Converting freshwater fish to saltwater

[Cliffizme2]

At a pet store I saw an orange swordtail (freshwater) be converted to saltwater and put into a saltwater tank in a matter of 5 minutes or less by slowly mixing saltwater into a bowl with the fish. The swordtail has been living in the saltwater aquarium for a couple of days now with other saltwater fish and seems to be doing pretty well. What are the effects on the fish when this happens? How can this fish do it but not any others? I think I've seen "Figure 8 Puffers" in freshwater and saltwater tanks there too.

[leveldrummer]

im not sure about the sword tail, but there are lots of fish like puffers that are brackish water fish, which means they usually live in water that is between salt and fresh, usually around coastal areas where the two mix.

[emc7]

I've heard of guppies acclimated to salt water that live happily and breed. The aquariums feed saltwater guppy fry to saltwater piscavores, and freshwater guppies to saltwater fish eaters. Cichlids are supposedly "secondary" freshwater fish, which means that at some point in their evolution, they were salt water fish. Certainly, they moved from river to river along the coast. Freshwater fish are amazingly adaptable, but saltwater fish are in trouble if the salinity drops.

[Georgia Peach]

interesting

[Fishfirst]

Swordtails should not be in saltwater, although they probably could tolerate it for some time, eventually their kidneys are gonna fail. Molly's on the other hand adapt quite well to saltwater/brackish conditions because they are often found in these conditions in the wild. I don't believe this is true for the swordtails, but someone correct me if I'm wrong.