Biology of the Amphioxus, Branchiostoma belcheri in the Ariake Sea, Japan I. Population Structure and Growth

概要

論文の詳細を見る
We investigated the population structure and growth of the amphioxus Branchiostoma belcheri for four years in the southern Ariake Sea, Japan. We counted 62-66 myotomes and 251-310 dorsal fin-ray chambers, and these results support that this species is an intermediate form of B. belcheri and its subspecies B. belcheri tsingtauense. The ratio of females to males was 1:1.12. Males were more numerous than females among small individuals (<40mm body length), but we found no significant differences among large animals (≥50mm body length). Spawning occurred from mid June to early July. Groups of newly settled young appeared from January to June of their second year. We observed a large fluctuation between years in the numbers of newly settled young. The estimated size of one-year-old individuals was 19.4mm in body length; within the next 12 months, they reached 32.1mm. Three- and four-year-old individuals measured 38.6mm and 45.8mm, respectively. Few grew beyond 60mm; the largest specimen collected was a 64mm male.
2003-07-25