Otolith microstructure and pelagic larval duration in two stocks of the Argentine hake, Merluccius hubbsi

Otolith microstructure of late larvae and early juveniles of both northern and southern stocks of Argentine hake (Merluccius hubbsi) was described, and the duration of the pelagic stage of the larvae was estimated. An irregular primordium of the otolith, enclosing growth increments originated from a central nucleus, is delimited by the formation of a variable number of accessory growth centres (AGCs). AGC formation in Argentine hake demands approximately one month, while fish total length increases from ca. 15 to 29 mm. The duration of the pelagic phase of the larvae was around two months for both stocks. By comparing the observed pattern of otoliths increments with previous osteological and behavioural studies it is suggested that hake settlement is, as in other species, a gradual process. Fish would grow faster as they acquire demersal habits being evidenced by the observed width increments. High linear correlations between otolith radius and fish total length were found in both stocks. Differential growth between Argentine hake stocks was found through comparisons of the radius of nucleus and primordium as well as the relationships between otolith radius and fish length.