Chilling of pelagic fish onboard Norwegian fishing vessels.

Wild caught fish is divided into pelagic (Herring, Mackerel) and demersal fish (Cod, Saithe and Haddock). Pelagic fish is caught in large quantities and transported fresh to processing on land. Ice was earlier used for chilling of fish, but because of large amounts of fish onboard, tanks with refrigerated sea water (RSW) has been used since the 1960s for chilling of pelagic fish. The water is chilled in a refrigeration system and circulated through the fish tanks. The efficiency of the chilling is dependent of the ratio of water and fish, species and water flow. The most common pelagic species caught are mackerel, herring and blue whiting. Each of them has different floating pattern in the tanks and the ratio of fish and water is also different depending on species. To investigate the efficiency of chilling, a fishing vessel has been equipped with temperature sensors in two identical tanks, where one of them has possibility to change the flow pattern. Temperature profiles and flow pattern from research cruises where blue whiting was caught show that small changes in flow pattern has a large impact on average fish temperature. It has given input to improved management of the RSW system.