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Listen to this siteWednesday 19 October 2005
This research project aims to advance understanding of anisakine nematode infections of key Scottish white fish species, and to determine the efficiency of the methods currently used for detecting and removing this parasite during processing.
Study Duration : July 2005 to November 2007
Contractor : Institute of Aquaculture, University of Stirling
Anisakiasis is a potentially fatal condition associated with the accidental ingestion by humans of nematodes in infected fish. Most anisakiasis is associated with ingestion of the nematode Anisakis spp with the remainder principally associated with the related Pseudoterranova spp. This project was concerned with surveying the prevalence and intensity of infection of these nematodes in targeted Scottish white fish populations and investigating the efficacy of current processing and detection methods.
A programme of sampling was conducted for monkfish, cod, mackerel and herring fish species. Nematodes from captured fish were removed, quantified and identified with various host and parasite data recorded. The efficacy of the detection methods (visual inspection, candling, slicing, acid-digestion and pressing) was examined. Data was assessed using univariate and multivariate statistical methods, in order to examine factors affecting infection variability.
Monkfish, cod , herring and mackerel were caught from the N. Sea and waters to the W. and N. of Scotland and examined for the presence of larval anisakids in the flesh. Fish were examined by a variety of methods including, candling and slicing, digestion and pressing. Two species of nematode, Anisakis simplex and Pseudoterranova decipiens were found in the flesh of monkfish and cod, but only A. simplex occurred in the flesh of herring and mackerel.
The overall prevalence (percentage of total fish sampled found to be infected by worms) of A. simplex and P. decipiens in monkfish were 26.7% and 36% respectively, while in cod the prevelance of A. simplex was found to be 50.3% and P. decipiens 37.9%. In herring the overall prevalence of A. simplex was 36% and in mackerel 22.9%. In all fish species numbers of both A. simplex and P. decipiens increased with length of the host.
In all species of fish examined, significantly more A. simplex were found in the belly flaps than in the fillets in all fish species. In monkfish, P. decipiens was significantly more abundant in the fillets compared to the belly flaps but there was no difference between numbers of this parasite in belly flaps and fillets in cod.
A comparison of the efficacy of detection methods showed that visual inspection and candling of fillets detected only approximately 50% of the numbers of parasites detected by both candling and destructive slicing when used for monkfish and cod. In monkfish candling was only effective in fillets of up to 2.5 cm in thickness, after which the fillets were too dense for the candling light to be effective. Visual inspection and candling were more effective in detecting worms in belly flaps recovering at least 75% of the numbers found by candling and slicing. In herring and mackerel it was found there was no significant difference in the numbers of A. simplex recovered by digestion and pressing.
Sample numbers of fish required to detect single infected fish from populations with different prevalences of infection were determined taking in to account the sensitivity of each of the detection methods. It was found that the numbers of fish which need to be sampled decreases with increasing prevalence of infection.
Monkfish, cod , herring and mackerel were caught from waters surrounding Scotland and examined for the presence of Anisakis simplex and Psuedoterranova decipiens in the flesh by a variety of methods. Both species were found in the flesh of monkfish and cod, but only A. simplex occurred in the flesh of herring and mackerel. The prevalence of A. simplex was greatest in cod and lowest in mackerel. For monkfish, candling was only effective in fillets of up to a certain thickness and slicing was the most effective method for both monkfish and cod.
A full version of the report can be found (External) here on Foodbase.
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