Livebearer sex ratios for breeding


MFK Member
Dec 4, 2017
Just putting stuff out for people who need the information:
Swordtails and platies, primarily tank bred ones, try to get as many as you can, and have a 50/50 ratio for males and females, because in my experience with every group of domestic swords/platies I've had, having 1:2 m:f trios or even two pairs, causes some of the females to change sex. And I don't mean that as in the number causes it, most xiphophorus species do it as an adaptation to replenish the number of males in a population when necessary. However in tanks this backfired, as my group of 4 swords (2 pairs) became a group of 4 males within a few weeks. I have a group of those brick red swordtails right now, it's 2 males and 4 females, but I am very weary of the group because all the females look like they're growing swords. However I think this is more result of line breeding, they've been like that since I got them, and as stated before are still dropping decent numbers of fry.
As for guppies/endlers/mollies, and limia as well, pairs work when you have a good amount of space, reverse trios you can pull off but you need to be watchful of, and of course a minimum of two females to each male is optimal.
Gambusia or girardinus I recommend 1 male per 4-5 females. The wording on that was intentional, because when you have multiple males to various females they start to form harems. Dominant males divide themselves out with groups of 4-5 females, and whatever other males are left just grow big and get dull and don't really do much.
As for the number itself you can get away with trios or 1:3 ratios, but they will be very skittish and there will be a decent amount of fighting.
I should also note that wild strains of livebearers have less problems with sex changing, eating fry, or other problems that seem to come with inbreeding.
Just my experience, feel free to add your inputs on things.