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Prosjektnummer: 901543
Status: Avsluttet
Startdato: 15.03.2019
Sluttdato: 01.01.2020

Økt kunnskap om Hysterothylacium aduncum i torsk, sei og hyse norske farvann med praktiske preventive tiltak

Frembragt kunnskap om forekomst og tiltak for fjerning som kan redusere parasittforekomst på fisken
Main findings
Hysterothylacium aduncum is very prevalent and can be very abundant in cod, saithe and haddock.
H. aduncum is not present in fillets.
• The parasite is much more abundant during winter and early spring than in late spring in West-Finnmark, and this appears to be linked to an intense feeding period on spawning capelin.
• The parasite can be removed by evisceration, beheading and flushing carefully the fish at processing plants. As an alternative, apart from evisceration and flushing with water the fish body, a thorough cleaning and completely removal of the head cavities (i.e. the gill/pharynx region) may be considered.

Hysterothylacium aduncum er veldig utbredt og kan forekomme i stort antall hos torsk, sei og hyse.
H. aduncum forekommer ikke i fiskekjøttet.
• Parasitten opptrer i større mengder om vinteren og tidlig på våren enn på sen vår i Vest-Finnmark, som ser ut til å være knyttet til torskens intense beiting på gytende lodde.
• Parasitten kan fjernes ved sløying, hodekapping og grundig spyling av hele fisken før pakking. Som et alternativ kan i tillegg til nøye sløying og spyling, vurderes fullstendig fjerning av gjellene fulgt av spyling av svelgområdet.
Results achieved
Summary of results from the project’s final reporting
The fish parasitic nematode Hysterothylacium aduncum can be very abundant within the digestive tract of cod, saithe and haddock, however it is not present in the fillets. Season appears to be the most important factor explaining H. aduncum abundance in whitefish, with more parasites during winter and early spring and less parasites during late summer. It is hypothesized that whitefish may gain the maximum load of parasites through predation of spawning capelin during winter and spring in western Finnmark, since the later is known to be a host of H. aduncum. The parasite can survive for long periods in cold and humid conditions, and therefore being alive (if present in the fish lots) and actively moving when arriving at destination point. H. aduncum can be eliminated if fishes are eviscerated, beheaded and rinsed carefully at plants. Alternatively, apart from evisceration and flushing with water the fish body, a thorough cleaning and completely removal of the head cavities (i.e. the gill/pharynx region) may be considered.

Sammendrag av resultater fra prosjektets faglige sluttrapport
​Den parasittiske nematoden Hysterothylacium aduncum kan forekomme i stort antall i fordøyelseskanalen hos torsk, sei og hyse, men den forekommer ikke i filetene. Fangstsesong ser ut til å være den viktigste enkeltfaktoren som forklarer infeksjonsdynamikken til H. aduncum i hvitfisk, med flere parasitter om vinteren og tidlig på våren, og mindre parasitter på sensommeren. Det antas at hvitfisk kan få maksimal parasittbyrde ved å beite på gytevandrende lodde om vinteren og tidlig vår langs kysten av Vest-Finnmark. Parasitten kan overleve i lange perioder under kjølige og fuktige forhold, og derfor være i live og aktive når forsendelser med fersk torsk ankommer bestemmelsesstedet. Problemet med H. aduncum kan imidlertid elimineres ved at fisken hodekappes og sløyes nøye, fulgt av grundig spyling før pakking. Alternativt, i tilfeller der hode skal være på, kan man i tillegg til sløying og spyling med vann, fjerne gjellene fulgt av grundig spyling av svelgområdet. 
​Parasitten som deler av året opptrer i større mengder kan med riktige tiltak fjernes fra fisken før den eksporteres. FHF vil bidra til å formidle denne kunnskapen gjennom spredning av sluttrapport og faktaark, samt foredrag fra HI på FHF-samlinger for hvitfisknæringen.

Gjennom FHFs fokus på å øke kunnskapen om kveis i hvitfisk har FHF også iverksatt prosjektet “Kommersiell kveisdeteksjon på hvitfisk” (FHF-901614). Her er målsetningen å videreutvikle hyperspektral avbildning og fluorescens for automatisk påvisning av synlig kveis i filet, flekket fisk og saltfisk/klippfisk av fryst/tint og fersk hvitfisk. Videre har FHF utlyst midler til å kartlegge forekomst av kveis hos hvitfisk i norske farvann. Denne kartleggingen kan komme i gang høsten 2020.
The larvae of parasitic nematodes, particularly Anisakis, Pseudoterranova and Contracaecum species, in Norway collectively known as “kveis”, commonly occur in the viscera and muscle of many commercially important marine fish species, such as cod (Gadus morhua), saithe (Pollachius virens) and haddock (Melanogrammus aegleginus). These parasites may cause human disease (anisakidosis) upon consumption of raw, marinated or lightly processed fishery products contaminated with viable larvae. Kveis are also of socioeconomic concern, since they may reduce the marketability of fishery products and cause rejection of products by sellers and consumers.

Another “kveis”-type, Hysterothylacium aduncum, is also very common in gadoid whitefish caught in Norway. In contrast to Anisakis which use marine mammals (cetaceans) as final host, Hysterothylacium lives exclusively in cold-blooded organisms (marine invertebrates and fish) and is per definition not adapted to the conditions that prevail in the alimentary tract of mammals. Therefore, H. aduncum is considered non-zoonotic, i.e. in principle, it does not pose any direct consumer health risk. However, H. aduncum can indeed heavily infect some fish species, and the massive presence of larval or adult specimens in or around the visceral organs could contribute to a reduction of the aesthetical appeal of the products, potentially causing socioeconomic problems to the industry. 
• To improve our knowledge in relation to the timely and spatial occurrence and distribution of Hysterothylacium aduncum in cod, saithe and haddock caught in Norwegian waters.
• To study current handling procedures along the fish value chain, as a basis for advice to improve handling/cleaning practices in processing plants.
• ​To assess survival and motility of the parasite by mimicking the temperature conditions during handling and transport of fresh cod to European markets. 
Expected project impact
Based on the results and findings of this project, the industry will be advised with respect to revising their handling practices in order to improve parasite control measures adapted to fish species, fishing ground, catching date and handling, etc. If implemented by the industry, the recommendations could largely eliminate the problems at the marketplaces caused by Hysterothylacium.
Project design and implementation
Fish sampling

30 cods will be sampled freshly on board a fishing vessel by HI (IMR) researchers and visually inspected for Hysterothylacium. Whole catches will be followed throughout the production chain from catch via landing and processing to final packing in the plant, in order to identify critical control points for the detection and subsequent elimination or at least drastic reduction of the Hysterothylacium problem. Additionally, 30 saithe and 30 haddock fished in March 2019, and the same numbers of fish (i.e. 30 cod, 30 saithe and 30 haddock) caught in April/May 2019 in the Barents Sea, need to be frozen as soon as possible after capture (if not possible, cooling conditions must be kept from the boat to IMR facilities), and sent to the IMR for parasite inspection and identification. 

Hysterothylacium survival trials
Hysterothylacium will be collected from cod viscera and placed in petri dishes in physiological saline which will be kept in a fridge at 2–4⁰C for at least 7 days, thus mimicking the temperature conditions during transport to various markets. Hysterothylacium will be also placed in a peptic solution, which mimics the conditions found in the mammalian stomach. Hysterothylacium survival will be assessed in both trials. Results might provide some valuable information to determine if Hysterothylacium would survive long enough in order to eventually be able to cause any damage in a human stomach.

Data analyses and reporting
Parasite data will be analyzed, and descriptive infection data such as prevalence and abundance per infection site/organ will be calculated. The relationship between nematode abundance and fish size and sex will be statistically assessed. Based on the results of the observations and analyses, a set of guidelines will be prepared, e.g. a visual flow chart, so that the industry can implement certain handling and cleaning routines during processing of fresh cod/whitefish in order to cope with the Hysterothylacium problem.​ 
Dissemination of project results
It is planned to publish an article in the IMR's website and in a peer-reviewed international scientific journal.

A workshop on the “kveis”​-problem in the Norwegian whitefish industry will be organized at the IMR in Bergen during autumn 2019. As a synergistic spin-off effect, the results and findings from the currently proposed project on Hysterothylacium, will be also integrated in the workshop.