The thing about giving fish is that Vitamin E needs to also be given.
Fish is a truly great source of some fatty acids.  The problem is that
certain marine fish and mollusks, if given in large amounts, can cause
nutritional steatis (yellow fat disease), a fatal condition if allowed
to progress which kills faster in kits than adults, but which is usually
correctible.  The treatment protocol is given in Fox's _Biology and
Diseases of the Ferret_.  This is not too common these days but was for
a while among some fitch fur farmers (people who raise ferrets as a fur
animal), and a few cases that I have discussed with Dr. Jerry Murray have
shown up in the last year in ferrets given cheap cat foods.  Getting a
balanced food is really something that involves a lot of balancing of
this and that, and in the cheap foods the makers don't necessarily
care...
[Posted in FML issue 4919]