Fishermen's News - The Advocate for the Commercial Fisherman

Shelf Life: Get the Blood Out


December 1, 2019

Keep it cold and get the blood out. These are the two phrases that are repeated in conversations regarding fish quality. Keeping it cold is straightforward. Getting the blood out is not.

Blood in fish causes bruising. Often this bruising is not apparent until the fish is filleted. Bruising occurs when blood vessels rupture and blood can leach out into the surrounding tissue. After a fish dies, the blood begins to settle and coagulate into the vessels. Even coagulated blood will cause bruising if a fish is mishandled during harvesting and processing. The only way to avoid this internal bruising is to remove as much blood as quickly and efficiently as possible. The methods for bleeding fish are as varied as the fishermen who employ them, usually dependent on simplicity and cost rather than effectiveness.

The first thing to consider when deciding to bleed fish is whether the fish is alive or dead. A vigorously alive fish will bleed better than one that is closer to death or already dead. It can be hard to discern how alive a fish is with certain species. By bleeding the fish, in any condition, some blood is removed from the body and will result in a better product. It is best to bleed as many fish as come aboard.

If possible, it is best to stun a live fish as it comes aboard. While this is a common practice among large catcher processors, it is just making its way into mainstream commercial vessel harvesting. Stunning allows a fish to stay alive but keep the fish from struggling. Struggling increases lactic acid in the muscle tissue and can result in bruises as the fish thrashes against the deck, hold and other fish. Stunning can be done by percussion, electricity or CO2. Percussion stunning is labor intensive and can result in unintended bruising along the fish. Electric stunning can be done in or out of the water and is currently being tested for use in Norwegian trawl fisheries. CO2 stunning is done by immersing the fish in carbon dioxide-rich water, effectively suffocating the fish in water. This method is both impractical in vessels and shows little difference in quality from air suffocation as the fish continues to thrash until it is unconscious.

Bleeding can be achieved through cutting gills, cutting gullets or pressure bleeding. Pressure bleeding is the most effective and labor-intensive method. Because it involves special equipment, it is not practical for larger volume fisheries. The second best option is to “pop” or slice the gills. To sever the gills, fingers, knife or scissors are inserted into the gills and either pulled out or cut on one side. The fastest method is to slice the gullet directly behind the gill plates where they connect to the body. While fast, this method also opens the belly cavity to the environment and can result in a higher bacteria count. Additionally, the heart itself can be nicked in the process, speeding up death and resulting in less blood lost.

Once the fish has been cut, it may be dry bled or wet bled. Dry bleeding occurs when the fish is left on the deck to bleed. This creates a lot of blood on deck and leads to the fish thrashing against the deck and other fish. It frequently leads to more bruising. Dry bleeding is less effective because the blood coagulates as it contacts oxygen, immediately beginning to clot and stop the blood flow. This will decrease the amount of blood removed from the fish. Wet bleeding is when the fish has been submersed in either water or slush ice to bleed. By bleeding into water or slush, the blood is washed away and as it clots and more blood is removed from the fish. Water washes blood residue from the body and gills of the fish. If the water is chilled it has the added benefit of cooling the fish off faster and slowing down the growth rate of harmful bacteria.

The next decision is the amount of time to allow the fish to bleed. A recent study using wild cod in Norway has shown that most of the blood is drained from a fish within 3 minutes of being placed in chilled seawater. It does not harm the fish to remain in the chilled seawater longer, and time is usually dependent on process flow of harvest individual to each vessel.

The highest quality is achieved when fish are live bled by slicing the gills and placing them in chilled seawater. However, implementing any steps toward bleeding fish will ultimately result in higher quality of the overall catch.

Brandii (O’Reagan) Holmdahl is the Director of Quality and Regulatory Compliance with Bornstein Seafoods. Over the last 28 years she has worked in seafood production in every major region and handling most species of seafood harvested in Alaska. She has also fished on long liners, gill netters and worked on tenders. She recently spent 2 years in global seafood exports and imports on the East Coast and has returned to the Pacific Northwest to follow her passion for helping fishermen deliver the highest quality seafood available.


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