I got my fins wet on fresh water. I think my all time favorite tank next to my Miniature Menagerie is the pond tank I had growing up. Parents got me an acrylic tank, around 15 gallons or so. Air powered under gravel filter... the original mollies eventually died, and my parents wouldn't immediately take me to Walmart(back when Walmart sold fish) to get more... so I stocked it with fish from a pond thru the woods from their neighborhood. All kinds of stuff from warmouth to mosquito fish to a crawfish. Even had a amphibian called a siren at one point. Think axolotl, but more eel like and only front legs. I'd keep them for a little while, then take them back and catch new stuff.