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How big do Swordtails grow? Which would you recommend for a 20 gal, that or Mollies?

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JackGulley

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Hi, I'm setting up my first aquarium (20long planted freshwater); at the moment I've got cherry shrimp, zebra danios, and a couple of white cloud mountain minnows (plan to get more so they're not lonely) but I'm planning to get something a little bigger for the tank in the future. I'm drawn to swordtails and mollies, especially the orange and black ones, but I'm having trouble figuring out the size of each?
From what I understand, mollies get to be about 5.5 inches, which is a little bigger than what I would like (I'd prefer about 4 inches for the size of my tank). But when I try to research swordtails, I'm finding sources claiming anything from 3-4 inches to 6-7 inches. Is the difference based on whether or not they measure the tail? Or do they just vary that much naturally? I also heard it mentioned that many fish store swordtails are cross-bred with platies; does that have something to do with it? If there is a variant that's smaller I'd probably want that one.
 
A note; as far as I can tell my tank *could* support the larger mollies, I'd just rather have something that would have a little more room in the tank.
 
A note; as far as I can tell my tank *could* support the larger mollies, I'd just rather have something that would have a little more room in the tank.
hi! swordtails grow to like 4 inches long and mollies possibly even larger.
Platies are smaller, and they would be a perfect fit for a 20g, and look just the same as a swordtail, just shorter body.
 
I’ve had 6” female Swordtails, and males about 4.5” excluding the sword. They have the potential to get this big (depending on their genetics and care, etc), but most only get to about 4” (excluding sword).
I wouldn’t keep Swordtails or Mollies in 20g. I would keep Platies, which I think I prefer anyway.
 
I think either or becomes neither here. I love swordtails, and bred them for years. The colour form ones can get too large to swim happily in a 20, even a 20 long. The same, alas, is true for mollies.
The sketchy corners of the trade started mass producing intentionally deformed balloon mollies to sell for smaller tanks, but looking at that deformation I would expect it to cause chronic pain, and that is not right. We should not buy them.
I would look at platys, or endlers in a tank the size of yours. You can't win them all....
 
Many of the swordtails (like red ones) are really hybrid with platy and don't get as large as wild swordtails. Unfortunately with hybrids you will sometime get a throwback that get larger. I find the red ones will typically stay under 4 inches and work in a 20 long; with plenty of swimming area (i said under 4 inches but the sword tail on the male can be quite long putting them slightly over); greens have been a mixed bag for me over the years and naturally wild swords can get quite a bit larger.
 
The size of the mollies and swordtails depends firstly on the genetics. Then hierarchy, temperature, food and space. And it also depends on what kind of mollies and swordtails we're talking about.
This all makes the size differ. And the sizes you've read are all correct.

Most available ones are the breeding forms of both species. Most breeding forms of mollies won't reach the size they'll reach in free nature anymore. Descendants of the Poecilia sphenops are small to mid size. Descendants of the Poecilia velifera and the Poecilia latipinna are mid size mollies. Breeding forms of swordtails do differ in their max size.

But wild specimens of both species can be very small till very large. If we just look at small wild swordtail specimens, we'll end up with Xiphophorus pygmaeus, Xiphophorus continens, Xiphophorus nezahualcoyotl, Xiphophorus multilineatus and Xiphophorus nigrensis. The only wild Xiphophorus hellerii species where the male is considered being small is the Xiphophorus hellerii Rio Jalapa. All wild dwarf swordtail species.
Below: Xiphophorus hellerii Rio Jalapa.
1702146113689.png

If we look at just small till almost mid sized wild molly species, Poecilia chica, Poecilia Vandepolli, Poecilia caucana, Poecilia arubensis and Poecilia orri.
But at an average fish store the wild specimens are rarely offered.

We're used that platies are smaller than swordtails. But that doesn't have to. But even platies ( and I'm just referring to the maculatus and variatus platies for those are most available through retail) can grow up large if the circumstances are right.
1702145511364.png

1702145546354.png

Not just a wild swordtail species as the Xiphophorus montezumae can reach up a very large size but also breeding forms can like this beautiful red male (and he isn't even the biggest one I've seen).
1702145694164.png

And here's a picture of the Xiphophorus pygmaeus.
1702145817906.png
 
Many of the swordtails (like red ones) are really hybrid with platy and don't get as large as wild swordtails
You might wanna reconsider this...
 
You might wanna reconsider this...
I can only comment on the generic red ones i had which had no species associated with them. I kept them for over 5 years (I think the male lived to be 6 or 7); first in a 40B then later in a 120 then last back in the 40B; he bred many times and i kept a few females over the years; around the time he showed extreme old age on the young female showed it true form as a male. Anyway they never got over 4 inches and had plenty of room. I do realize there are many species but finding pure species in the usa seems like a challenge; as most of the local stores have various colur morphs of some random species and even the specialties stores i use rarely have specific species of swordtails much less wild caught ones. I suspect there just isn't much of a market; i once spent two years looking for wc of a specific green species only to give up and move on as forever not available.
 
I can only comment on the generic red ones i had which had no species associated with them. I kept them for over 5 years (I think the male lived to be 6 or 7); first in a 40B then later in a 120 then last back in the 40B; he bred many times and i kept a few females over the years; around the time he showed extreme old age on the young female showed it true form as a male. Anyway they never got over 4 inches and had plenty of room. I do realize there are many species but finding pure species in the usa seems like a challenge; as most of the local stores have various colur morphs of some random species and even the specialties stores i use rarely have specific species of swordtails much less wild caught ones. I suspect there just isn't much of a market; i once spent two years looking for wc of a specific green species only to give up and move on as forever not available.
I've posted some pics earlier within this thread. Also a red male which had a nice size.
 
I've posted some pics earlier within this thread. Also a red male which had a nice size.
yea i saw the pictures and the post; was just repeating my experience. I think things might be different in europe as you can obtain specific species which is a bit harder here esp at chain stores. They used to be really popular oh well. I'll check with an importer and see what he has to say i suspect he'll say something like well your the only one who wants them i can import 100 if you buy them all.
 
Many of the swordtails (like red ones) are really hybrid with platy and don't get as large as wild swordtails.

All the old domestic Swordtail strains are hybrids. I had a Red, a Green, a Sunset and a Red Wag, all 5.5-6”, and all hybrids. In my experience they can grow far bigger than the wild types.
 
yea i saw the pictures and the post; was just repeating my experience. I think things might be different in europe as you can obtain specific species which is a bit harder here esp at chain stores. They used to be really popular oh well. I'll check with an importer and see what he has to say i suspect he'll say something like well your the only one who wants them i can import 100 if you buy them all.
Yes, that's the trick if you want to order something that is considered being rare. It's possible to get them but take a whole lot of them or you have to pay a lot for a few specimens.
All the old domestic Swordtail strains are hybrids. I had a Red, a Green, a Sunset and a Red Wag, all 5.5-6”, and all hybrids. In my experience they can grow far bigger than the wild types.
Not all domestic swordtail strains are a result of hybridization but most are. Also wild swordtails that developed a mutation were linebred to an aquarium strain.
There are small and large domestic swordtail strains. But there are also small and large wild swordtail species. I also like to add that green domestic swordtails are not completely to be compared with their wild ancestors just by looking at their color. The green swordtails you get through the commercial trade are already an aquarium strain.
 

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