I had the same problem. brought them home..dead withing a week
I put it down to the trickle fed tanks they are kept in. It gives ultra clean water conditions, and when the fish are put into our cycled tanks their immune systems are overloaded and tend to die from anything from finrot to bacterial infections.
With no outward symptoms that sounds like a bacterial infection to me. Treatable if caught early.
I found a small pet shop that kept all their fish in cycled tanks and bought some from him, and guess what...... 5 fish , no deaths or illness
. " of the famales have already had fry
.
Trickle fed tanks are used in specialist shops to make the care of the fish easier with cleaning and topping up tanks when fish are sold. But sadly there is no way we can reproduce these condtions at home, so we end up with dead fish
Plus most live bearers these days seems to have a low immune system due to inbreeding and transportation. Its strange ..some seem to do great and have no problems..yet others will just drop down dead
Luck of the draw depending on how healthy and strong the fish is.
Try getting fro another breeder. Buy about 3 and put them in an isolation tank. Have to hand Anti white Spot/Fungus finrot/Bacterial infection medication. Beacause live bearers will most likely be affected by one or sometime all of these.
Aquarium salt is good for the water also and melafix. That way you got all bases covered and give the fish the best chance. Just watch them realy carefully for the first 5 days or so, and at the first time add the meds to the isolation tank.
Now I always have a tank set up with salt and melafix/stress coat and zyme already in for new comers. And I have not lost a fish since.
Hope you have better luck next time
