Recruitment mechanisms of tropical eels Anguilla spp. and implications forthe evolution of oceanic migration in the genus Anguilla

Otolith microstructure and microchemistry of the tropical eels Anguilla cel ebesensis Kaup, A. marmorata Quoy & Gaimard and A. bicolor pacifica Schmidt were examined in glass eels collected at the mouth of the Poigar River, no rth Sulawesi Island, Indonesia, throughout 1997. Ages at metamorphosis and recruitment, respectively, were 84 to 95 d and 104 to 118 d in A. celebesen sis, 114 to 158 d and 144 to 182 d in A. marmorata, and 129 to 171 d and 15 8 to 201 d in A. bicolor pacifica. No significant differences were found in mean ages among months within any one species, whereas significant differe nces were found among species. Hatching was estimated to occur throughout a lmost the entire year in A. celebesensis and A. marmorata compared with int ermittently over about 6 mo in A. bicolor pacifica. Based on year-round rec ruitment of A. bicolor pacifica at the mouth of the Poigar River in an earl ier study and age at recruitment being constant throughout the year, the sp awning season of this species may also occur throughout the year. In all sp ecies examined, positive linear relationships were found between age at met amorphosis and age at recruitment, suggesting that early metamorphosing lar vae were recruited to freshwater habitats at an early age. Year-round recru itment of tropical glass eels to the river mouth would necessarily follow y ear-round spawning and stable recruitment age. Such a recruitment mechanism differs from that of temperate eels, the latter having a limited spawning season followed by a limited period of recruitment.