Sexual reproduction in a fissiparous holothurian species, Holothuria leucospilota Clark 1920 (Echinodermata: Holothuroidea)

Abstract

\n \t\t\tHolothuria leucospilota Clark 1920 inhabiting tropical Darwin waters primarily undergo asexual reproduction by fission throughout the year (Purwati 2001). However, there is also evidence of sexual reproduction. Monthly sampling from August 1998 to January 2000 revealed that the gonadal tubules within each individual of H. leucospilota grew simultaneously. Complete spawning, where the oocytes throughout the gonad have equal opportunity to be released in one spawning event, could therefore be expected. Postspawning tubules were absorbed, resulting in the disappearance of gonads between reproductive cycles. The development of gonadal tubules in this holothurian does not conform to the “tubules recruitment model” proposed by Smiley (1988), as reassessed by Sewell et al. (1997). Aseasonal reproductive cycle with a restricted spawning period was recognised in the population studied. The resting stage that occurred simultaneously amongst individuals in the population made it possible to estimate gametogenesis, which may take less than a year. It is likely that gamete release occured in the period between new moon and full moon of April, at the end of the wet season in Darwin. The continuous flooding of the reefs during this period is thought to be effective for fertilisation.\n