Parasites in fish are harmless!

– Erlingur Hauksson

– Facts about the most common or conspicuous parasites found in commercially

important fish and fish-products

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

Sphyrion on oceanic redfish

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

Sphyrion infections have decreased in redfish 1989 to 1993

0

5

10

15

20

25

30

Males Females Total

19891990199119921993

%

For 1989 no information of infestation of fish in relation to sex is available

For 1989 no information of infestation of fish in relation to sex is available

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

Life-cycle of the sealworm

Life-cycle of the whaleworm

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

Whaleworms in cod liver

Nematodes in a fillet of cod

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 oC, so boiling surely kills them

• They can not survive freezing. After one day in 20 oC, they are all dead

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

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

Nematodes in cod 1973-1996

0

2

4

6

8

10

12

1973 1980 1985 1990 1996

Year

Nu

mb

er o

f nem

ato

des

Sealworm

Whaleworm

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