That sounds a bit like a fish I had back in the day, bought it as a "silver shark" (I love made-up retail names hehe). Mine was big though, 8"-10" or so. Sounded like what you've got except without the stripe, but maybe they lose it with age? But maybe not...what I had had barbels somewhat like a koi. It had pretty large scales too along the sides, so it wasn't plain, had almost a black netlike look to it because of the scales. It was in between silver & gold, kind of like the silver feeder comets you see except lighter.
Anyway if they're the same get ready for some growth anyway. Mystery fish are the best
