Four things are key to delivering fish of the highest quality: removing the fish gently from the sea; bleeding it quickly; keeping it cold and avoiding blood from collecting around it. This will ensure that the customer gets the quality of fish they are looking to buy.
Fresh fish is an increasingly important product for Norwegian fisheries. Fishmongers and market-based consumers alike prefer fresh fish which has a shiny skin, smells fresh, has a white neck and delicate flesh. The actions of the fishermen play an important factor in the consumer’s dining experience.
Researchers at Nofima have carried out a series of research trials on the quality of fresh fish and documented the requirements for guaranteeing the highest quality fresh fish for the various markets. The work has been carried out in collaboration with the Norwegian Fishermen’s Sales Organisation and supported with funding from the Norwegian Seafood Research fund.
Make sure that the flesh is white
“White flesh is a determining factor in quality. A reddish hue to the flesh can be attributed to blood in the muscles as a result of capture equipment, onboard treatment or a stressed fish”, explains scientist Torbjørn Tobiassen.
If the fish has been subjected to physical stress such as being hit, crushed or dropped, it can bleed into the muscle and under the skin, and the flesh acquires marks similar to bruising.
A fish normally uses the dark muscle closest to the skin, but when it becomes stressed or tries to get away, it uses the white part of the muscle. The fish then pumps blood into the small blood vessels and the white flesh acquires a reddish colour.
The fish becomes more stressed and the muscle takes up more blood the longer it spends on the line or in the net, or if it is squashed in a large catch in a trawl sack. The flesh will also turn redder the longer the fish is left before being bled.
Once the blood has reached the small blood vessels, good catch management is harder to achieve. But researchers have proven that cod can empty blood from their white muscle after about six hours if they are stored alive before being killed.
“The key to ensuring white flesh lies in stopping the fish from pumping blood into the small blood vessels of the muscles. Gentle fishing and immediate stunning, killing and bleeding are the best starting points for achieving fine white fish flesh”, says Tobiassen.
Bleed the fish quickly and keep it cold
Both the bleeding conditions and the temperature of the fish are very important for ensuring a good shelf-life until it reaches the European dinner table.
A live fish onboard a boat will get stressed, and the longer it sits before being bled, the more blood will seep into the flesh. Researchers therefore recommend that a fish is bled and cooled immediately after being taken on board, or stunned until it can be bled. The fish can also be killed by a blow to the head.
The fish should be left to bleed out for at least 30 minutes before being chilled to zero degrees. It is best to lay the fish straight onto ice as soon as it has bled out.
If the fish is left in bloody water in temperatures of up to ten degrees for a long time after bleeding, it will have a detrimental affect on its smell and appearance. High temperatures will very quickly start the fish’s decomposition process.
“Freshly caught cod which is kept at a temperature of ten degrees for a day before being chilled to zero degrees will have a shelf life that is four days shorter compared to that which has been chilled immediately”, says Torbjørn Tobiassen.