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I have NO idea, only caught them in commercial nets.

Further to my processing technique, I forgot to add you take the whole belly flap off with the head (down to their ringpiece) then scrape out the "marrow" that lies along the visible spine. Failure...

Key thing with rig is to immediately "trunk" them- whack their head, tail and fins off so they bleed out quickly. The ammonia in their blood taints the flesh otherwise. I worked on commercial boats...