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How To Care For Your Tuna

Imagine catching or spearing the fish of a lifetime only to have the meat completely ruin. This is why I feel it’s extremely important to share the process of properly caring for your fish after the hunt. To learn the process of caring for your fish, we have to look at the people that depend on the quality of the meat in order to earn a living.

Commercial fishermen know the process better than anyone. Over the years, I have spoken to fisherman and spearfishermen alike about this process. Recently, I saw an amazing post from a commercial fisherman named Dennis on a forum. He broke down how to properly care for tuna once onboard the boat, and why we do this process. Proper caring for the fish can have a huge impact on the quality of the flesh. This is why I put this information together to share with you all!

Commercial fishermen as well as any seasoned spearos understand the physiology of their targeted fish. Understanding your target fish species behavior is one part of hunting, however understanding your target species anatomy or physical makeup separates the experienced fishermen from the novice and intermediate ones.

Tuna are warm blooded fish while most other fish tend to be cold blooded. Being a warm-blooded fish, the prep and care after being caught is very different from other fish. Different tuna types are unique to each other when it comes to body temperatures. Bluefin can raise their body temperature the highest out of all the tunas, followed by Big Eye tuna, and then Yellowfin. Because of this, it is very important that the fish is properly dealt with after capture.

Braining the fish

Once the fish is either on the deck of the boat or in your control, you should stab it in the brain. This action immediately kills the fish, reduces suffering, and stops the fish from thrashing around causing damage to the flesh, and you or your spearfishing equipment. Stabbing or spiking the fish does not stop the heartbeat and other organs from functioning, but the fish is now considered “brain dead”. Remember, even though the fish has been brained and rigor mortis has started, the heat exchange process is still occurring due to the autonomic nervous system and involuntary muscles actions. The fish needs to be bled.

Bleeding the Fish

First, let’s look at why and how this warming process works. The ability to generate body heat occurs due to a heat exchange. The blood flowing from the body into the heart through the gills and back into the body accomplishes this rise in body temperature.

The key to this process is the darker colored muscle along the lateral line of the tuna. This area of muscle contains a large number of blood vessels that transfer heat to and from the heart. The lateral line area also contains nerves which control the voluntary and involuntary muscle movements. The voluntary muscle moves due to connective tissues (tendons and ligaments) that the fish consciously want to move. For example, movements like swimming and turning are voluntary muscle actions controlled by these nerves. The involuntary muscle actions are not under the control of the fish. The autonomic nervous system controls these movements such as the fish’s heartbeat, and shivering. Shivering creates body heat which warms the fish in cooler temperatures the same way that our bodies function. This shivering is possible due to the energy compounds within the muscle cells themselves which are triggered for release by the nerves connected to them. The blood then regenerates more energy compounds in order to continue to warm the body as necessary. This process creates lactic acid as a byproduct within the muscles. The blood would then take away this lactic acid to the organs where it would be disposed. This is why we bleed fish. Bleeding a fish will pump the lactic acid out of its body and stop it from creating a sour taste to the meat.

The best way to accomplish draining the fish of all its’ blood is to stab vertically along the lateral line right behind the pectoral fins on both sides. Next, cut along the lateral line at the base of the tail. This process completely drains the blood from the fishes’ muscles and organs. Cutting the gills is another way to bleed a fish, but it does get some of the blood out from the organs. However, it is still better than nothing.

Gutting the Fish

The best time to gut your tuna is after the fish is completely bled out and the fish has gone into rigor mortis. This ensures that all the lactic acid within the animal has been drained out. The heart has stopped pumping, and now is time to remove the other organs. My process for this is simple. First, I like to use a shorter knife for leverage when doing this. Make a small 2-3” cut above the anus of the fish. Then I grab the anus tube and cut it with my knife. Next, we will remove the gills. This can be done by making a few selective cuts around the gill plate. Make sure you cut both top and bottom portions of the gills. Now, grab the gills and carefully pull. This should bring the gills out with the organs. The make sure when gutting the fish, you leave the membrane that separates the gut and rest of the fish intact. This membrane protects the meat from bacteria in all fish, not just tuna. Finally, we can move on to the chilling or brining process.


Now that we have bled, and gutted our fish, it’s time to put it on ice or in the brine if you prefer. First, unless the fish has gone into rigor mortis and is no longer shivering or you have destroyed its spinal cord, it should not be placed on ice. Why? Because the tuna will continue to generate heat through shivering in order to warm itself, and ruin the flesh. This is not the case with cold-blooded fish. You can and should put cold-blooded fish immediately on ice.

The fish method of chilling the fish is common among commercial fishermen using a stainless-steel punch to destroy the spinal cord of a tuna. This process prevents the fish from being able to shiver and produce heat. The punch technique is not difficult to learn, but does require some attention to detail. In short, the punch goes in at the base of the brain and runs right on top of the spine. There are several instructional videos out there to help you learn the technique. Once the spinal cord has been destroyed, you can place the fish right on the ice or in a mixture of water and ice.

The next option if using a punch is not available is to keep the tuna in a cool place with a wet towel on it, or in a kill bag with saltwater cooling it down until rigor mortis starts to occur. When rigor mortis settles in the fish has used up all its’ energy in the muscles and heat will no longer be generated. Now it is time to place the tuna on ice or in a mixture of water and ice.

Ready for the brine.

The last method that some people prefer to chill their fish is by placing it in brine first before icing it. The brine is a mixture of pickling salt, water and ice. Personally, I do not do this step, but I know a lot of people who do. According to one albacore tuna fishermen, the fish only need to be in the brine for about an hour. After that the fish, it is ready to be iced. I have also seen fishermen brine the tuna after filleting it and right before cooking it.

Recap of Steps

1. Brain the fish

2. Bleed the fish

3. Gutting the fish

4. Chilling or cooling the fish

I hope you found this useful, and good luck on your next tuna trip!


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