PHOTO BOX AIDS FISH BUYERS

Photo Box Aids Fish Buyers – Researchers at Nofima in Norway have developed a prototype of a photo box with standardized lighting which can provide fish buyers at auctions with important information.

Herring and mackerel are caught in seine nets, and the fishing boats can often land hundreds of tonnes at a time. Fish buyers bid on the catches through an online auction system, often while the vessel is still out at sea. The boat can then go directly from the fishing grounds to the reception station that won the auction.

When the buyers bid on the catch, they are informed of the amount of stomach content the mackerel has. The fishermen take random samples and indicate the stomach content amount on a scale from one to four. If the fish has a low stomach content it is suitable for food products, whereas fish with a high stomach content are often used as bait and therefore sold at a lower price. This information therefore helps buyers determine how much they are willing to bid.

It is only when the fishermen bring the catch ashore that the buyers can take a look at what they have bought. If they are unlucky, they may find that they have bought a “pig in a poke”.

“The buyers are only told how much the fish has eaten. The problem is that they are not given any information about the actual stomach contents”, says senior researcher Stein Harris Olsen.

For what the mackerel has been feeding on is quite important. Mackerel eat fry from herring, sprat, sand lance and other fish species, but also krill, zooplankton and small shelled swimming snails, also called sea butterflies. The swimming snails are beautiful to watch, and are quite tasty to the mackerel, but they contribute to a deterioration in the quality of the mackerel.

When a swimming snail enters a mackerel’s stomach, the digestive system of the mackerel is put to the test. The snail’s shell is very hard, made up of aragonite (a calcium carbonate), which forces the mackerel’s digestive enzymes are put into full gear while there is a significant increase in stomach acid in order to break down the shell.

If the fish is caught and dies before the stomach content is digested, the digestive process continues nonetheless. The enzymes keep breaking down tissue and muscle fibres, which can in turn lead to deterioration of the abdominal and intestinal walls of the fish. If stomach acid and enzymes leak into the fish’s abdominal cavity, the abdominal wall will deteriorate in a matter of hours, and the bones in the abdominal wall will fall apart. In some cases, the enzymes and stomach acid will create holes in the abdomen, and the fish meat will become soft, damaged and eventually spoilt.