Species composition of glass eels (Anguilla spp.) recruiting to the Palu River, Central Sulawesi

Abstract

Demand for tropical eel seed has been increased and many tropical eel populations are under pressure. To conserve eel biodiversity and manage eel populations sustainably, it is necessary to identify eel species and their recruitment patterns at regional and watershed scales. The research objective was to determine the species composition and temporal recruit-ment patterns of glass eels recruiting to Palu River in Central Sulawesi. Glass eels sampling were conducted in January-April 2009, May-November 2010 and April-December 2011. Identification under anaesthetic (15-17.5 ppm clove oil solution) was based mainly on the number of ano-dorsal vertebrae (ADV). Species composition was dominated by two commercially species, Anguilla marmorata and A. bicolor pacifica with substantial variation and no clear temporal patterns. Specimens of other species that important from conservation and biodiversity aspects were present at each month but cannot be accurately identified using the ADV method. DNA analysis method is required to identify these specimens.

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

“…However, doubt remained regarding the identity of glass eels with diagnostic traits with overlapping ADV ranges (all in the range 6-12) and a lack of other distinguishing features at that life stage. These were: A. borneensis, A. celebesensis and A. luzonensis [17]. While lack of proof of presence is not proof of absence, and one or both of the other species may (regularly or occasionally) recruit to the Palu River, our results confirm that A. celebesensis does recruit to the Palu River.…”

“…This similarity between a river flowing into the Makassar Strait on the west coast of Sulawesi and a river flowing into Tomini Bay on the east coast of Sulawesi indicates that the main diadromous taxa associated with glass eel migrations are likely to be similar in other rivers around Sulawesi, in particular with respect to fish and crustaceans. Previous studies on the glass eels recruiting to the Palu River have identified A. marmorata and A. bicolor pacifica [17], findings confirmed by the heavy exploitation of adult eels in the watershed [44]. However, doubt remained regarding the identity of glass eels with diagnostic traits with overlapping ADV ranges (all in the range 6-12) and a lack of other distinguishing features at that life stage.…”

“…All specimens were photographed, measured and weighed. The anguillid glass eels were also placed under a microscope (x 40 magnification) to observe and photograph the tail spot melanophore pattern [17] and count the anodorsal vertebrae [26]. Due to the small size of most specimens, the whole organism was used as a sample for DNA barcoding, with the exception of one fish (code IKP-1) from which fin clippings were taken.…”

“…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.…”

“…The Palu River in Central Sulawesi, Indonesia is one of many rivers in Indonesia where anguillid glass eel are known to recruit in large, multispecies schools [17]. Studies using two morphological methods concluded that between three and five anguillid eels recruit to the Palu River in Central Sulawesi, Indonesia with interannual and seasonal variations in species composition, and size structure.…”