RESEARCH carried out by Norwegian research organisation, Nofima, suggests that fish which is bled, cooled and stored correctly can keep for at least 24 hours before being gutted and still maintain good quality.
How the fish is handled during and immediately after catching plays a decisive role in the quality of the product. Fish is often gutted on board the fishing vessels in order to maintain a high quality. If the fish is left too long before it is gutted, it can lead to quality defects such as belly bursting, discolouration and bad smell.
However, in order to utilise more of the by-products it is advantageous if the fish is gutted on land. But on occasions the vessels receive more fish than they can deal with if the fish needs to be gutted on land. So, it would be very useful for them if the fish which is caught in the afternoon can be stored ungutted until the following day.
Nofima has, on commission from RUBIN, studied the significance for quality of the time between catch and gutting, and the optimal storage method for ungutted fish.
The scientists tested various methods used to handle cod, haddock and saithe after the fish are taken on board the boat and before they are delivered to the fish processing industry.
“In order to be best suited for being stored ungutted, the fish must be bled in water as soon as it comes on board the boat and before it is transferred to cooling in storage tubs,” says Senior Scientist Leif Akse at Nofima.
The meat of fish that is left to bleed in cooling containers with ice slurry (finely crushed ice in sea water) or chilled sea water (CSW) can become discoloured. The recommendation from the scientists is that cooling must begin as soon as the fish is properly bled.
Having good cooling on board and on land is decisive for how long the fish can be stored ungutted. The fish is normally stored in ice slurry, CSW or refrigerated sea water (RSW). The research results point to the fact that all these cooling methods may be used to store ungutted fish, but it varies how long the fish can be stored before the quality is reduced.
“Cod which is cooled in ice slurry at a temperature of -1.25 °C can be stored ungutted for up to 24 hours without reducing the quality of the fish or by-products. At higher temperatures (0 °C), the fish can be stored for around 20 hours,” says Akse.
Haddock proved to be less suited to storage ungutted than cod, and showed more signs of discolouration and smell. However, with good cooling in ice slurry on board and on land, haddock can nonetheless be stored for 24 hours without any unacceptable reduction of quality.
The scientists are of the opinion that bled and well cooled saithe caught with gear that causes a low degree of catch damage, such as long line or seine, can probably be stored equally as long ungutted in the same way as haddock or cod without an unacceptable reduction of quality.However, fish to be stored ungutted should not have any stomach contents. Net-caught saithe with high levels of stomach contents was damaged by belly bursting 24 hours after being caught.