Helminth parasites of the chub mackerel Scomber colias off the Tunisian coast and their use in stock discrimination.

ABSTRACT

Nine helminth parasites were used as biological tags to discriminate diverse areas of Scomber colias Gmelin, 1789. During three seasons, a total of 369 fish were examined in four zones off the Tunisian coast, including Bizerte in the north, Kelibia and Mahdia in the centre and Zarzis in the south. Discriminant analyses were used to identify distinct areas of S. colias. Fish from Bizerte were grouped as one area and were correlated negatively with the monogenean Grubea cochlear and the digenean Lecithocladium excisum. Specimens from Kelibia and Mahdia were grouped together and were characterized by the ectoparasite Pseudokuhnia minor and by endoparasites Prodistomum orientalis, Monascus filiformis and anisakid larvae. Fish from Zarzis were grouped as one area and were positively correlated with the monogenean G. cochlear and the digenean L. excisum. These results were corroborated by comparing the prevalence and mean abundance of parasites among zones. Results of other discriminant analyses used for the classification of S. colias between localities after pooling specimens from the central areas of Kelibia and Mahdia also allowed the identification of three distinct areas one in the north, correlated negatively with G. cochlear and L. excisum; one in the centre, characterized by P. minor, P. orientalis, M. filiformis and anisakid larvae; and one in the south, from Zarzis, characterized by G. cochlear and L. excisum. Results of comparisons of infection parameters between seasons and those of seasonal discrminant analyses showed a seasonal stability of communities from the northern and the southern areas. Specimens from the central regions showed variability between seasons, suggesting migratory movements.