Lunar spawning in Siganus canaliculatus

A major spawning of the seagrass rabbitfish Siganus canaliculatus occurred 4 days after the new moon in both May and June 1993, and 7 days after the n ew moon in 1994. The gonadosomatic index (I-G) and serum vitellogenin (VTG) levels fluctuated according to the lunar cycle; I-G and VTG levels showed peaks at around the new moon and the waning moon, respectively, suggesting that spawning of this species is synchronized with the lunar cycle. Vitello genic oocytes appeared on day 2 after the first spawning and were fully mat ure on day 30. When a greater percentage of the most advanced oocytes attai ned the tertiary yolk stage, they formed a batch and separated from the adj acent group of smaller pre-vitellogenic oocytes, indicating that S. canalic ulatus is a multiple spawner with an ovary belonging to the group-synchrono us type of oocyte development. Batch fecundity, assessed using batches of o ocytes at and after the tertiary yolk stage, ranged from c 0.52 to 2.56 mil lion eggs. The relationship between batch fecundity (F) and fork length (L) can be represented as F=0.0536854L(5.07292) (C) 1999 The Fisheries Society of the British Isles.