Livebearers comprise at least half of the “bread and butter” fish every local fish store has in its sales tanks. And justifiably so, as livebearers are hardy, inexpensive, colorful and interesting in their form and behavior. Many a young enthusiast (including me many years ago with my first tank) gets hooked on the hobby when a female guppy, swordtail, platy or molly (with me it was a black molly) gives birth to tiny replicas of herself.
Some store owners and fish-room managers often say they have problems keeping livebearers; the biggest problems being the fish get clamped fins and the “shimmy.” This is a relatively easy malady to avoid, but a difficult one to cure. Shimmy comes primarily from a livebearer being in too cold water for too — usually on the trip from the distributor to the store. Mollies and swordtails are the most susceptible to shimmy. Keep them in your warmer/higher tanks, and if a fish distributor shows up with livebearers that have even a hint of a shimmy, send them back, as you will not be able to sell the fish.
Salt is another topic of concern for livebearers. The vast majority of livebearers are raised in the Far East. I have found the best to come from Singapore and China. Florida fish farms also produce livebearers for the trade. In either case, the fish have been raised in water that has a fair amount of salt in it, and if they come from Singapore they have been shipped in water with even more salt added. In my wholesale fish business, the way I handled this is when I first tank the fish I add salt to their water. I use “System Saver II,” which is a water-softening salt made by Morton’s. It is cheap, and you can get it at Home Depot. Since I have been using this stuff I have pretty much eliminated any losses of livebearers. I start with two pellets (about a teaspoon) for five gallons, and after the fish have been tanked for a day or two, I do a 25 percent water change and do not add any more salt.
There are many beautiful livebearers available, and they sell well at a good profit margin. However, many stores have trouble keeping them. My experience is that you have to keep them warm, make sure your distributor keeps them warm on their way to you, and you should try using Morton’s System Saver II water softening salt.