You can render just about any animal out there into an edible powder. IIRC, all animal toxins are neutralized by thermo-degradation (cooking to well done)except maybe certain bacterium, which must reach a temp greater than 240 degrees. In any case, cooking all animal products to such a temperture and dehydrating them should pretty much sterilize them suitably for digeestion. You may need to trim away excess fatty deposits first, but once they've been cooked and dehydrated to a brittle stage, they should be easily ground up and usable as a foodsource, especially fish, which I believe even the bones can be thus processed and consumed by humans.

Having worked in a meat processing facility where none of the animal is wasted, the only thing that keeps us from eating all of the animal is social acceptance and the fact that there's a demand for pet food and leather upholstery. People who eat dog food are eating all the parts of the cow we would otherwise refuse, except for the hide. If it was dog chow or starvation, I think many of us would take the kibble.