape.
One of the factors is the tankmates. I had four platy/ swordtail hybrids that looked female but after several months, two of them developed swords and their anals fins changed.

I had 5 baby swordtails 3 are male 2 are female. Two of the males grew their tails fairly quickly the other has grown a lot bigger than them and I though it was a female as it was growing at the same rate as the females but with in the last 2 weeks his anal fin is now tubular and his tail is beginning to point. The two female are now pregnant.

Last edited by tessa38uk at 22-Nov-2004 10:04

http://www.greenspersonalprinting.com/

It also depends on the sword, as the Monizuma, you can't sex them till there about 2-3 inches.

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There is always a bigger fish...

the average for telling the sex of guppies, is 4-5 months, it is like 3 months for swords i belive, i have 7 sword fry, i thought i had an older 1, but i think it may be a platty i think the mother may have been a hybrid, or a fancy sword, it is like an 1 inch now, and many months old, so i am thinking its a female, but before u set ur heart to a sex, it could change easly, thats what happened to 2 of my very first guppy fry, out of oo i dont remember how many, i have 3 left, a big one, a medium one and a small 1, the big and medium are male and very colorfull, the small one looks like to be a female, and not so colorfull, she may look like her mother, but their mother died soon after they were born but now i have over a hundered guppy, platty, and sword fry, its very exciting when u get new fry

Thanks for the advice I guess I will just have to wait longer to sex them. I noticed today that the mother of the swordtail fry is pregnant again!! I had already seperated her to another tank by herself because she is very aggressive, she actually bit off the sword of her male counterpart and he died soon after. I already have about 20 or so fry in my 10 gal and the tank she is in is just 5 gal and she is alone. Should I try to transfer the newest group of fry, or would that be too many. I would like to give them away when they are big enough but I am worried about overcrowding.

Oh dear that's sad about the female killing the male It was the other way around with my 2 the male killed the female in the end with his pestering He is also dead now but they left me with 5 babies 3 are male 2 are female. and as I said before the 2 females are both pregnant now.

Last edited by tessa38uk at 25-Nov-2004 01:07

http://www.greenspersonalprinting.com/

Hi Buterfli782, you have a nice breeding colony,now and they will not stop breeding, until it gets a lot cooler.Trying to sex young fry is very difficult and even if you manage to sex them and seperate them into seperate tanks, they can still change sex if need be and still breed in most situations. I am sad to say this is Swordtail keeping at its best. Good luck. Muss