Not a big fish ID expert, but these look like some species of Redbelly Dace (Genus Chrosomus), although I cannot tell exactly which species they are. The genus appears to not occur in Connecticut, although some are found further north in New England. Not sure how much that matters as this place doesn't appear to be a native-focused collection to begin with).
For what it's worth, I've only seen Laurel Dace (C. saylori), Mountain Redbelly Dace (C. oreas), and Tennessee Dace (C. tennesseensis) in Southern native-focused collections. It could very well be one of those, but I don't think that's likely. Was there any range maps or text describing this fish's range by any chance?
