I have fish in my freezer that has a bit of freezer burn can I feed this to my Khaki Campbells, they are about 5 weeks old..........Phew they eating us out of house and home

They are on grower pellets and I'm giving the cabbage, sweetcorn, peas and all that other good stuff you guys talk about. I was thinking for the odd treat? my concern is that they are not getting enough protein or calcium. Don't want to do anything wrong![]()