I haven’t heard that but I suppose it makes sense. Probably fine to feed, most fish foods do contain some marine foods. I think you can feed that, but also feed freshwater foods like tilapia.
I’m not entirely sure but if you wanna feed fillets then I’d say tilapia or what I do in my tank is catch and fillet 5-10 crappie and freeze it that’s cheaper than buying store bought fillets plus I like it more cause this way you know where the fish came from and how healthy and fresh it was