In the present study, data on the presence, parasitological indices of Anisakis larvae, and molecular identification of A. pegreffii, A. typica, A. ziphidarum, and A. simplex (s.s.)/A.pegreffii hybrid in S. scrofa from the Aegean Sea (Eastern Mediterranean Sea, FAO 37.3.1) are presented. The results present the first molecular detection of A. typica and A. ziphidarum in S. scrofa, and thus this fish species is a new host for two Anisakis species. This is also the first comprehensive survey on the Anisakis parasites of S. scrofa in the Mediterranean Sea (Table 1).
Anisakis type I (sensu Berland 1961) and type II (sensu Berland 1961) larvae have been previously reported from S. scrofa in the western Mediterranean Sea (Petter and Maillard 1988). In the Northeast Atlantic Ocean (Galician waters, Northwest Spain), Abollo et al. (2001) reported 100% prevalence of Anisakis larvae in S. scrofa, and A. pegreffii and A. simplex (s.s) species were genetically identified. The presence of Anisakis spp. in S. scrofa was detected as 27% (3/11) in the Western Mediterranean Sea (FAO 37.1.3) (Ferrantelli et al. 2015). Recently, Costa et al. (2018) recorded a high prevalence (P = 50%, 4/8) of A. pegreffii in S. scrofa from the Ionian Sea (FAO 37.2.2) and the Eastern Mediterranean Sea (FAO 37.3). The overall prevalence of Anisakis larvae in S. scrofa in the present study (P = 9.6%, 26/272) was lower than those studies in the same host species sampling from the Mediterranean Sea and the NE Atlantic Ocean (Abollo et al. 2001; Costa et al. 2018; Ferrantelli et al. 2015). Since the overall sample size of these previous studies on Anisakis spp. infecting S. scrofa were considerably lower compared to our study, it is possible that their prevalence of Anisakis larvae may have been detected at relatively higher rates. In fact, relatively high rates of Anisakis prevalence could be affected by the small sample size (Farjallah et al. 2008; Pekmezci et al. 2014; Pulleiro-Potel et al. 2015; Serracca et al. 2013). Moreover, a sample size of more than 15 specimens is enough to obtain a good estimate of prevalence (Jovani and Tella 2006).
Anisakis pegreffii is the dominant species in the Mediterranean Sea (Mattiucci et al. 2013; 2017; 2018). In the present study, 51.3% of all larvae collected from S. scrofa were genetically identified as A. pegreffii. This molecular finding confirmed A. pegreffii as the dominant species in the Mediterranean Sea. To date, there are still insufficient data on the presence of A. ziphidarum larvae in fish species caught in the Mediterranean Sea (Mattiucci et al. 2018). Anisakis ziphidarum larvae have been previously detected in Diaphus metopoclampus, Lepidopus caudatus, Merluccius merluccius, and Xiphias gladius from the Alborean, the Balearic, the Crete, the Ionian, the Ligurian, and the Tyrrhenian Sea (Gaglio et al. 2018; Mattiucci et al. 2007). The S. scrofa in the present study is a new intermediate/paratenic host record for A. ziphidarum. In addition, A. ziphidarum is reported for the first time in the Aegean Sea, providing a new geographical record for this species. Anisakis typica occurs in warm temperate and tropical waters between 35‒40° N and 36° S (Mattiucci et al. 2018), and it has been often reported from M. merluccius, Micromesistius poutassou, Phycis phycis, Scomber japonicus, S. scombrus, and Trachurus trachurus (Farjallah et al. 2008; Mattiucci et al. 2002, 2004, 2008; Pekmezci et al. 2014) in the Mediterranean Sea. The spread of A. typica to the Mediterranean Sea has been related to the lessepsian migration of its paratenic/intermediate hosts from the Indian Ocean (Mattiucci et al. 2004). The present study also presents the first report of A. typica larvae in S. scrofa as a new host in the Mediterranean Sea. It is known that while A. pegreffii is dominant species in the Mediterranean Sea, A. simplex (s.s.) is dominant in the Atlantic Ocean (Mattiucci et al. 2018). In the present study, A. simplex (s.s.)/A.pegreffii hybrid in S. scrofa was identified by RFLP analysis of the ITS region previously reported Abollo et al. (2003) and D'Amelio et al. (2000). Anisakis simplex (s.s.)/A.pegreffii hybrid was also previously identified by ITS-RFLP analysis in the Aegean Sea (Chaligiannis et al. 2012; Pekmezci et al. 2014). However, ITS‒RFLP analysis could provide an overestimation of hybrid (Mattiucci et al. 2016). Recently, A. simplex (s.s.)/A.pegreffii hybrid was confirmed by the elongation factor 1 alpha 1 (EF1 α-1) nDNA gene sequencing (Mattiucci et al. 2016; Roca-Geronès et al. 2021). Although this species was identified by RFLP analysis of the ITS region, it could be confirmed by sequencing of EF1 α-1 nDNA gene in the future studies. The occurrence of A. simplex (s.s.)/A. pegreffii hybrid has been previously reported from Engraulis encrasicolus, L. caudatus, Lophius piscatorius, M. merluccius, M. poutassou, Pagellus erithrinus, Sardina pilchardus, T. picturatus, T. trachurus, T. mediterraneus, S. colias, S. japonicus, S. scombrus, and Zeus faber in the Aegean and Mediterranean Sea (Abollo et al. 2003; Cavallero et al. 2012; Chaligiannis et al. 2012; Costa et al. 2016; Farjallah et al. 2008; Gazzonis et al. 2017; Meloni et al. 2011; Molina-Fernández et al. 2018; Pekmezci et al. 2014; Roca-Geronès et al. 2021). Our findings also report the presence of A. simplex (s.s.)/A. pegreffii hybrid in S. scrofa.