Spatial variability of helminth parasites and evidence for stock discrimination in the round sardinella, Sardinella aurita (Valenciennes, 1847), off the coast of Tunisia

Abstract Three digeneans – Parahemiurus merus (Linton, 1910), Aphanurus stossichii (Monticelli, 1891) and Lecithochirium sp. – and one tetraphyllidean cestode larva were used as biological tags to discriminate the stock of Sardinella aurita (Valenciennes, 1847). In total, 579 fish were examined in five zones off the Tunisian coast, including Bizerte and Kelibia in the north, Mahdia in the east, Gabes and Zarzis in the south. Discriminant analyses used for the separation of S. aurita allowed for the identification of two discrete stocks. Sardinella aurita from Bizerte, Kelibia and Zarzis clumped together as a single stock. Parahemiurus merus and A. stossichii were the most important species in determining the location of sampled fish from these regions. Specimens from Mahdia and Gabes were grouped as one stock characterized by the presence of Lecithochirium sp. and larvae of the Tetraphyllidea. These results were corroborated by comparing the parameters of prevalence and mean abundance of parasites among zones. The separation of S. aurita between localities after pooling specimens from Bizerte, Kelibia and Zarzis and separately pooling those from Mahdia and Gabes also allowed the identification of two discrete stocks, one in offshore waters from Bizerte, Kelibia and Zarzis characterized by the digeneans P. merus and A. stossichii and one in inshore waters from Mahdia and Gabes characterized by Lechithochirium sp. and tetraphyllidean larvae.