Assessing Temporal Patterns and Species Composition of Glass Eel (Anguilla spp.) Cohorts in Sumatra and Java Using DNA Barcodes

Abstract

Anguillid eels are widely acknowledged for their ecological and socio-economic value in many countries. Yet, knowledge regarding their biodiversity, distribution and abundance remains superficial—particularly in tropical countries such as Indonesia, where demand for anguillid eels is steadily increasing along with the threat imposed by river infrastructure developments. We investigated the diversity of anguillid eels on the western Indonesian islands of Sumatra and Java using automated molecular classification and genetic species delimitation methods to explore temporal patterns of glass eel cohorts entering inland waters. A total of 278 glass eels were collected from monthly samplings along the west coast of Sumatra and the south coast of Java between March 2017 and February 2018. An automated, DNA-based glass eel identification was performed using a DNA barcode reference library consisting of 64 newly generated DNA barcodes and 117 DNA barcodes retrieved from BOLD for all nine Anguilla species known to occur in Indonesia. Species delimitation methods converged in delineating eight Molecular Operational Taxonomic Units (MOTUs), with A. nebolusa and A. bengalensis being undistinguishable by DNA barcodes. A total of four MOTUs were detected within the glass eel samples, corresponding to Anguilla bicolor, A. interioris, A. marmorata, and A. nebulosa/A. bengalensis. Monthly captures indicated that glass eel recruitment peaks in June, during the onset of the dry season, and that A. bicolor is the most prevalent species. Comparing indices of mitochondrial genetic diversity between yellow/silver eels, originating from several sites across the species range distribution, and glass eels, collected in West Sumatra and Java, indicated a marked difference. Glass eels displayed a much lower diversity than yellow/silver eels. Implications for the management of glass eel fisheries and species conservation are discussed.

Barcoding a glass eel migration: a snapshot of taxa migrating upstream in the Palu River, Central Sulawesi, Indonesia

“…One reason for this knowledge gap is that the early stages of many diadromous taxa recruiting to freshwater are hard to identify to species level, and sometimes even to higher taxonomic levels, based on morphological methods alone. This is the case for anguillid glass eels [15] and other fishes [18,19] as well as invertebrates such as crustaceans [20] and molluscs [21,22].…”

“…Early life-stages of catadromous and amphidromous fish tend to recruit to freshwater habitat in large schools; while some temperate species of anguillid eels can recruit in monospecific schools, tropical anguillid eels and other catadromous or amphidromous species typically migrate to freshwater in multi-species schools [6,9,[15][16][17]. As tropical eels recruit in multi-species schools, typically including more than one species of the genus Anguilla as well as other diadromous species, effective management of these and other diadromous resources requires reliable data on the species composition of the diadromous taxa recruiting in multi-species schools into riverine habitat.…”

“…As tropical eels recruit in multi-species schools, typically including more than one species of the genus Anguilla as well as other diadromous species, effective management of these and other diadromous resources requires reliable data on the species composition of the diadromous taxa recruiting in multi-species schools into riverine habitat. However, such data are limited in geographical and taxonomic scope, in particular with respect to tropical anguillid glass eels recruiting to rivers in Indonesia [15]. One reason for this knowledge gap is that the early stages of many diadromous taxa recruiting to freshwater are hard to identify to species level, and sometimes even to higher taxonomic levels, based on morphological methods alone.…”

“…The advances over recent decades in molecular biology include the development of DNA barcoding techniques, enabling identification of a specimen from the nucleotide sequence of a molecular marker; this is a specified region of the genome (barcode) which is highly conserved within a given taxon (ideally species) but differs between taxa [23,24]. This method is increasingly used for identifying specimens that are challenging or impossible to identify based on morphology, such as cryptic species and larval or juvenile stages [18][19][20][21][22]25], including anguillid glass eels [15]. The main limitation of DNA barcoding is that identification depends on the availability of a reference sequence for the taxon being identified in the public nucleotide sequence databases [24].…”

Molecular Identification of Elvers (<I>Anguilla</I> spp.) from River Estuaries in Central Java, Indonesia Using DNA Barcoding Based on <I>mt</I>DNA CO1 Sequences

“…If these characters' information is available, germplasm variation can be accessed effectively and efficiently for conservation and further research (Anggraeni et al, 2008). Molecular identification of eels has been successfully conducted (Arai et al, 2020;Alter et al, 2015;Wibowo et al, 2021). Furthermore, detection of the presence and diversity of eel revealed by environmental DNA analysis (Kasai et al, 2021;Takahashi et al, 2021).…”