First record of Melanocetus johnsoni Gunther, 1864. (Ceratoidei: Melanocetidae) in Argentina waters with a description on scales and sagittae

VOLPEDO ALEJANDRA VANINA; ECHEVERRÍA DINORAH DIANA; GARCÍA NÉSTOR ANÍBAL; CRESPO ENRIQUE ALBERTO

NEOTROPICA

SOCIEDAD ZOOLÓGICA DEL PLATA

Lugar: La Plata; Año: 1998 vol. 44 p. 117 - 118

0548-1686

The order Lophiformes comprises batipelagic fishes with wide distribution ranges (Pietsch and Groebecker, 1987; Pequeño, 1989; Kong and Melendez, 1991; Nelson, 1994). The genus Melanocetus belongs to the family Melanocetidae, and contains five species (Pietsch and van Duzer, 1980; Nelson, 1994). Pietsch and van Duzer (1980) reviewed the records of Melanocetus johnsoni which is found in tropical and subtropical latitudes of the Pacific, Atlantic and Indian Oceans, between 500 and 1500 m depth. The southernmost record of the species belongs to a specimen collected in the Pacific Ocean close to 45°S, 165°W (Pietsch and van Duzer, 1980).The aim of this note is to communicate the record of a specimen of Melanocetus johnsoni in waters of the Mar Argentino, along with some characteristics of the external morphology (Fig. 1). It was collected by the fishing vessel Othori, to the southeast of Isla de los Estados (55° 05´ S; 63° 0? W) in February, 1995. The specimen was find in a mid-water trawl fishing Patagonian grenadier (Macruronus magellanicus, Lonnberg, 1907) and southern blue whiting (Micromesistius australis, Norman, 1937) at 700 m depth. The specimen was identified by means of the key for the family (Pietsch and van Duzer ,1980), based on the following characters: number of teeth in the lower jaw (46), number of radials in the anal fin (4); pectoral fin (17); caudal fin (8). The dorsal fin was deteriorated but we counted 15 radials. The ratio between the length of the lower jaw with respect to standard length was around 1,01% (Fig. 2.A) and those features are concordant with the description of Melanocetus johnsoni from Pacific Ocean waters reported by Kong and Melendez (1991).The following measurements were also taken according to Kong and Melendez (op. cit.): standard length: 220,7 mm; orbital diameter: 4,85 mm; postorbital width: 47 mm; height of the caudal peduncle: 15,18 mm; preorbital length: 51,36 mm; postorbital length: 47 mm and head length: 105,94 mm.The specimen is an immature female. The scales are conic shaped, with a circular base and the free edge oriented to the caudal region of the fish (Fig. 2.B). They are hollow and translucent. Regarding the left otolith, it shows a general oblong shape, with regular edges, the inner face does not present rostrum, antirostrum or cisure. A straight sulcus is present, not divided in ostium and cauda and it is located in the anterior and central part of the otolith. It shows a dorsal depressed area which extends from the anterior edge of the sulcus to the posterior edge of the otolith. The external face shows a undulated surface and its width is 20% of the total length of the otolith (Fig. 2, C and D).The closest record for Melanocetus johnsoni to the Mar Argentino is located at 40° S; 47° W (Pietsch y van Duzer, 1980). The southernmost location in the southern hemisphere for this species is 40° S in the western south Atlantic Ocean, and 45° S in the Pacific Ocean (Pietsch y van Duzer, 1980). This finding is the southernmost record for the species and is the first for Argentina. The specimen is deposited in the Scientific Collection of the Laboratory of Vertebrates (LV-FCEN-UBA).