Anisakis spp. larvae (Nematoda: Anisakidae) from Atlantic horse mackerel: their genetic identification and use as biological tags for host stock identification

In the present study, data are reported on the use of Anisakis spp. larvae, genetically identified to species level, for stock identification of Atlantic horse mackerel, Trachurus trachurus, throughout its range. Genetic markers applied to 2200 Anisakis larvae, allowed the detection of Anisakis simplex (s.s.), Anisakis pegreffii, Anisakis physeteris, Anisakis typica and Anisakis sp., in 20 horse mackerel samples. The two most dominant species were A. pegreffii and A. simplex (s.s.), with statistically significant differences between samples. A. simplex (s.s.) was the most common species found in all samples from NE Atlantic waters, with its relative proportion decreasing from north (south coast of Norway) to south (Portuguese coast off Algarve). In contrast, A. pegreffii was the most prevalent species in the Mediterranean Sea. Mixed infections of A. simplex (s.s.) and A. pegreffii were found in all samples from the Portuguese and Spanish Atlantic coasts and in a sample from south of Ireland. Finally, in horse mackerel caught off Malaga (Mediterranean Sea), mixed infections of the same two species were found in almost equal proportions. Anisakis physeteris occurred rarely and in mixed infections with A. pegreffii in a sample from the Tyrrhenian Sea. Similarly, A. typica was rarely found in mixed infections with A. pegreffii in the eastern Mediterranean (Aegean Sea), as well as the Anisakis sp. with A. simplex (s.s.) in the North Sea samples. The biogeographical pattern of Anisakis spp. larvae indicates the presence of distinct Mediterranean and Atlantic stocks of horse mackerel and supports the existence of a "northern" stock separated from a "southern" one in the Atlantic region. The results also highlight the vagility of horse mackerel, supporting the hypothesis of some migration from the Atlantic into the extreme Western Mediterranean Sea