A field guide for glass eel species identification

Abstract

Anguillid eels are unique catadromous fishes categorized as a group of species that undergo long-distance migrations, traveling between growth habitats in freshwater environments while breeding and spawning in far-deep oceanic areas. Currently, stocks of temperate eels are known to have dramatically decreased since natural and anthropogenic factors have created severe impacts on wild populations. To meet market needs, people have been looking for substitutes by using other eels that inhabit the tropics. Most of the production in the eel culture industry is realized through the rearing of wild-caught juveniles called “glass eels.” For this reason, since the mid-1990s, capture fisheries with particular interest in glass eels have increased rapidly. Previous studies identifying the Anguillid eel species in Southeast Asia were focused on looking at specific pigmentation patterns and morphological characteristics. Nevertheless, it was still hard to identify the glass eels with the naked eye. In the field, the fishers and consolidators will separate the glass eels into only two species: Anguilla bicolor and Anguilla marmorata. However, this is not very clear since some species, such as A. bengalensis and A. luzonensis, look like A. marmorata. Therefore, this field guide will describe visual observations of anguillid eels from the wild to enable the identification of glass eel species based on differences in morphological characteristics.