Size at maturity, sexual dimorphism, gonad development, and abundance of white-dotted skate, Bathyraja albomaculata, were assessed along its geographic range in the Southwest Atlantic, from Uruguay to Tierra del Fuego (Argentina). In all, 291 specimens from eight research cruises conducted between 1998 and 2003 were examined. Length–mass relationships were sexually dimorphic, adult females being significantly heavier than males of the same length. The largest female observed was 762 mm total length (LT), and 50% maturity (LT50) was attained at 653 mm LT. The largest male was 732 mm LT, and male LT50 was 628 mm LT. Female and male LT50 were not significantly different and were about 86% of observed maximum size, similar to other Bathyraja species. The lack of sexual dimorphism in size at maturity and the slight difference in maximum size between sexes support the hypothesis of relaxation of selection for large female size in oviparous elasmobranchs. Liver size was not sexually dimorphic. Mature female gonads were symmetrical in terms of mass, and similar in ovarian follicle number and size. Females carried egg cases in April, September, and October, consistent with previous observations around the Islas Malvinas and suggesting year-round egg laying. Bathyraja albomaculata was most abundant on the outer continental shelf and slope between 36°30′S and 45°S (northern area). In contrast, it was generally absent between 48°S and 52°S (southern area), a region where it was formerly reported as abundant. These differences are coincident with the development of a fishery targeting skates in the southern area, whereas in the north B. albomaculata taken as bycatch are mostly discarded alive.

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Antarctic notothenioid fish display specializations related to cope with their chronically cold environment, such as high triacylglycerol (TAG) content in tissues. The metabolic fate of glycerol, a product of TAG mobilization, has not been studied in Antarctic fish. To assess the importance of glycerol as a substrate for gluconeogenesis and to determine whether this pathway is metabolically cold adapted (MCA), key hepatic enzyme activities were measured in Antarctic (Notothenia coriiceps, Gobionotothen gibberifrons, and Chionodraco rastrospinosus) and non-Antarctic (Dissostichus eleginoides, Patagonotothen ramsayi, and Eleginops maclovinus) notothenioid fish. Fructose 1,6-biphosphatase (FBP), phosphoenolpyruvate carboxykinase (PEPCK), and glycerol kinase (GK) activities were similar in both groups at common temperatures (1, 6, 11, or 21 °C). In particular, thermal sensitivity for the reactions catalyzed by FBP and PEPCK was analogous between Antarctic and non-Antarctic species, reflected by similar values for Arrhenius energy of activation (E a ) and Q 10 . Additionally, hepatic glycerol, glucose, and glycogen contents together with plasma glycerol and glucose concentrations were similar for all of the species studied. Our results do not support the concept of MCA in hepatic gluconeogenesis and may indicate that the use of glycerol as a precursor for glucose synthesis by this pathway is of low physiological importance in Antarctic fish.

SUMMARY:Delta-based estimates of longtail hake biomass off Argentina were derived from the results of summer trawl surveys carried out on an irregular basis since 1987. Annual estimates of biomass within the whole area ranged from 1.2 to 4.5 million tons, consistent with those obtained by sequential population analysis. There was no clear trend throughout the period 1987-1995, but the 1987 estimate was higher than those for the same area during the years 1992-1995, and estimates since 1997 were much higher than the mean for the four-year period 1992-1995. Since 1992 the largest concentrations of fish have been between 50 and 100 m deep. Most of those were adults, small fish being scarce. Analysis of numbers-at-age showed the dominance of 4-8 year old fish in 1987 and from 1992 to 1994 and the existence of two very strong year-classes, those of 1993 and 1995.