I have attempted it with raccoons, opossums and armadillos my dogs kill. Instead of fish, chickens where the consumers. A problem was the juices dripped out of the carcass too quickly as did the maggots before mature resulting in about half of the carcasses mummifying rather than converted into edible biomass. If I were to do it again, then carcasses would be placed on a cookie sheet with a little soil added. The maggots would then stay with carcass until the final instar before moving away from carcass to pupate. Then they fall to ground to be consumed. You want to keep carrion beetles away as they eat most of the maggots. Having carcass elevated reduces odds the carrion beetles will start working carcass.

Consider doing Black Soldier Flies as they can grow on a mix that is based on plant offal.