Bluefin tuna can be worth a lot of money, but only when handled properly to maintain quality and appearance. How you handle your fish will influence how much its worth and how willing fish dealers are to buy your catch; and they can easily recognize when fish have been improperly handled. Boat size, sea conditions or crew capabilities may limit what you can do but you should try to follow the steps below to the maximum extent possible. The most important things are to minimize physical damage, bleed the fish and keep it cool and moist.
Cooling a fish quickly is paramount to ensuring quality. Bluefin tuna are heterothermic or “warmblooded” meaning they can regulate body temperature to keep it higher than surrounding water temperature. They also heat up during the struggle when hooked, and it can take a long time to lower their internal temperature. During battle a fish can become so hot from exertion that it nearly
cooks itself from the inside out, resulting in a condition called Yaki or "burnt tuna syndrome." This, in turn, leads to poor quality meat. Prompt removal of blood and internal organs also accelerates cooling and reduces potential sources of chemical and microbial contamination.
On the Line - Don’t rush it. While your goal is to land the fish as quickly as possible, the longer it stays on the line, the better it is for the fish. Longer battles - an hour or more - actually give the fish time to recover by cooling down and flushing lactic acid, which was pumped into their muscles early in the battle.
Take the Shot - When harpooning a fish, take the best shot you have when you get it, but head and tail shots are preferable as they do not damage valuable flesh and scar the marketable portion of the fish.
Gaffing - Much the same applies here. When gaffing a tuna, aim for the head and/or tail. Try to gaff as far back on the tail as possible as part of this will be discarded anyway.
Swimming - This is one of the most important, and all too often overlooked steps. Once the fish is secured, attach a swim hook and swim the fish for at least 45 minutes to an hour. This gives the fish a chance to cool down and recover.
Bleeding - Once the fish recovers and before you land it you will need to bleed it. This ensures a much higher quality product. There are several ways to do this. One is to cut or rake the gills. Another is to lift the pectoral fin and make a vertical stab cut about one hand width behind its base, 1 to 2 inches long and 1 to 2 inches deep to cut the large artery in the mid-line of the fish (Fig. 1 ). The third is a tail cut, which you should only do if you are bleeding the fish on deck. Make a shallow cut across each side of the fish in the tail region between the 3rd and 4th dorsal finlets (Fig. 2 ). Again, cuts should only be deep enough to sever the main artery located just under the skin in the mid-line.
Landing - The most important point here is to minimize contact. Whether hoisting and laying on the deck, pulling through a transom door or hauling over the rail, make sure only one side of the fish ever makes contact with the boat. If you harpooned the fish in the body rather than the head or tail, the dart side will be the “bad” side and the unblemished side, the “good” side.
Dressing - Once the fish has expired and been bleed, you need to remove gills and entrails as soon as possible to reduce internal body temperature. Lay the fish on its bad side, preferably on a tuna bag or padded surface and always away from any excess heat or sharp objects. Begin by making an incision starting at the anal fin and cutting not more than 4 inches forward and around the anus. The cut should be just deep enough to open the belly cavity. Reach into belly cavity and pull out the 3 "chords" (intestine plus 2 gonads) and cut them off near the anus, so contents do not spill in gut cavity (Fig. 3). If you have a highpressure deck hose you may be able to place the hose in the belly slit and force the guts out the fish's mouth. Otherwise, remove the guts through the gill opening after removing the gills. If possible, continue to irrigate the fish with saltwater throughout this process as it will help to cool the fish and remove blood, slime and digestive juices.
Lift the gill plate and make a cut from the top of top of the plate toward the eye (Fig. 4). Pull the cover back and cut the muscle attaching the gill cover to the head.
Next, cut the lower end of the gill arch connections, being careful not to cut through the throat area as this will lead to distortion of the head area when rigor mortis sets in. Cut around the gill membranes, behind the gills up and down the length of the gill opening. Be sure to leave the crescent-shaped bone behind the gill area intact. Insert your knife under gills, close to spine and cut the upper end of the attachment point. Repeat for the other side. Grab gills and remove them and the guts with a firm pull. Remove remaining guts, stripping membranes which attach gonads to body wall. Remove as much of the dark kidney along the backbone as possible by scrubbing the backbone with a stiff brush until it is white. Then flush with plenty of water to remove coagulated blood and slime. Remove the membrane surrounding the gill collar and remove all loose skin from gill exit. Gently clean slime from outside of fish.
Chilling - If your vessel boat is equipped with a chill tank, submerge the fish for at least 1 hour in an ice-seawater slurry made with 2 parts ice to 1 part seawater. Then remove fish and pack it with ice. If you do not have a chill tank, pack body cavity with bags of ice immediately after cleaning. Cover the “good” side with rice paper to preserve its appearance, then secure the fish in an insulated “fish” bag. Make sure that any melted water can drain from the bag.
You should always consult with your tuna buyer beforehand as their preferred handling techniques may vary somewhat.
The Bluefin Initiative is a collaborative effort between fishermen, dealers, government agencies and non-profit groups aimed at promoting and supporting Maine’s commercial bluefin tuna fishery. FMI please visit us at www.bluefinbonanza.org
*Some of the material in this brochure was provided courtesy of the Woods Hole Oceanographic Institution Sea Grant Program.