Abstract
Abstract: Growth and age structure of the lancelet Branchiostoma belcheri was studied in the Seto Inland Sea, Japan, throughouthe year. A total of 3, 601 lancelets were collected by means of dredging. Spawning of the lancelets occurred from late June to late July. Changes in modal size on the length-frequency histograms showed that the lancelets settled on sandy sediment after four to five months of planktonic life when they grew to 7.0 mm BL. Mean body lengths of the lancelets at an age of one, two and three years appeared to be 10.9, 28.0and 33.0 mm, respectively. Most individuals developed gonads after an age of two years at 25 mm BL. The sex ratio(males: females)was 0.97: 1, and the size composition was not diffbrent between sexes. Growth rate and life span of lancelet species increased and decreased at the high temperature habitats, respectively.
