Risking to be hit in the head with a hammer by graphicdesign_r :duh: , I remember that when I was a little boy, I used to go fishing with my dad and brother at the river shore, at no more than 200 ft. from the sea.
Just below a bridge, there were some brown fish that were always stuck to the stones, and I managed to catch them with really small hooks and then sat them free. As it jumped into my mind, I think they looked like plecos, and if I'm not wrong, at that distance from the sea, water would be at brackish level. I assume that, because water level raised during high tide and lowered when tide was low.