Hatching season and growth of Pleuragramma antarcticum larvae near the Antarctic peninsula in austral summer 1993/94

Hatching season and larval growth of Pleuragramma antacticum in the water off Antarctic Peninsula were determined by the examination of growth increments in otoliths. The samples were collected by Bongo plankton net or MOCNESS from December 1993 through January 1994. P. antacticum was predominated (54 inds. out of 77 fish larvae) in ichthyoplankton samples, and occurred mainly in cold water of the Weddell Sea. Body length of P. antacticum ranged from 12.0 to 67.3 mm. Otolith radii (R) ranged from 150 to 260 μm, and linearly related to body size (L); R = - 43.6 + 5.99 L (r2=0.79). The mean size of otolith cores was about 50 μm in diameter. The width of the growth increments was narrow near the core, but it became broader at around 50 - 100th increments (ca. 1.3 μm). However, it decreased thereafter toward the edge maintaining the size of ca. 0.5 μm. Assuming that a growth increment was deposited daily after hatching, P. antacticum seems to be hatched during June - July, because the mean number of increments was 178.3 (standard deviation = 12.8). With the samples we examined, we speculate that there exist two hatching periods for P. antacticum: The large larvae (40-50 mm) hatched in winter (June - July), while the small ones in early summer (December) .