I still can't get any fish eggs. I have one of every other type. I think the river is mocking me and saying, "Oh hell no, you're not gonna get any eggs from me. I'm gonna torment you by only giving you fish even though you need that river egg. Too bad, you're my ***** now. Mwahahahaha!"
I caught all of mine in the river. They're medium sized (so bigger than a crucian carp but smaller than a black bass) and they're a little bit elongated. The shadow was the same every time so they became pretty easy to spot after catching one or two. Hope that helped!