BoomerD said:Mollies aren't actually freshwater fish, but rather brackish water. They can be acclimated quite nicely to saltwater, but of course, since this is not their natural habitat, they don't usually live as long. Many people use the s/w acclimated ones as feeder fish. Supposedly they are more nutritious than goldfish for the salt water predators.
Guppies, will adapt to full strength seawater, but will not reproduce in it.
As far as adapting mollies(which breed in any salinity!) and flounder to saltwater, replacing freshwater with saltwater as a 50/50 mix adapts them without any ill effects in two days.
This also prevents a possible pH shock.