You know those little plastic fruit baskets? You can place some with some cut-to size pool noodles fit to the rim, small though, so that it floats, place some floating plants inside it. Or clamp it to the surface at the side, etc. It'll be too small for most adult fish to get through it but offer a safe refuge for fry to hang out. By the time the fry can't fit through the holes, they'd be too big for the adults to eat.
Like these or similar.
Like these or similar.