TEMPORAL CLARIFICATION OF THE TRANSITION FROM BLUE PHASE FINGERLING TO EARLY JUVENILE BROWN PHASE IN NOTOTHENIA ROSSII FROM THE SOUTH SHETLAND ISLANDS

Scales and whole otoliths were read for age determination of early stages of Notothenia rossii caught in Potter Cove, South Shetland Islands, in summer of years 2003-2006 and 2008. The sample was composed by blue phase fingerlings of 7-7.6 cm (TL) and age group 0 year and demersal young brown phase juveniles of 8.5-20.9 cm and predominant age groups 1-2 years. Counting of sclerites facilitated the interpretation of the rings, particularly in the central area of the scale. To clarify two issues of controversy in the literature: 1) we believe that the duration of the pelagic fingerling stage at sea is less than one year before migration to the demersal nearshore habitat; 2) the first well defined ring in scales corresponds to the first annulus, while a contiguous nearby ring is a secondary ring deposited after the first winter during the second year, attributable to a shift of habitat from pelagic to demersal. Our inferences, based on interpretation of the distinct sclerite structures that constitute the rings, are illustrated/supported by photographs. A von Bertalanffy growth curve was computed by combining age/length data of the juvenile phase of N. rossii from this and a previous study at Potter Cove, with literature data from the offshore adult population, resulting in the equation: