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Parasites in fish are harmless! –Erlingur Hauksson –Facts about the most common or conspicuous parasites found in commercially important fish and fish-products.

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Presentation on theme: "Parasites in fish are harmless! –Erlingur Hauksson –Facts about the most common or conspicuous parasites found in commercially important fish and fish-products."— Presentation transcript:

1 Parasites in fish are harmless! –Erlingur Hauksson –Facts about the most common or conspicuous parasites found in commercially important fish and fish-products

2 Parasites in fish Micro-organisms, which can cause disintegration of the fillets when the fish is cooked, such as Kudoa sp. Ectoparasitic crustaceans, such as Sphyrion lumpi on oceanic redfish Platyhelminthes, mostly in freshwater fish Nematodes, mostly in marine fish

3 Sphyrion on oceanic redfish

4 Sphyrion is common on oceanic redfish Prevalence of Sphyrion on oceanic redfish is 14-39% The “head” of this parasite cause the fish- industry trouble. Its remains has to be picked out of the fillets Female fish are more infected than males The life-cycle of Sphyrion is unknown

5 Sphyrion infections have decreased in redfish 1989 to 1993 % For 1989 no information of infestation of fish in relation to sex is available

6 Nematodes Nematodes are parasites of fish and other marine animals Parasitic nematodes reproduce in final hosts and infect other marine animals (intermediate hosts) when they are swallowed with food Life-cycles of marine parasitic nematodes, are complicated, involving many hosts

7 Life-cycle of the sealworm

8 Life-cycle of the whaleworm

9 Are nematodes harmless? Sealworms are not dangerous for humans They are as nutritious as fish. There are no cases of sealworm making people seriously ill Whaleworms seem more dangerous. They have caused people illness (anisakiasis) Persons getting ill of anisakiasis had consumed raw fish

10 Whaleworms in cod liver

11 Nematodes in a fillet of cod

12 Nematodes and fish-processing Nematodes tolerate weak saline solutions quite well. They can survive for months in 2,5% solution at 10 °C More concentrated salt solutions kill them in short time, depending on the strength Nematodes do not survive heat above 60 o C, so boiling surely kills them They can not survive freezing. After one day in 20 o C, they are all dead

13 Nematodes and the fish-market Nematodes in fish are a constant threat to marketing of fish About 5% of the total number of nematodes are still left in the fillets after inspection and cleaning on a candling table Sale of fish products decreased about 30% after a TV-program on nematodes in fish was shown, in W-Germany 1987

14 Solution to the problem Technical solutions of the nematode- problem, are still on the drawing table One (biological) solution, would be to reduce the population of the grey seal. Total number of nematodes in cod has decreased following a reduction in the grey seal population in Iceland

15 Nematodes in cod 1973-1996

16 Concluding remarks Parasites in Icelandic fish are not dangerous to people The whaleworm is the only exception Raw, lightly smoked, and marinated fish- dishes, which could be infected with whaleworm, have to be prepared and consumed with carefulness Parasites do not make fish a dangerous food. Fish is a very healthy food


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