First record of Thysanoteuthis rhombus (Cephalopoda: Thysanoteuthidae) in the Adriatic Sea

Abstract

The diamond-shaped squid, Thysanoteuthis rhombus Troschel, 1857 is a non-abundant epipelagic inhabitant of warm tropical and partially subtropical waters (water temperature >20 or 21°C, usually 23 to 26°C) of the World Oceans and the Mediterranean (Nigmatullin et al., 1995). The squid penetrates into the upper latitudes of subtropical and temperate waters (the Japan Sea, the waters of South Africa and America) with warm currents. It occupies near-surface waters during the night and midwaters during the day and often occurs alone or in pairs and has a life span of approximately one year (Nigmatullin et al., 1995). The most abundant populations have been found in the waters of Japan (Nishimura, 1966) where some local fisheries target this species (Bower & Myahara, 2005). This species was first described from the Strait of Messina in the Mediterranean Sea which is the type locality of T. rhombus, but it is rare here (Mangold & Boletzky, 1988). There were no records of diamond-shaped squid in the Adriatic Sea. This paper presents first record and morphometry of this species from the Adriatic Sea. A single male specimen of T. rhombus (Figure 1) was caught using a hand squid jig just after dusk on 26. December 2006, 15 meters offshore of Dolfin Islet (44°41'N 14°41'’E) at the depth of 10 m (the shallowest recorded capture of a live specimen in the Mediterranean Sea), near the islands of Rab and Pag in the eastern part of the northern Adriatic Sea. At the time of capture, the sea temperature was 12°C, and the air temperature was 15°C. The species was identified using the key in the FAO Cephalopod Catalogue (Roper et al., 1984). The specimen is archived in the malacological collection of the Rijeka Natural History Museum under inventory number PMR004979. Analysis of the individual included measurements to the nearest millimetre, body weight to the nearest gram, determination of sex and maturity stage.