Presence of the bluntnose sixgill shark Hexanchus griseus (Chondrichthyes, Hexanchidae) in patagonian waters with comments on the stomach contents and reproductive condition

COSCARELLA, MARIANO ALBERTO; GARCÍA NÉSTOR ANÍBAL; CRESPO ENRIQUE ALBERTO; MARIOTTI PABLO ARIEL; KOEN-ALONSO MARIANO; DANS SILVANA LAURA

NEOTROPICA

SOCIEDAD ZOOLÓGICA DEL PLATA

Lugar: La Plata; Año: 1997 vol. 43 p. 109 - 110

0548-1686

Hexanchus griseus (Bonnaterre, 1788) is a species of the family Hexanchidae, commonly known as the bluntnose sixgill shark and widely distributed in coastal waters worldwide. In the southwestern Atlantic Ocean it was recorded for southern Brazilian and northern Argentinean waters (Compagno, 1984, FAO Fish. Synop., 125 4 0): 249). The species was previously mentioned by Menni et a/, 0 984, Peces marinos de Argentina y Uruguay, Hemisferio Sur, 359 p.) from an original record quoted by Lahille (1906, An. Minist. Agríc., 3 (1): 1-212) in a fishery bulletin, referred to a specimen caught at Miramar (Buenos Aires Province). No other information was given on the subject. The objective of this note is to document the finding of a male and a female specimens of H. griseus caught off the coasts of Patagonia, in southern Argentinean waters. The male specimen was caught by a bottom trawler vessel fishing for hake at Golfo San Jorge (46" 20' S, 66° 20' W) in May 1996, while the female was caught under similar conditions in the same area ( 45" 20' S, 64° 20' W) exactly one year later. Both individuals were brought back to port by fishermen of the company ALPESCA S. A., preserved with ice on board, and landed at Puerto Madryn, Chubut, few clays after capture. Measurements and weight of thespecimens were taken according to Compagno (op. cit.), and stomach content and gonads were analyzed. The stomach contents of the male were composed mainly by digested cephalopods and its total weight was 598 g. One lower and two upper beaks of the red octopus Enteroctopus megalocyathus were found, as well as valves of the scallop Zigochlamis patagonica and the nipper of a crustacean (presumably Eurypodiuslatreillei). A nematode was found in the stomach, and it was not attached to the organ's wall. The female stomach contents weighted 319 g, containing a digested Callorhynchus callorhynchus. Only a part of the spinal cord of the fish was preserved, weighting 10 g. A total of 8 cestodes were found in the stomach. The sexual maturity of the first specimen was determined by means of examination of the hardness of the claspers, histological samples of the testicles and epididymis smears (Pratt, 1979, Fish. Bull., 77 (2): 445-470; Brick Peres and Vooren, 1991, Fisb. Bull., 89: 655-667). The claspers were lightly calcified and no spermatozoa were found, therefore the specimen was immature. The sexual maturity of the female was determined by measuring the size of the ovocites. lt presented 6 ovocites in the right ovary (x= 0.523 ± 0.110 cm) ancl 5 ovocites in the ldt onc (x= 0.589 ± 0.174 cm). Given the state of development of the uterus, the maturity length given by Compagno (op. cit,J for females of the species and the size of the ovocites, the specimen was classified as immature. These are the second and third reports for H griseus off Argentinean waters, based on the preservation of the whole body. The finding of 1996 enlarges the distribution range for the species in over 1000 km, standing as the southernmost record in the southwestern Atlantic