To fillet a tuna into loins it is best to partially thaw the fish. Ice crystals remaining in the cells keep the fish from becoming mushy. <br />How to filet a tuna <br />Cut straight down to the horizontal bones, following cut lines in illustration #1. <br />Pry the loin away from the bones carefully and trim off the loin along the dorsal fin edge. <br />Then cut the bottom or ventral loin. <br />Turn the fish over and repeat.
