Opportunistic migration and habitat use of the giant mottled eel Anguilla marmorata (Teleostei: Elopomorpha)

Takaomi Arai,Naoko Chino

doi:10.1038/s41598-018-24011-z

Takaomi Arai, Naoko Chino

Open Access

https://doi.org/10.1038/s41598-018-24011-z

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Abstract

Freshwater eels have fascinated biologists for centuries due to the spectacular long-distance migrations between their freshwater habitats and their spawning areas far out in the ocean. Although freshwater eels originated in the Indonesian region, remarkably little is known about the life history of tropical freshwater eels. The diverse migratory patterns and habitat choice between marine and freshwater environments by the giant mottled eel Anguilla marmorata Quoy & Gaimard, 1824 were examined by analysing the otolith strontium (Sr) and calcium (Ca) concentrations collected in Asian waters. The wide range of otolith Sr:Ca ratios indicated that the habitat use of A. marmorata was opportunistic among fresh, brackish, and marine waters. The present study first confirmed the occurrence of marine-resident eels that have never migrated into a freshwater habitat in A. marmorata. A. marmorata may have the same behavioural plasticity as temperate and other tropical anguillid species regarding whether to enter freshwater or to remain in estuarine and marine environments. Freshwater eels migrate flexibly among freshwater, brackish water, and seawater environments and it is now evident that their movement into freshwater is not an obligate migratory pathway but should be defined as an opportunistic catadromy, with marine and estuarine residents as ecophenotypes.

Highlights

Freshwater eels have fascinated biologists for centuries due to the spectacular long-distance migrations between their freshwater habitats and their spawning areas far out in the ocean
Because of the wide geographic range of A. marmorata, which is separated by several major landmasses, it is clearly unlikely to comprise a single panmictic population such as temperate anguillid species found in one particular region of a single ocean basin[7,8,9,10,11]
The occurrence of marine resident eels that have never migrated into freshwater habitat was first confirmed in the giant mottled eel Anguilla marmorata (Figs 2 and 3), marine residence has been found in other species and localities in coastal waters for both temperate and tropical eels[23,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]

Summary

Introduction

Freshwater eels have fascinated biologists for centuries due to the spectacular long-distance migrations between their freshwater habitats and their spawning areas far out in the ocean. The giant mottled eel Anguilla marmorata is a unique tropical freshwater eel that reaches large sizes of 2 m in length with a maximum weight of 21 kg[4] This species has the widest geographic distribution of the 19 species/ subspecies of freshwater eels[2] and is found longitudinally from the east coast of Africa to the Marquesas Islands in the southeast Pacific Ocean and as far north as southern Japan[2]. This species was found at the Palmyra Atoll in the central Pacific[5] and even farther to the east in the Galapagos Islands[6], which may indicate that it has an even wider geographic range than previously thought. Sampling location Poso, Indonesia Amami Islands, Japan Bonin Islands, Japan Quang Tri, Vietnam Quang Ngai, Vietnam Binh Dinh, Vietnam

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