
(See here.) Fish were mentioned by an unnamed fisherman in random coastal encounter in Fallout and by San Francisco citizens in Fallout 2 as food.
Though fish do not appear in an other Fallout game, except for the cut fish that were meant to be an consumable item in Fallout 2. Other dialogue options lead to Cass saying that she has never seen a real fish, only a plastic one on a wall in a bar (that used to sing, according to the bar owner and much to Cass' disbelief). She also describes it as a bird that stays underwater, and that some of them have legs. She replies that a fish is like a slimy lakelurk thing that doesn't have claws and doesn't attack people. When you ask Cass why she took up caravaning, she responds by saying she "took to it like a fish in water." The Courier has the option to be ignorant and say "What the hell is a fish?", or can alternatively, by passing an Intelligence check, test her knowledge on the subject. In the deeper parts of the Eastern Virgin and Virgin River. In the waters near Cottonwood Cove and Lake Mead cave.
It is unknown how the fish survived the radiation as it changed other sea creatures into lakelurks and mirelurks. There are two kinds of fish found in the game: the one in the image is a largemouth bass, unchanged by radiation another is a smallmouth bass while the other fish are found in schools and appear to be perch or minnows. They cannot be interacted with by the player and are therefore considered scenery as well as a creature, similar to the birds from Fallout 3.