Otolith microstructure of juvenile mackerel icefish (Champsocephalus gunnari) (Channichthyidae) in the South Georgia area
The otolith microstructure of juvenile mackerel icefish (Champsocephalus gunnari) (5.5–13.3 cm in length) was analysed using samples taken during a trawl survey of juveniles in February–March 2002 on the South Georgia shelf. Juvenile fish comprised two year classes arising from spawning in the 1999/2000 and 2000/01 split-years. The mean width of daily otolith growth increments decreased from 6 μm during the first 100 days (total length (TL) 4.5 cm) to 2.8 μm at 500 days (TL 13.1 cm). The pelagic stage of egg incubation development for fish of the 2001/02 year class lasted four months. This was estimated based on a retrospective count of daily increments. TL varied from 5.5 to 10.4 cm for fish in their first year (120–250 days) to 12.5–13.3 cm in 1-year-old fish (477–533 days). The radius of the first annulus ranged from 0.7 to 1.3 mm. The relationship found between fish length and daily otolith increments could be used for age differentiation of juvenile fish between consecutive year classes.