To many, it is essential when buying fish that the meat is not red and discoloured, and that its quality is consistent. This can only be achieved by skilled capture, slaughtering and processing.

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    Cod and haddock can have many serious quality flaws when they are brought ashore, usually caused by injuries inflicted by the fishing equipment used and when handling the fish on board, for example if the fish is trapped in the nets for a long period of time or through delayed bleeding or if it is not allowed to bleed out completely.

    All stresses on the fish during capture and after bringing it on board before it is bled will contribute to insufficient bleeding and red fillets.

    In commercial fisheries, some of the blood in fillets is caused by stress and suffocation during the capture; but a lot of it can also be attributed directly to delayed and inadequate bleeding after the fish is brought on board.

    This is particularly challenging during large catches on board trawlers and with purse seines, as the crew will not have sufficient capacity to bleed out and gut the fish before it dies.

    To achieve adequate quality, the strain on the fish during the capture and when bringing it on board must be minimised as far as possible. The fish must me anesthetised and bled out as soon as possible while it is still alive. The bleeding should ideally take place in chilled circulating water.

    What we have discovered:

    • Stress and crushing during capture and handling on board will have an impact on the level of residual blood in the fillet.
    • The fish should be bled out as soon as it is taken on board, specially if it is stressed and exhausted.
    • Fish that are left to die pending bleeding will have an increased level of residual blood in the fillet which will not disappear after the fish is bled out.
    • Bleeding out fish in seawater (chilled or not) or in air is not an essential factor for how much blood you are able to bleed out. Bleeding out the fish in chilled seawater will on the other hand contribute to rapid cooling of the fish, which increases shelf life and washes away blood residue and dirt before the fish is gutted.
    • To maintain a high quality, it is a good option to keep the fish alive until controlled slaughter.

    What should one keep in mind during capture?

    • Both the type of the equipment used and how it is used will affect the quality of the fish. Minimising the time the fish spends on the fishing line and in the nets, as well as short towings and smaller nets, will have a positive impact on the fish quality. Conversely, fish that spends a long time in the fishing equipment (nets, cod-ends, purse seines) will be subjected to severe stress and even death before it is brought on board, resulting in more injuries from the fishing equipment and red fish meat.
    • Catch volume restrictions and codend releasers will ensure better space in the purse seine and reduce the risk of crushing and suffocating the fish or inflicting damage.
    • Repeated stress and crushing during capture, such as swimming to escape the fishing equipment, crowding or reduced oxygen supply leading to suffocation will cause an increase in the amount of blood in the muscle. A calm cod will have the whitest fillet.

    What should you keep in mind on board?

    • The fish should be brought on board as gently as possible, without using hooks or inflicting blows or crushing injuries.
    • Fish that are under a lot of stress during capture (for example being subjected to prolonged trawling periods, being trapped in a net for a long period of time) will be even less able to withstand rough handling on board.
    • The fish should be bled as soon as it has been hauled on board. It should not lie to “calm down” in dry receiving bins pending bleeding and slaughter.
    • The use of electrical anaesthetisation makes it possible to bleed the fish immediately after being brought on board.
    • Rapid cooling of the fish extends its shelf life.
    • In specialised fishing vessels, most of the catch can be kept alive on board pending controlled slaughter on board or live delivery.

    What affects the bleeding process and residual blood?

    • Fisken som er stresset og belastet under fangst og ombordhåndtering pumper blod ut i muskelen mens den er i live. Dette blodet
    • Fish that are stressed and crushed during capture and handling on board will pump blood into the muscle while alive. Neither this blood nor blood from injuries or burst swim bladders can be removed through bleeding.
    • Fish that die before bleeding, either in the fishing equipment or in the reception container on board, will have a discoloured fillet.
    • To avoid the increased blood flow into the muscle after bringing the fish on board, it needs to be bled immediately.
    • It does not matter if it is bled in water or in air, but bleeding the fish in cool water contributes to rapid cooling and will wash away residual blood and grime before the fish is gutted.
    • If the fish is bled out in water, the water temperature also has little bearing on the amount of residual blood in the fillet.
    • Fish that are gutted immediately will actually have more residual blood in their fillets than fish that are drained of blood before gutting.


    • Tobiassen, Torbjørn; Olsen, Stein Harris. 2018. Ved bløgging av levende fisk forsvinner store deler av blodet i løpet av de første 3 minuttene – Faktaark 2019.
    • Tobiassen, Torbjørn; Hustad, Anette; Evensen, Tor Hatten; Ageeva, Tatiana N.; Martinsen, Gustav; Joensen, Sjurdur; Olsen, Stein Harris; Heia, Karsten; Mejdell, Cecilie. 2018. Bedøvelse og bløgging av fisk om bord i fartøy – Faglig sluttrapport. Nofima rapportserie (28/2018)
    • Tobiassen, Torbjørn; Evensen, Tor Hatten; Olsen, Stein Harris; Heia, Karsten; Joensen, Sjurdur; Ingolfsson, Olafur; Humborstad, Odd Børre; Nordtvedt, Tom Ståle; Tveit, Guro Møen. 2018. Ilandføring av levendelevert hyse – Optimal behandling, slakting, kjøling og prosessering med hensyn til kvalitet. Nofima rapportserie (15/2018)
    • Tobiassen, Torbjørn; Heia, Karsten. 2018. Bedøvelse og bløgging av fisk om bord i fartøy – Faktaark 2018.
    • Tobiassen, Torbjørn; Heia, Karsten; Olsen, Stein Harris; Svalheim, Ragnhild Aven; Joensen, Sjurdur; Karlsen, Kine Mari; Skjelvareid, Martin Hansen; Stormo, Svein Kristian. Bløgging og holdbarhet på torsk. Nofima rapportserie (10/2016)
    • Utarbeidet av FHF. 2016. Faktaark – Stresser blodet ut i fiskekjøttet.
    • Utarbeidet av FHF. 2016. Faktaark – Lagring i blodvann eller rentsjøvann etter fangst: Temperatur på vannet er viktigst.
    • Midling, Kjell Ø.; Olsen, Stein H. (2013) Mechanical killing and bleeding. WEFTA Conference in Tromsø 9.­11. October 2013
    • Akse, Leif; Joensen, Sjurdur; Tobiassen, Torbjørn; Olsen, Stein Harris (2013) Råstoffkvalitet torsk. Gruppert i kvalitetsklasser basert på fangstskader. Nofima rapportserie (36/2013)
    The figure shows the blood loss (%) and residual blood in the muscle after bleeding the cod in seawater for 3, 6, 10, 15 and 30 minutes.

    Three minutes of bleeding may be sufficient

    How long should the fish be allowed to bleed out for? It turns out that most of the blood in the main arteries is emptied out after three minutes if the fish is left to bleed out into water.

    Almost the same amount of residual blood is found in the fish whether it is left to bleed out for 3 or 30 minutes.

    “These experiments were carried out on a small scale, but if we see the same results on a commercial scale, it may have a great impact on the bleeding process – cutting down on the processing time for each catch and reduced needs for equipment, space and water”, says Nofima scientist Torbjørn Tobiassen.

    About the underlying research

    In 2019, Nofima completed a project where the main goal was to gain knowledge about how the amount of residual blood in the muscle is affected by capture and onboard handling practices. The project was funded by the Fishery and Aquaculture Industry Research Fund (FHF).

    All the results from this project as well as results from previous trials are summarised in a brochure written and produced by Nofima, as well as in this “Worth knowing” article.

    Here, our scientists provide their advice on best practices for achieving the best possible quality of fish during capture and after bringing it on board.

    Research areas

    Capture fisheries