Results and discussion

The specimen measured 66.1 mm total length (TL), 53.2 mm standard length (SL), 20 mm preanal length (PL) and its total weight was 0.810 g. It had an eel-like elongated and gelatinous body, with a rounded section, which compressed laterally towards the tail. The body was a translucent, gray-colour with violet hues, which darkened to almost black on the back, on the tip of the tail, snout, and chin. The body lateral line and scales were absent and the eyes were large and round (Figure 2). The internal organs and myomeres were visible and the number of myomeres counted was 95, within the range reported for the species (i.e. 93–99; Orlovskaya and Balushkin, Reference Orlovskaya and Balushkin2019). Five suborbitals pores and there another five mandibular ones were present under the eyes and in the lower jaw respectively, in agreement with the species' original description (Koefoed, Reference Koefoed1952). The head was ovoid and wide, 13% of total length. The pectoral fins (7 rays) were developed, while the pelvic fins were absent. The dorsal and anal fins met at the back of the body and were joined by the tail fin (Figure 2).

Figure 2. The specimen of Melanostigma atlanticum from the Sea of Crete (Total length: 66.1 mm).

Melanostigma atlanticum is the only zoarcid present in the Mediterranean (Dallarés et al., Reference Dallarés, Cartes and Carrassón2021). The specimen matched the description of M. atlanticum provided by Orlovskaya and Balushkin (Reference Orlovskaya and Balushkin2019) and differed from M. thallassium, the only Melanostigma species found in the east (but south) Atlantic and which has a non-transparent body (Orlovskaya and Balushkin, Reference Orlovskaya and Balushkin2019). The specimen is stored in formalin at the labs of the Institute of Marine Biological Resources and Inland Waters (IMBRIW, Athens, Greece).

Although several studies on fish communities have been performed in the eastern Mediterranean, this species had never been caught or reported from this region due to its deepwater habitat (Golani et al., Reference Golani, Ozturk and Basusta2006; Papaconstantinou, Reference Papaconstantinou2014). The presence of M. atlanticum in the eastern part of the Mediterranean Sea proves that the geographical distribution of the species is not restricted to the western part but spreads throughout the basin. We hypothesize that this species is native to deepwater habitats in the eastern Mediterranean, though it may be rare in these waters. The lack of earlier recording of the species in the eastern Mediterranean Sea is likely attributed to its very small size and slender body shape, which helps it easily escape capture by most commercial fishing gears, as well as the limited trawling activity at depths greater than 400 m (Maina et al., Reference Maina, Kavadas, Damalas, Pantazi and Katsanevakis2018). A large number of studies on the fish fauna of the Mediterranean Sea have concentrated in coastal areas and shallower waters, and focused mainly on commercial species, and more extensive research surveys in those deeper areas occupied by meso- and bathypelagic fish fauna will be required to better understand the biodiversity and ecology of the Mediterranean deep-sea fish community (Tsagarakis et al., Reference Tsagarakis, Darmanin, Mabruk, Auriemma, Azzurro, Badouvas, Bakiu, Bariche, Battaglia, Betti, Borme, Cacciamani, Cali, Corsini-Foka, Crocetta, Dalyan, Deidun, Digenis, Domenichetti, Dragičević, Dulčić, Durucan, Guy-Haim, Kesici, Lardi, Manitaras, Michailidis, Piraino, Rizgalla, Siapatis, Soldo, Stipa, Kurt, Tiralongo, Tsiamis, Vella, Vella, Zava and Gerovasileiou2021).