Wild cod stored in a so-called “Cod Hotel”, or cod holding facility, is a top-quality product when it is handled properly and is preferably not stored for a long period without food.
This has been established by Research Scientist Tatiana N. Ageeva following three years of work on the Catch research project.
“Live storage allows us to secure and also improve on the quality of the fish at the time of capture,” says the Nofima research scientist.
Four weeks without food
Catch is a visionary project of which the objective is for live storage to provide the maximum sustainable value of wild Atlantic cod.
“By keeping the fish alive after capture, we can deal with the significant challenges associated with substantial fluctuations in quality and captured volume. This means we can achieve an extremely high and stable quality for the export markets”.
During three years as PhD Candidate in the project, Tatiana N. Ageeva has studied how the quality of wild spawning cod develops from the time of transfer to sea cages until it is distributed to the marketplace from the cod holding facility.
“According to Norwegian regulations, wild cod can be stored alive for up to 12 weeks. For the first four weeks, the fish can be left without feed. In the Catch project we have studied how staying in the cod holding facility affects the quality of the spawning cod”, explains Tatiana N. Ageeva.
She has written her doctoral thesis on live-captured spawning cod. The work lies at the intersection between physiology and product quality, and is about obtaining a better understanding of how the spawning cod responds to live storage, and thus how it affects the quality of the raw material and end products. Changes in the weight, fillet ratio and muscle quality of the fish were studied while they were stored in the holding facility. In addition, the development of rigor mortis and its consequence for product quality, were studied. Muscle quality, i.e. consistency, colour, nutritional content and capacity to retain fluid depending on season and handling, also forms part of the study.
Cod spawns in the holding facility
According to Norwegian regulations, cod that is stored alive in a holding facility should be offered food after four weeks. It is difficult to get wild cod to eat artificial feed. There is no problem if it does not have a particularly good appetite for the following few weeks, but if the fish still does not feed after eight weeks, the quality will be at risk.
“After eight weeks without feeding, the cod will have a lower protein content and a higher water content. Fillets can get an atypical white colour and gelatinous consistency”, explains Tatiana Ageeva.
The results of the study that forms part of Tatiana N. Ageeva’s doctoral work, substantiated the need for cod that is stored alive in the “hotel”, to be able to feed. This is important both with regard to quality and the welfare of the fish that is stored alive.
However, it is not necessarily the case that the captured fish feeds on what it is served. ToBø-fisk AS in Havøysund, Sjøfisk AS at Bjarkøy, Biomar AS at Myre and Fiskeriparken Egga Utvikling have therefore collaborated in finding a suitable dry feed for live-stored cod. Nofima’s researchers in the Catch project have contributed by evaluating the quality and conservability of the fish in terms of the type of feed – pellets or herring – they were given during the trials. The results for the newly developed feed seem promising.
The study also shows that the cod actually spawns while it is in the holding facility – despite being in captivity and not being fed.
“This leads to a considerable reduction in the weight of the fish even before it is used in production. The study also shows that female cod is affected more seriously by lack of feed than male cod. This was reflected in the greater loss in total weight, gutted weight, weight of liver and substantial reduction of protein content in the muscle”, explains the research scientist.
Pre Rigor Mortis
An extremely relevant question relating to preserving the quality of live-stored cod, is the time that filleting takes place after slaughter.
Just as with everything else that dies, fish also undergo a period of death stiffness i.e. rigor mortis after slaughter. Once rigor sets in, the muscle contracts, the fish becomes stiff, inflexible and its texture hardens. A fish in this condition is difficult to process without it resulting in a product of lower quality. Rigor stops eventually, but it takes time. A cod may remain stiff for up to two or three days.
The period before the fish becomes stiff – the pre-rigor period – can vary from less than two hours to more than a day after slaughter. This is very significant for the fishing industry, which prefers the pre-rigor period to be as long as possible, giving greater production flexibility.
Tatiana N. Ageeva points out that: “Fillets carved pre rigor are products of the best quality and have a long sales period, while fillets processed post-rigor are more fragile in texture and can thus more easily split up during production and lose a lot of fluid.”
Shrinkage and loss of fluid
The study she has participated in shows that the pre-rigor period is reduced when the fish has not been fed for a long time.
“All the same, after a fasting period of 12 weeks and careful slaughter, the pre-rigor period may still be long enough (up to 15 hours) to be able to process the fish before it stiffens,” she says.
How the lack of nourishment affects shrinkage and fluid loss in different products (fillets, loin and boneless pieces), is also covered by the study.
In general, it was the case that products processed early – up to 14 hours after slaughter – shrank more than products made one or two days after slaughter. This is due to the development of rigor, and occurs regardless of how long the fish went without feed. However, in this study, product shrinkage had little effect on fluid loss.