Biscoito, Manuel & Saldanha, Luiz, 2018, Gaidropsarus mauli a new species of three-bearded rockling (Gadiformes, Gadidae) from the Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge) and the Biscay Slope (Northeastern Atlantic), Zootaxa 4459 (2), pp. 301-314: 303-309
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Gaidropsarus mauli n. sp.
Gaidropsarus argentatus (non Reinhardt, 1837): Quéro et al. 1993:120.
Onogadus sp.: Desbruyères et al. 1994: 19.
Gaidropsarus n. sp.: Saldanha & Biscoito, 1997: 197; Desbruyères et al. 2001a:1335, 2001b: 89.
Gaidropsarus sp.: Biscoito & Almeida 2006: 497; Cuvelier et al. 2009: 2029, 2031.
Holotype. MMF 26955, 320 mm SL, Lucky Strike hydrothermal vent site, Mid-Atlantic Ridge (37° 17’.32 N and 32° 16’.51 W), DIVA-2 cruise, NAUTILE dive No. 0 8, 1685 m, 10th June 1994.
Paratype. CFC 1992.9. 3, 300 mm TL, Blackmud Canyon , Bay of Biscay slope, ca. 47° 50’ N, 7° 40’ W, 850– 900 m. Landed on 9th September 1992 at Concarneau, France. Collected by the trawler “EUREKA”.GoogleMaps
Diagnosis. A medium-sized reddish species of Gaidropsarus with a depressed head and a blunt snout, rounded in dorsal view; head length 23.4–25.4% SL; eye small, 20.9–21.3% SL; first dorsal-fin ray short, 21.3–25.4% HL. Caudal peduncle ogee-shaped, short, slightly higher than long. Pectoral fin very broad, spatulate, length 17.8– 19.4% SL and its height 10.6–11.0% SL. Pelvic fins long, reaching to or exceeding the level of the vent, 27.5– 33.3% SL. Lateral line short, inconspicuous, present only over the pectoral and reduced to five minute segments with one pore at each end. Vertebrae 46–47 (14+32–33).
Description. Measurements, body proportions and meristic counts are given in Table 1.
Body elongate. Preanal length greater than the caudal region (from the vent level to the end of the caudal peduncle), 53.1% of SL (50.8% in the paratype). Head depressed, rounded in dorsal view. Snout blunt ( Fig. 3 View Figure ). Eyes rounded, more than twice snout length and placed in a dorso-lateral position. Nasal barbels longer than eye diameter. Chin barbel of paratype more than twice the eye diameter (deformed in holotype). Mouth rictus reaching the level of the anterior margin of the eye. Tongue free, lanceolate.
Maxilla reaching the level of posterior margin of the eye. Pelvic fin insertion anterior to upper origin of pectoral fin. Last dorsal- and anal-fin rays very close to first caudal-fin rays, not leaving any conspicuous space. Caudal peduncle ogee-shaped.
Gill rakers ( Fig. 4 View Figure ). Gill rakers sparse, tuberculate and flattened, with many prickles.
Lateralis system ( Fig. 5 View Figure ). Lateral line on body inconspicuous, reduced to five minute segments, each with a pore at each end.
Supraorbital canal with four pores: the first placed near the tip of snout, the second at base of barbel, the third beyond barbel near level of posterior nostril, and fourth near upper anterior margin of eye. Supraorbital commissure with a single pore between eyes. Temporal canal with five pores: two posterior ones placed at posterior part of head close to lateral line. Supratemporal commissure with two pores.
Infraorbital canal with twelve pores: first four pores at the anterior margin of an upper labial fold, on anteriormost portion of snout, the fifth slightly beyond the chin barbel level, eighth under the eye, 11th and 12th in a post-orbital position, 9th and 10th placed respectively over and behind end of maxilla. Supratemporal commissure with two pores. Preoperculo-mandibular canal with 13 pores (11 on the paratype): first placed on the “chin”, the fifth and sixth near posterior part of maxilla, remaining pores in a preopercular position. One more pore placed outside of preopercular row and near infero-posterior edge of opercle. This pore is lacking in the paratype.
Dentition ( Figs. 6 View Figure , 7 View Figure ). Teeth sharp and lanceolate (sometimes blunt) with a conical shape directed posteriorly on premaxillary, mandibular and vomer. Teeth on premaxillary cardiform. Mandibular with larger teeth than those on premaxillary. Vomer tooth patch V-shaped with longer teeth posteriorly, larger than those on the mandibular. When the mouth is closed the lower jaw dentition fills the space between premaxillary and the vomer dentition.
Colouration. The following description is based on the type specimen ( Fig. 2 View Figure ) and direct observations from the submersible of at least 6 individuals (see also figures in Biscoito & Almeida 2006). Red pinkish overall, colour less intense on the abdominal region, varying from more or less uniform to a mottled pattern, with darker bluish spots and silvery areas along the body and silvery areas mainly ventrally. In some specimens a whitish patch on cheek.
Habitat. Several specimens of G. mauli were observed during dives performed by the “Nautile” ( Fig. 2 View Figure ). The fishes were generally immobile in crevices along rocky walls covered by dense populations of Bathymodiolus azoricus in the vicinity of the venting fluids. A density of nearly one individual per square metre was recorded around one of the tallest chimneys, named “Eiffel Tower”. According to Cuvelier et al. (2011) water temperature measured continuously at the level of the mussel beds varied between 4.44°C and 9.54°C, with mean values of total sulphides (ΣS) varying between 0.81µm and 9.00µm and CH 4 between 4.76µm and 8.73µm. An in situ temperature measurement taken by one of us (LS) at the collecting site gave as much as 11°C.
There are no habitat data for the paratype.
Feeding habits. The stomach of the holotype (Lucky Strike) contained 11 shrimps, Mirocaris fortunata Martin & Christiansen, 1995 (Family Bresiliidae ) and remains of 5 others probably of the same species. The paratype (Bay of Biscay) had in the stomach a partially digested specimen of Cataetyx alleni (Byrne, 1906) (88 mm SL; Pisces, Bythitidae ) and remains of 3 anomuran crustaceans of the families Chyrostyllidae and Galatheidae .
As in many deep-sea fishes, G. mauli shows an opportunistic feeding behaviour, as revealed by the stomach contents of these two fishes from very different habitats. As with other fishes living in the neighbourhood of vents ( Geistdoerfer 1988; Saldanha 1994), G. mauli can feed on the abundant hydrothermal food source.
Etymology. This species is dedicated to our good friend and fine ichthyologist Günther Edmund Maul (1909̄1997), former Director of the Funchal Natural History Museum, Madeira, in recognition of his outstanding contribution to the knowledge of the Atlantic ichthyofauna.
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