To create a true anadromous fish would be almost impossible for a hobbyist the osmoregulatory systems are totally different. Some fish are of course capable of doing it, Striped Bass, Bull Sharks, Sturgeons, several slamonoid sp. et al. To cross a true freshwater species with a true saltwater species would take some very specialized science. The best chance in my opinion and this is a reach would be some type of wrasse and an some type of Mbuna or use one of the Danakilia sp. from the salt lakes of northeaster Africa in the Danakil Depression. The main issue to me is the ability of this theoretical hybrid to effectively osmoregulate in both environments, the creation of a true frankinfish. Interesting to speculate, it's highly unlikely at best.
We digress.