1 Historical records and new occurrence of the rare serpent eel Ophisurus serpens 2 (Linnaeus, 1758) in the Mediterranean Sea 3 4 Vasiliki Kousteni*and George Christidis 5 6 Institute of Marine Biological Resources and Inland Waters, Hellenic Centre for Marine 7 Research, 46.7 km Athens Sounio ave., P.O. Box 712, 19013 Anavyssos Attiki, Greece 8 *Corresponding author. Email: [email protected], Tel.: +302109856714 9 10 Abstract 11 A specimen of the serpent eel Ophisurus serpens (Order: Anguilliformes, Family: 12 Ophichthinae) reaching 2100 mm in total length was caught on 13 October 2017 by bottom 13 trawl at mean depth 206.5 m in Saronikos Gulf (central Aegean Sea, Greece). This specimen 14 is the second record in this area since 1979 and the largest specimen ever recorded in the eastern 15 Mediterranean Sea. Historical records of this rare species in the Mediterranean Sea are reported 16 and discussed. 17 18 Keywords: Ophisurus serpens; new record; Saronikos Gulf; eastern Mediterranean Sea 19 20 Introduction 21 The family Ophichthidae consists of 59 genera with about 290 species, from which only 8 have 22 been reported in the Mediterranean (Filiz et al., 2015). The serpent eel Ophisurus serpens 23 (Linnaeus, 1758) is a marine, brackish, reef-associated and benthic species living in sandy and 24 sandy-muddy bottoms up to 300 m in depth (Bauchot, 1986). It is widely distributed in the 25 eastern Atlantic (northern coast of the Iberian Peninsula to South Africa, including Madeira), 1 26 in the western Indian Ocean (Southern Mozambique to South Africa), and in the western 27 Pacific (Japan and Australasia) (Bauchot, 1986), although the western Pacific populations are 28 thought to belong to a co-generic species (Nakabo, 2002). Its first bibliographic record in the 29 eastern Atlantic dates back to 1866 and comes from the Galician waters (López-Seoane, 1866), 30 while after about 100 yrs it is reported for the first time in the western and central 31 Mediterranean (Dieuzeide, 1954; Lubet and Azzouz, 1969; Tortonese, 1970; Bauchot, 1986). 32 More recent records in this basin refer to: the Alboran Sea (Abad et al., 2007), the Ligurian Sea 33 (Relini et al., 2007), the Tuscan and Latium coasts of Italy (Biagi et al., 2002), the Tunisian 34 waters (Ben Amor et al., 2009, 2017; Rafrafi Nouira et al.,2015), the Adriatic Sea (Jardas, 35 1996; Dulcic et al., 2005; Bettoso and Comisso, 2015), the Ionian Sea (Maiorano et al., 2010), 36 and the Libyan coast (Al Hassan and El Silini, 1999; Shakman and Kinzelbach, 2007). In the 37 eastern Mediterranean, O. serpens has been recorded 8 times the last 50 yrs off the Turkish 38 coasts (Geldiay and Mater, 1968; Karakulak et al., 2006; Sangun et al., 2007; Cengiz et al., 39 2011; Filiz et al., 2015; Torcu Koç and Erdogan, 2015; Ulaş and Akyol, 2015; Erguden et al., 40 2016), while one record comes from Egypt (El Sayed, 1994) and only two records come from 41 the eastern Levantine (Golani, 1996; Dalianis et al., 2016). In the Greek waters, the species has 42 been reported only 4 times since its first record dated to 1973 in Korinthiakos Gulf (Kaspiris, 43 1973). The other Greek records include: the Ionian Sea (Kaspiris, 1984), the Evoikos Gulf 44 (Papaconstantinou et al., 1994; Stergiou et al., 1997), and the Saronikos Gulf 45 (Papaconstantinou and Tsimenidis, 1979). 46 47 Materials and methods 48 On 13 October 2017, one mature female O. serpens was captured by trawl between 49 37°51′10.8″N–37°52′12″N and 23°11′20.4″E–23°14′11.76″E in the Saronikos Gulf, at depths 50 between 200–213 m (Fig. 1). The field sampling was conducted in the frame of a research 2 51 programme (MINOUW) using the experimental bottom trawling vessel R/V Filia (HCMR) 52 equipped with a bottom trawl net of 22 mm square-mesh codend size. The haul duration was 53 61 min and the haul speed was set at 2.4 knots. Morphometric measurements were obtained 54 with digital calipers to the nearest 0.01 mm. Meristic characteristics included counts of fin rays 55 in dorsal, pectoral and anal fins, and counts of pores in the lateral line canal system and the 56 canals located on the head (ethmoid, infraorbital, supraorbital, preoperculo-mandibular and 57 supratemporal). Total weight, eviscerated weight, liver and gonad weight were recorded in 58 grammes. The specimen was preserved in 10% formalin and deposited in the Institute of 59 Marine Biological Resources and Inland Waters (HCMR, Athens, Greece; Catalogue number: 60 HCMR OS01). The historical and present records of O. serpens in the Mediterranean were 61 mapped using the GIS software ArcView v10.4. 62 63 Results and Discussion 64 The historical and present records of the serpent eel Ophisurus serpens in the Mediterranean 65 Sea (Fig. 2) confirm the presence of the species in the whole basin with 17 records reported 66 either in the western-central part or in the eastern part. The present study reports a new record 67 of the species in the Saronikos Gulf (central Aegean Sea) where it was first reported 40 years 68 ago. 69 Ophisurus serpens was captured by bottom trawl in a sandy-muddy bottom, a habitat 70 where it is commonly found as supported by previous studies (e.g. Filiz et al., 2015; Ulaş and 71 Akyol, 2015). The mean depth of capture (206.5 m) was in the range of previously reported 72 depths where this species was found (Table I). With special regard to maximum body size, 73 Bauchot (1986) reported the largest specimen in the Mediterranean Sea reaching 2400 mm in 74 TL. The present study reports the largest specimen (2100 mm in TL) recorded in the eastern 3 75 Mediterranean (Table 1), where the previously recorded largest specimen reached 2000 mm in 76 TL (Torcu Koç and Erdogan, 2015). 77 Morphometrics and meristics are in agreement with previous descriptions of the species 78 (Table 2). The species is characterized by elongated, cylindrical and scaleless body, relatively 79 small eyes, slender and conical snout with the upper jaw projecting, and elongate jaws that 80 extend posteriorly beyond the eye. It has large caniniform and curved teeth on premaxillae, 81 small and biserial teeth on maxillae, small and uniserial teeth on lower jaw, as well as uniserial 82 and enlarged anteriorly vomerine teeth. The dorsal, pectoral and anal fins are well developed, 83 while pelvic and caudal fins are absent. The origin of the dorsal fin is slightly posteriorly to the 84 pectoral fin and the anus is located in the anterior half of the body. Concerning coloration, the 85 body is brownish-olive dorsally, silvery with yellow iridescences ventrally, both dorsal and 86 anal fins have grey edges, and the pores are blackish. The observed number of pores in the 87 lateral line reach 200. In previous studies, the number of pores in the lateral line ranged between 88 149 in a small specimen reaching 333 mm in TL (Ben Amor et al., 2009) and 206 in a larger 89 specimen reaching 2000 mm in TL (Torcu Koç & Erdogan, 2015). A positive and significant 90 relationship was observed between the number of pores in the lateral line with body size (ln(α) 91 = 4.0684, b = 0.1634, R2 = 92.5, P-value = 0, N = 10) (Fig. 3). 92 Although Saronikos Gulf is one of the best monitored and studied marine areas in 93 Greece with a variety of fisheries taking place in the area (Karlou-Riga and Vrantzas, 2001), 94 no previous record of O. serpens has been reported, except that by Papaconstantinou and 95 Tsimenidis (1979). This supports the conclusion of the rarity of the species in this area. 96 However, no safe assumption could be made given the fact that the serpent eel has an extremely 97 elongate and cylindrical body and lives buried with only its head exposed (Jardas, 1996) that 98 makes it difficult to capture. Moreover, it has no commercial value and is likely discarded by 99 fishermen. Consequently, the species might be less rare than thought and its presence is 4 100 probably underestimated. A targeted survey could better assess the effective presence and 101 abundance of O. serpens in the Saronikos Gulf and check the establishment of the species in 102 the area. 103 104 Acknowledgements: The field sampling was funded by the European Commission’s Horizon 105 2020 Research and Innovation Programme under Grant Agreement No. 634495 for the project 106 Science, Technology, and Society Initiative to minimize Unwanted Catches in European 107 Fisheries (MINOUW). 108 109 Conflict of Interest: The authors declare that they have no conflict of interest. 110 111 Ethical Approval: This article does not contain any experimental studies with animals 112 performed by any of the authors. 113 114 References 115 Abad, E., Preciado, I., Serrano, A., Baro, J., 2007. Demersal and epibenthic assemblages of 116 trawlable grounds in the northern Alboran Sea (western Mediterranean). Sci. Mar. 7, 117 513–524. DOI: 10.3989/scimar.2007.71n3513. 118 Al-Hassan, L.A.J, El-Silini, O.A., 1999. 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