Hi Quillshoggie
I would rely on the advice from Vale Wildlife. They have a lot of experience with hedgehogs and are generally accepted to be one of the authorities on good hog care. The RSPCA deal with all animals and do not specialise in hedgehogs in particular. Some years back there was a theory doing the rounds that hogs should not be fed fish food. Where it came from no-one seemed to know. But, it became very widespread and in some cases has persisted. Probably in reality, you wouldn’t want to feed hogs on actual fish, but fish cat/dog food probably has very little fish in it. But if you are concerned, there are other flavours of cat/dog food widely available. i.e. chicken flavour, which I tend to use, but if there was no choice I would listen to Vale Wildlife and accept that fish flavoured cat/dog food is ok.
I am assuming you are talking about wild hedgehogs here, where what we offer them is supplementary to what they find for themselves in the wild.