Zoological Studies

Reproductive Mode of the Blue-striped Angelfish Chaetodontoplus septentrionalis in Northeastern Taiwan

Kuan-Yu Chen and Wann-Nian Tzeng (2009) The blue-striped angelfish Chaetodontoplus septentrionalis Temminck and Schlegel 1844 is a coral reef fish distributed from Hong Kong through Taiwan to southern Japan.  This species has potential in the future aquaculture industry of marine ornamental fishes.  However, fundamental knowledge of the reproductive biology of this species is scant.  To understand its reproductive mode, the gonadosomatic index (GSI) and gonadal histology of the fish were examined based on 155 individuals collected monthly from the reef zone of Ilan County, northeastern Taiwan between Jan. 2003 and Jan. 2004.  The GSI of females significantly increased from late spring to mid summer (May-July), and that of males increased earlier and declined later (Mar.-Aug.) than females.  Seasonal changes in the ovarian maturity stage composition indicated that the peak spawning season of C. septentrionalis occurs in summer.  The reproductive activity of C. septentrionalis drastically decreased when water temperatures exceeded 28°C.  The histological analysis of the ovaries indicated that this fish is a partial spawner with synchronous occurrence of previtellogenic and vitellogenic oocytes and secondary oocytes during the spawning season.  The total length of the fish ranges 143.1-215.4 mm.  The mean length of males (180.7 ± 13.9 mm) is larger than that of females (172.8 ± 12.0 mm), and the proportion of males increased in large size classes indicating sexual size dimorphism in C. septentrionalis.  The presence of a male with a few oogonia in its testes suggests that C. septentrionalis exhibits hermaphroditism.