Should be slaughtered within eight weeks
Cod kept in live storage without feeding should be slaughtered within eight weeks. This is the conclusion from preliminary results from the Nofima CATCH project.
The results were presented on Wednesday at Nofima’s R&D seminar covering live capture, live storage and the production of raw materials from live captured fish, introduced by Minister of Fisheries Elisabeth Aspaker.
CATCH is a visionary project with the purpose of capturing the maximum sustainability value of wild-caught Atlantic cod based on live storage. It is financed by the Bionær (Sustainable Innovation in Food and Bio-based Industries) programme and the Research Council of Norway.
Fat cod ready to breed were captured off Andøya in Vesterålen in March 2015. Fish were withdrawn for sampling on four main occasions during the 12 weeks of live storage: after 0, 4, 8 and 12 weeks. The results show that the quality of the fish was well maintained for eight weeks after capture.
Fish in the wild also without food
The length of the period for which fish are kept before slaughter is of crucial significance because the fish are kept alive in the cages without being fed.
“It’s important to point out that it is natural for cod to experience long periods without food, such as during the winter or when breeding. Cod that have reached sexual maturity can go without food for eight weeks. After this, it starts to consume its energy reserves in order to survive,” said Tatiana Ageeva during her presentation at the seminar.
While the quality of fish remained good for eight weeks of live storage, a significant fall in quality occurred during the four final weeks of the storage period.
“The milt and roe had been nearly exhausted by the twelfth week, the size of the liver was approximately half of normal, and the muscle mass had fallen by approximately 15%. This means that sexually mature cod had coped well without food for around two months, after which it was forced to start to use its energy reserves to survive,” said Tatiana Ageeva.
Ageeva is a Ph.D. student employed by Nofima, and the principal goal of her thesis work is to obtain greater knowledge about how the quality of raw materials from cod kept in live storage changes. The objective is to obtain a product of the best possible quality.
Pre-rigor or post-rigor?
One of the projects in CATCH involves determining how rapidly cod should be filleted after slaughter and assessing the consequence of delay. Should cod be filleted in its pre-rigor or its post-rigor state?
Pre-rigor fillets are produced from the fish before rigor mortis – the stiffening of the muscles that occurs after death – has become established. The muscle in this case is as fresh as possible: it is flexible and has a naturally firm consistency. As rigor mortis develops, the muscle contracts and becomes stiff and hard.
“The stiffness of rigor mortis can last for two days. It is extremely difficult to fillet fish in this condition without significantly impairing the quality. Faulty cutting of the fillets in the filleting machine can also arise, which leads to lower yield. Cod is normally processed in its post-rigor state, after the rigor mortis has passed,” said Tatiana Ageeva, as she described how the fillet in this case again acquires a flexible texture, but becomes more easily damaged during the process.
The experiments showed that there is a large difference in length between fillets that are taken within the first 14 hours after slaughter and fillets that are taken later – after the rigor has passed.