Morphological and physiological changes of female tropical eels, Anguilla celebesensis and Anguilla marmorata, in relation to downstream migration

Abstract

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.

Age and growth of migrating tropical eels, Anguilla celebesensis and Anguilla marmorata

“…Freshwater crabs, chicken meat or earthworms were used as fishing bait. The eels caught other than in the weirs were regarded as non‐migrating eels that settled to grow in freshwater habitats, which is consistent with the reproductive characteristics of these eels (Hagihara et al, ).…”

“…Recently, Hagihara et al . () described the morphological and physiological characteristics of migrating tropical eels, using dozens of Celebes longfin eels Anguilla celebesensis Kaup 1856 and A. marmorata caught by weirs set near the outlet area of Poso Lake (1° 46′ S; 120° 38′ E) on Sulawesi Island, Indonesia. The female A. celebesensis that seem to migrate only a short distance from the Poso River mouth into Tomini Bay (Aoyama et al, ; Wouthuyzen et al, ) showed remarkably advanced oogenesis (mean ± s.d .…”

“…The female A. celebesensis that seem to migrate only a short distance from the Poso River mouth into Tomini Bay (Aoyama et al, ; Wouthuyzen et al, ) showed remarkably advanced oogenesis (mean ± s.d . gonado‐somatic index, I G = 6·9 ± 1·8) in comparison with the migrating A. marmorata ( I G = 3·1 ± 0·8) (Hagihara et al, ) that appear to reproduce in the spawning area of the North Pacific Ocean population of that species in the North Equatorial Current region, where the A. japonica also spawns (Miller et al, ; Kuroki et al, ; Tsukamoto et al, ). That study on the Poso Lake–River system eels did not include information about the ages of the eels, so the age and growth of silver‐phase and migrating anguillid eels in tropical areas has remained poorly understood.…”

Seasonal Changes in Species Composition of Glass Eels of the Genus Anguilla (Teleostei: Anguillidae) Recruiting to the Cagayan River, Luzon Island, the Philippines

“…Considering the sympatric distribution of several anguillid species in the tropics and their specific reproductive characters that vary interannually (see Aoyama 2009, Miller 2009, Hagihara et al 2012, it can be reasonably supposed that the species composition of glass eels in the tropics changes drastically year by year. This has also been reported for A. celebesensis in the Poigar River, Sulawesi Island, Indonesia (Sugeha et al 2001).…”

Evaluation of the population structure of Anguilla bicolor and A. bengalensis using total number of vertebrae and consideration of the subspecies concept for the genus Anguilla

“…The genus Anguilla is currently recognised as comprising 16 species (Ege 1939;Castle & Williamson 1974;Watanabe 2003;Watanabe et al 2009a;Watanabe & Miller 2012), three of which are further divided into two subspecies (Ege 1939). The basic biology of temperate eels is generally known, but information about tropical eels that comprise two-thirds of all anguillid eel species is much more limited Watanabe & Miller 2012), with only a few studies having been conducted (Hagihara et al 2012). The tropical and temperate eels consist of 11 and 5 species, respectively.…”