Farmed rainbow trout (Oncorhynchus mykiss) in Norway are at low risk of carrying anisakid nematodes

ABSTRACT

In total, 1038 farmed rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), were examined for the presence of nematodes between August 2015 and December 2016. The fish originated from 15 farms in western and northern Norway. Samplings took place at processing facilities and consisted of trout bound for human consumption (n = 860), and discarded fish (n = 178 incl. runts and fish discarded for other quality defects). No nematodes were found in harvest-quality rainbow trout. The only nematode findings were from five runts (loser fish) farmed in western or northern Norway. One and three runts from western and northern Norway, respectively, carried a few adult Hysterothylacium aduncum (Rudolphi, 1802) while two runts from northern Norway carried one and three Anisakis simplex (s.s.) larvae in the fillets. Findings indicate that nematode infections in farmed Norwegian rainbow trout are restricted to runts. Thus, the results suggest that the probability of nematodes to occur in the flesh of farmed Norwegian rainbow trout is very low.

KEYWORDS:

• Farmed rainbow trout
• Oncorhynchus mykiss
• survey
• Anisakis
• Hysterothylacium
• absence

Acknowledgments

We thank Mrs. Anne Margrethe Aase, Mrs. Aina Bruvik, Mr. Vidar Fauskanger and Mr. Nawaraj Gautam at the IMR’s sample reception lab., for their dedicated and skilled efforts during processing and analyses of the samples. Further, we would like to thank Mrs. Natalia Larsen for running the molecular identification analyses of the nematode species, and Dr Sylvia Frantzen for her assistance preparing the map.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was financed by the Norwegian Seafood Research Fund (FHF, project no. 901045; www.fhf.no/).