Swordtail question - The Planted Tank Forum
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post #1 of 8 (permalink) Old 09-17-2020, 05:40 AM Thread Starter
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Swordtail question

At what age should I be able to tell if a swordtail is male? I have a number of swordtail fry, some almost to sub-adult size. So far, none have grown a sword. Am I just unlucky, or does the sword not develop until they're near breeding age?

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post #2 of 8 (permalink) Old 09-17-2020, 12:54 PM
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At what age should I be able to tell if a swordtail is male? I have a number of swordtail fry, some almost to sub-adult size. So far, none have grown a sword. Am I just unlucky, or does the sword not develop until they're near breeding age?
Swordtail strains develop secondary sex characteristics at widely different rates. Some strains produce many early developing males which may sex out by 90 days of age and at a very small size. Other strains selected for late developing and large adult size males may be nearly a year old before developing their gonopodium and sword. The black swordtail with metallic blue/green scales is such a fish. Males develop very late and the males often grow quite large (unless stunted with poor care).

Swordtail hybrids with fairly recent crosses to variatus or maculatus platy strains are often the very slowest to mature and males in particular are often sterile. I made a cross in the past with variatus x swordtail which developed into a group of about 2 dozen mostly male offspring of very large size (about 2x the size of variatus). These mostly male hybrids did not begin to sex out until nearly 18 months of age. They were also sterile.
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post #3 of 8 (permalink) Old 09-17-2020, 04:41 PM Thread Starter
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Swordtail strains develop secondary sex characteristics at widely different rates. Some strains produce many early developing males which may sex out by 90 days of age and at a very small size. Other strains selected for late developing and large adult size males may be nearly a year old before developing their gonopodium and sword. The black swordtail with metallic blue/green scales is such a fish. Males develop very late and the males often grow quite large (unless stunted with poor care).

Swordtail hybrids with fairly recent crosses to variatus or maculatus platy strains are often the very slowest to mature and males in particular are often sterile. I made a cross in the past with variatus x swordtail which developed into a group of about 2 dozen mostly male offspring of very large size (about 2x the size of variatus). These mostly male hybrids did not begin to sex out until nearly 18 months of age. They were also sterile.
Thanks. I have the common orange sunset swordtails starting out with 1 male and 5 females. I recently broke down my 20L and put them and their fry in my 75g community tank. The angels did a number on the smaller fry but about 8-10 were big enough to survive. I would like more than 1 male in the tank with that many females. So I'll wait and see if any turn out to be males.

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post #4 of 8 (permalink) Old 09-17-2020, 05:31 PM
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If you want more males for their appearance, I understand but one male sword will have no problems at all keeping 5 females gravid at all times.

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post #5 of 8 (permalink) Old 09-17-2020, 08:25 PM Thread Starter
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If you want more males for their appearance, I understand but one male sword will have no problems at all keeping 5 females gravid at all times.
That is what I have now for adults. I have 8-10 juveniles. If they all turn out to be females my male is going to be exhausted (with a smile on his face ). I'm also thinking that having another male will keep the breeding going longer.

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post #6 of 8 (permalink) Old 09-18-2020, 01:33 AM
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Oohh ok, so this is something I actually know how to answer thoroughly since the lab I worked in in undergrad worked specifically with swordtails! So!

With pure bred (no hybridization) Xiphophorus variatus, malinche, birchmanni, and cortezi, the fry usually had some early developing males by three months. This was with twice daily feedings of BBS (microworms if no BBS available), and a tank temperature of 76 F.

That being said, evolution kinda decided to pull a skid turn. Swordtails (and also other poeciliids) have these things called early developing males and late developing males. Some males will develop their sex organs very, very quickly (90 days at earliest), at the cost of having stunted growth. Other males will develop their sex organs much more slowly, and therefore be much larger in size and more colorful. With female swords, we tried to separate their brothers out by three months, and did continuous tests. However, at around 3 months, it was usually pretty visible which fish were producing gonopodia, and which fish had more of a fan shaped ventral fin.

If I remember, orange sunsets are some variation of X. helleri crossed with X. variatus, and maybe some X. montezumae in there as well. Never managed to grow my fry out to adulthood, but the males in the lab I worked with, usually grew tiny stubby swords by 4 months of age. The lab fed a staple algae flake if we didn't have the time, but most days I was feeding repashy soilent green, and for the fry that had graduated from BBS, a little bit of Repashy spawn and grow.
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post #7 of 8 (permalink) Old 09-18-2020, 01:43 PM
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Oohh ok, so this is something I actually know how to answer thoroughly since the lab I worked in in undergrad worked specifically with swordtails!
If you're allowed, I'd love to see a thread about your experiments and experiences with swords in the lab!

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post #8 of 8 (permalink) Old 09-18-2020, 10:19 PM
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If you're allowed, I'd love to see a thread about your experiments and experiences with swords in the lab!
Oooh hahaha, I actually don't know if I'm allowed to talk about the experiments. Something something academics can be bloodthirsty and steal other academics' papers something something.

The swords on the other hand were interesting. Jumpy fish (so. many. fish chips.), and I think I might have forgotten what hobby swordtails looked like for a bit, if only because the wild type looks so much different than the captive varieties. Fairly easy fish to work with, but we did have to watch out for fry predation in some species.

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