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Better Handling Means Less Mucoso

NORWAY - The stockfish industry can save millions if fish are handled correctly, resulting in less mucoso. After three years of research, fishermen and farmers are being warned to avoid storing gutted fish in seawater.

Mucoso is a condition where the fish meat dissolves and becomes gelatinous after rehydration, resulting in a considerably lower quality and therefore lower price. The industry itself estimates that mucoso causes annual loses of around NOK 40 million.

Nofima Fiskeriforskning has just completed a research project on mucoso in stockfish, which has revealed that relatively simple methods can limit the losses.

”Avoiding seawater when gutted fish is handled on board the boat and during processing results in less mucoso,” says Scientist Ingebrigt Bjørkevoll.
"The fish should not be gutted when taken aboard," says Scientist Ingebrigt Bjørkevoll, adding: "If this is done, the fish must be stored in dry containers. Handling of the gutted cod prior to being hung out to dry must involve as little salt water as possible."

Avoiding seawater will also have other benefits than reducing the mucoso problem. Fewer fish are attacked by fly larvae, which is another major problem for the stockfish industry.

If mucoso develops, this must be removed along with the backbone after the soaking process. The fish meat often dissolves along the backbone, but can also occur in the meat close to the fish's anal orifice.

Three-year period

The research project included stockfish from Ballstad, Værøy and Røst. The trial lasted three seasons in Lofoten and involved more than 1000 fish per year.

The trials involved non-gutted cod supplied by boats which only had a short distance to travel from the fishing ground. The fish were then divided into four groups, which were stored:

  • Non-gutted in sea water
  • Gutted in sea water
  • Non-gutted in dry container
  • Gutted in dry container
Millions can be saved and earned in the stockfish industry if fish are handled correctly during the first 24 hours.
After 24 hours, the fish were hung out to dry in the normal manner. The 24-hour delay was designed to simulate a longer transportation period from the fishing ground to purchaser. The fish in the study were tagged and hung out to dry at the same place.

The study clearly showed that what the fish was exposed to during the initial 24-hour period, was reflected in the quality four months later. If there is less mucoso in the fish, both the producer and exporter gain a higher price.

"In good stockfish years, this new knowledge seems to be of less importance. But in poor years, when drying conditions are bad, it can be extremely important," says Bjørkevoll.

Further challenges

The scientists believe bacteria can be the main reason that mucoso develops in stockfish. Climate also plays a major role. Wet and mild weather during drying results in more mucoso.

"This indicates that bacteria lead to the fish meat becoming soft and dissolving," says Bjørkevoll, reiterating that this is removed before the stockfish reaches the consumer.

The project is being financed by the Norwegian Research Council and the Fishery and Aquaculture Industry Research Fund.