The Purpose of the present paper is to report the study on the age and growth of a Sterno optychid Fish Maurolicus muelleri in the south western waters of the Sea of Japan. A total of 1823 samples were collected by midwater trawl, and the otolith of 258 specimens out of them were used for the age determination. The results through this investigation are summarized as follows.
1. The relationship between standard length (L mm) and the radius of otolith (R mm) can be described by the following equation.
All the radii of annual marks on otolith were standardized by this equation.
2. By monthly change of marginal growth of otolith, it was estimated that the annual mark (hyaline zone) was formed every year through the long period from December to April.
3. Fish was classified into two groups; spring brood and autumn brood, by the size of radius of annual mark on otolith. That is to say, one whose radius of the inner opaque zone was over 0.584mm was put into spring brood and one with the value less than this figure into autumn brood.
4. It may be estimated that the two groups, both spring brood and autumn brood, atain sexual maturity in about a year and the lifetime si around 20 months.
5. The relationship between the number of months (t) and the standard length (L mm) is estimated as follows.
Spring brood: Lt=56.1(1-e-0.119(t-0.315))
Autumn brood; Lt=56.3(1-e-0.08(t+3.005))
Female is larger than male in both groups.