Occurrence and biological characteristics of glass eels of the Japanese eel Anguilla japonica at the Cagayan River of Luzon Island, Philippines in 2009

Abstract

Background: The Japanese eel Anguilla japonica spawns in the North Equatorial Current in the Philippine Sea and their larvae are transported to their freshwater growth habitats in East Asia. Here we report the occurrence and biological characteristics of glass eels of A. japonica that were collected on northern Luzon Island of the Philippines, the southern limit of the distribution range of this species. Anguillid glass eels recruiting to the Cagayan River estuary in January and February 2009 were collected and identified using their morphological and genetic characteristics. Results: Among the 767 specimens, 52 glass eels collected in January were found to be A. japonica, while the remaining were tropical anguillid species. Age estimation revealed that the glass eels of A. japonica from northern Luzon Island were 147.2 ± 21.3 days old (mean ± sd) with a range between 111 and 185. The hatch dates of these A. japonica suggested that they were derived from at least four spawning events in the 2008 spawning season.

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

“…Tabeta et al (1976) found six A. japonica among 5,404 glass eels or elvers collected at the Cagayan River during 1970-1974, and Yoshinaga et al (2014 more recently identified 52 A. japonica glass eels from a total of 767 specimens sampled in 2009 from the same area. Following those reports, the study reported here also found A. japonica in this area, but only one glass eel in February 2009 among the 32,178 glass eels collected during a total of 29 months in the different years.…”

“…The specimens collected in the study re ported here were first classified morphologically into two groups, the short-finned eel (A. bicolor pacifica) or the long-finned eels (the other four species), based on the length between verticals through the anus and origin of the dorsal fin in percentage of the total length (AD/ TL), following previous studies (Ege 1939, Tabeta et al 1976, Watanabe 2003, Watanabe et al 2004, Leander et al 2012). Among the longfinned specimens (AD/ TL > 5), A. japonica was identified by the absence of cutaneous caudal pigmentation that is well developed in the other long-finned species (Tabeta et al 1976, Leander et al 2012, Yoshinaga et al 2014). …”

“…In Period II, 85 -96 long-finned specimens (A. celebesensis or A. luzonensis or A. marmorata) were randomly selected from each month, resulting in 1,209 specimens being identified using a partial sequence of the mitochondrial 16S rRNA gene. The genetic methods were described in detail elsewhere ( Han et al [2012] for Period I, Yoshinaga et al [2014] for Period II ).…”

“…However, the recent finding of a cryptic species, A. luzonensis, from Luzon Island ) indicates that the commercial exploitations of glass eels in this area has been carried out without clear biological or ecological information about the species being harvested. Indeed, Yoshinaga et al (2014) recently found that glass eels of A. luzonensis were collected by local fishermen at the estuary of the Cagayan River for export to East Asia in 2009. These facts strongly suggest the need for reassessment of the anguillid eels in this area to understand their life histories and ecology to facilitate their management and conservation.…”

Skin mucus C-type lectin genes from all 19 Anguilla species/subspecies

“…The methods used to extract genomic DNA from the 19 Anguilla species/subspecies samples are described elsewhere [18][19][20][21]. Generally, genomic DNA was extracted using a silica-based column, and it was subsequently preserved in Tris-EDTA buffer.…”