Where you are, you should have at least two distinct species of Fundulus killifish (heteroclitus as well as diaphanous), with the possibility of a third if you are south enough. F. diaphanous, the banded killie is pure freshwater (the other likes some salt). I have never seen them anywhere but over sand, where they feed by picking though the substrate. They are our local version of Corydoras, as far as their niche/lifestyle goes.
It was legal for me to catch and keep then, so I brought some home and they bred in a pond. I now live 800 km east of where I kept them, and there are slightly different forms here. What were pale green fish inland are a prettier bronze fish here along the coast.
I met some University of New Brunswick scientists who were studying the brackish species, F heteroclitus, as locally they are found breeding and thriving in water nothing should live in. They have lived for generations in a stream that meanders through an oil refinery. In places along the US coast, they also live in hyper polluted water and the researchers want to know how they can adapt. So these little fish come from a good family with increasingly well known cousins (the local name along the coast for heteroclitus is mummichog).
They'd be good aquarium fish if their life cycle didn't need winter conditions.