No significant differences were found in mean ages among months within any one species, whereas significant differences were found among species. Hatching was estimated to occur throughout almost the entire year in A. celebesensis and A. marmorata compared with intermittently over about 6 mo in A. bicolor pacifica. Based on year-round recruitment of A. bicolor pacifica at the mouth of the Poigar River in an earlier study and age at recruitment being constant throughout the year, the spawning season of this species may also occur throughout the year. In all species examined, positive linear relationships were found between age at metamorphosis and age at recruitment, suggesting that early metamorphosing larvae were recruited to freshwater habitats at an early age. Year-round recruitment of tropical glass eels to the river mouth would necessarily follow year-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.

In order to determine the early life history and recruitment mechanisms of tropical eels AnguiUa spp. in the Indo-Pacific, the timing of metamorphosis and age at recruitment to freshwater habitats were established from otolith microstructure and microchemistry analyses of juveniles of Anguilla celebesensis, A. rnarrnorata and A. bicolor bicolor. Otolith increment width markedly bicolor bicolor. In all species exam~ned, close linear relationships were found between ages at metamorphosis and recruitment, suggesting that individuals which metamorphosed earlier were recruited to freshwater habitats at a younger age.

To understand ecological and behavioral aspects of inshore migration of tropical eels, Anguilla spp., we collected 32 836 glass eels in the Poigar River estuary on north Sulawesi Island, Indonesia, in monthly collections from 1997 to 1999. The specimens were identified using morphological characters, and 3 species, A. celebesensis, A. marmorata, and A. bicolor pacifica, were found each year in fluctuating abundances. A. celebesensis was the most abundant species and comprised 73.5, 79.5, and 81.9% of all glass eels recruiting to the estuary of the Poigar River in 1997, 1998, and 1999, respectively. This species was relatively abundant in all 3 years with peaks during June in 1997 and 1998, and during September in 1999. A. marmorata was the second most abundant species and comprised 23.8, 18.8, and 17.7% of the yearly catches, respectively, and reached peaks in abundance during June in 1997 and 1998, and during January in 1999. A. bicolor pacifica comprised only 2.7, 1.7, and 0.3% of the yearly catches, respectively, with peak catches in June in 1997, in January in 1998, and in January and February in 1999. A. celebesensis and A. marmorata were collected almost throughout the year in 1997, 1998, and 1999, suggesting that in contrast to the temperate eels that recruit during half the year from winter to spring, these tropical eel species recruit to some degree throughout the year. Glass eels clearly were more abundant during new moon sampling events, with a total of 3075, 183, 3, and 90 glass eels collected in 10 sampling periods during new moon, waxing moon, full moon, and waning moon, respectively. All glass eels were collected at night (18:00 to 05:00 h) when light intensity ranged from 0 to 1.86 lux, and no glass eels were collected during the day (06:00 to 17:00 h) when light intensity ranged from 500 to 150 000 lux. During new moon, more glass eels were collected during flood tide than during ebb tide. These results suggest that a greater number of glass eels recruited to the Poigar River estuary at night, during new moon and during flood tide.

No abstract

In order to determine the species composition and inshore migration of the tropical eels Anguilla spp. migrating to an Indonesian river, we collected 21 633 glass eels at the mouth of the Poigar River, north Sulawesi Island, throughout 1997, and subjected these samples to both morphological examination and polymerase chain reactionrestriction fragment length polyrnorphism (PCR-RFLP) analysis. Three species, Anguilla celebesensis, A. marmorata and A. bicolorpacifica, were found throughout the season in fluctuating abundance, while the previously recorded A. borneensis was not recognized in the study. A. celebesensis constituted a dominant 88.3 % of all glass eels migrating to the Poigar River in 1997, and was seen throughout most of the year, with a peak in May and June. A. marmorata (11.3%) was also seen throughout most of the year, with peak occurrence in June. A. bicolorpacifica (0.4 %) occurred only in January, March, April, October and December. Inshore migrationConsiderable knowledge has been accumulated on the inshore migration and early life history of juveniles of numerous temperate anguillid species, such as

The morphological and physiological characteristics of migrating and non-migrating female tropical eels, Anguilla celebesensis and Anguilla marmorata were examined in relation to their downstream migration on central Sulawesi Island, Indonesia. Migrating eels (64 A. celebesensis and 37 A. marmorata) were obtained from weirs set near the outlet area of Poso Lake and non-migrating eels (21 A. celebesensis and 21 A. marmorata) were sampled by set-lines and eel pots in Poso Lake, its inlet rivers, and in the La River system during February 2009 to October 2010. In both species, values of eye index, pectoral-fin length index, gonado-somatic index (I(G)), hepato-somatic index, swimbladder-somatic index and cardio-somatic index of migrating eels were significantly higher than those of non-migrating eels and the gut-somatic index values of the migrating eels were significantly lower than that of non-migrating eels. When silvering stages of eels were classified by the silvering index for Anguilla japonica, in A. celebesensis, all non-migrating eels were Y1 stage and the migrating eels consisted of Y2, S1 and S2 stages eels. In A. marmorata, the non-migrating eels consisted of Y1 and Y2 eels, and the migrating eels consisted of Y2 and S1 eels, but there were no S2 eels. Results of principal component analysis (PCA) of morphological and physiological variables suggested that these characteristics changed drastically between the Y1 and Y2 stages in A. celebesensis, while A. marmorata showed a gradual change with silvering, which differs from the temperate species A. japonica. The mean ±S.D. I(G) value of migrating A. celebesensis (6.9 ± 1.8, 3.3-11.4) was very high and that of A. marmorata (3.1 ± 0.8, 1.8-5.7) was comparatively low. The very different rates of maturation that were found between these two species provide support for the hypothesis that the reproductive characteristics of silver eels can reflect their migration scale.

No abstract

To validate daily increments in otoliths of the tropical freshwater eel Anguilla celebesensis, a time-reference mark was incorporated in the otoliths of glass eels by immersing the eels in alizarin complexone (ALC) solution. They were subsequently reared in aquaria for 10 or 20 days, and the increments outside a fluorescent red ALC mark were counted. The numbers from the 10- and 20-d experiments were 9.4 ± 0.9 (mean ± SD) and 19.4 ± 1.4, respectively, suggesting daily deposition of otolith increments. Precise examination of otolith microstructure from the core to the edge showed gradual changes in increment width with no discontinuous structural features, suggesting that increments were deposited continuously from hatching to time of sacrifice. It was thus concluded that otolith increments in this species can be used for daily age determination.