My LFS gets in wild-caught sailfin mollies and swordtails from Mexico. Would they be OK in the same tank? I'm thinking of starting up a 33-long mixed livebearer tank with a trio of each, or, two pairs of sailfins and a trio of swordtails. (The LFS only sells the mollies as pairs, so I'm not sure if I could get a trio.)

I also have four tequila goodeids I was considering adding to that tank if I do move forward.

I've read that it's difficult if nearly impossible for mollies and swordtails to hybridize, so I'm not too worried about that. (Unless you think I should be!) I'm more concerned about the males competing with each other, or, harassing the other females too much.

I do have extra tanks for raising fry, so I don't expect the display tank to be a colony situation.

Thanks!

Males of both mollies and swords can be aggressive.  But individuals vary in their behavior, and seniority in the tank is also an imporatnt factor.   Putting them in at the same time often helps, since neither has a "claim" on the territory.  You'll just have to try it and see, and be ready to separate them if fighting gets too intense.  Most shops will probably be happy to sell you extra females, since many customers just want males.  The "pairs only" rule is probably to protect them from customers buying all the males and leaving them with unwanted females.

Males of both mollies and swords can be aggressive.  But individuals vary in their behavior, and seniority in the tank is also an imporatnt factor.   Putting them in at the same time often helps, since neither has a "claim" on the territory.  You'll just have to try it and see, and be ready to separate them if fighting gets too intense.  Most shops will probably be happy to sell you extra females, since many customers just want males.  The "pairs only" rule is probably to protect them from customers buying all the males and leaving them with unwanted females.

Thank you for the great advice, Gerald. I just love the wild types of these fish.