Age and growth of larval and juvenile walleye pollock, Theragra chalcogramma (Pallas), as determined by otolith daily growth increments

Abstract

The validity of otolith increments for determination of age in days in larval and juvenile walleye pollock, Theragra chalcogramma (Pallas), was examined in ground and etched otoliths (sagittae) by scanning electron microscopy. Rearing of larvae from incubated fertilized eggs and a time-marking experiment with reared juveniles showed that the first increment occurred at hatching and increments were then formed on a daily basis. The age of wild fish (11–96 mm in total length) collected from April through August, 1980 and May, 1981 in Uchiura Bay, Hokkaido, was determined by counting increments. The hatching period was estimated to be from early January to late March. Logistic curves were fitted to the body growth and the otolith growth. Both curves showed a maximum growth at ≈ 125 days after hatching when the fish were 61 mm in total length. There was a linear relationship between total length and otolith length in logarithmic scales. The observed interrelationships between total length, otolith length and fish age (number of increments) validated the otolith reading for analyses of the initial growth of walleye pollock. A possibility that otolith microstructure changes can be utilized as information source of some ecological events in the early life history is suggested.