# Zoonotic nematode larvae in Greenland halibut (Reinhardtius hippoglossoides) from Greenlandic waters: Occurrence, fillet distribution and association with Mushy halibut syndrome

## TL;DR

This study found zoonotic nematode larvae in Greenland halibut, linked to a quality issue called Mushy halibut syndrome, and highlights food safety and ecosystem monitoring concerns.

## Contribution

The study is the first to investigate anisakid nematode distribution in Greenland halibut and its association with Mushy halibut syndrome.

## Key findings

- Anisakis simplex s. s. was the most common nematode species found in fillets, especially in belly flaps.
- Mushy halibut syndrome was associated with higher parasite levels in belly flaps and liver.
- Parasite presence in Greenland halibut has implications for food safety and ecosystem monitoring.

## Abstract

Zoonotic anisakid nematodes commonly infect wild fish, and their presence in commercially caught species represents a consumer hazard due to risk of anisakidosis. The Greenland halibut (GLH) is a species of high commercial value to many countries, including Kalaallit Nunaat (Greenland), where GLH is the second most exported marine species. Despite this, the occurrence of anisakid nematodes in the flesh of GLH remains poorly studied. Additionally, the relationship between anisakid infection and ‘Mushy halibut syndrome’ (MHS), a condition affecting the fillet quality of GLH, has not been investigated. The aim of this study was to extend our knowledge of the occurrence of anisakid nematodes in GLH, with emphasis on fillet distribution, and explore associations with MHS. GLH (n = 104) from three offshore fishing grounds underwent necropsy and parasitological examination of the main fillet and belly flaps. Overall prevalence of third-stage larval infection was 44.2 %, while mean intensity and abundance were 4.6 and 1.3, respectively. When examining the fillets, third-stage larvae were predominantly found in the belly flaps. For a subsample of fish (n = 55), the investigation included parasitological examination of the body cavity and liver as well as extended necropsy, quality index method assessment and age estimation. The isolated third-stage larvae belonged to three species: Anisakis simplex s. s. was most common (n = 721), followed by Contracaecum osculatum (n = 36). Phocanema bulbosa was found in the body cavity and liver only (n = 11). MHS was associated with higher infection levels in the belly flaps and liver, lower condition factor and higher gonadosomatic index. The results presented here have implications for wild fish stock monitoring and food safety. Recording of the parasite prevalence and distribution in GLH can assist risk management and provide information on the status of the fish species in the ecosystem.

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•This study mapped the distribution of anisakid larvae in Greenland halibut.•Anisakis simplex, Contracaecum osculatum and Phocanema bulbosa were identified.•A. simplex s. s. dominated in the fillet and occurred mainly in the belly flaps.•Belly flap and liver parasitism were associated with Mushy Halibut Syndrome.•Parasitological investigations support ecosystem and food safety assessments.

This study mapped the distribution of anisakid larvae in Greenland halibut.

Anisakis simplex, Contracaecum osculatum and Phocanema bulbosa were identified.

A. simplex s. s. dominated in the fillet and occurred mainly in the belly flaps.

Belly flap and liver parasitism were associated with Mushy Halibut Syndrome.

Parasitological investigations support ecosystem and food safety assessments.