All three responses are correct, especially Wakina's statement about any table fare, venison, rabbits, you gut them right away, skin them as soon as possible. Spoiled blood is natsy. (The reason for bleeding) Also the lateral line holds contaminants, especially older ones that have had more time to collect them. Three reason to zip as I see it.... cleaner fillets, no bones, less chance of PCB's or what ever crap collects there. Just my thinking, Also I think it tastes better.