Skin coloration and habitat preference of the freshwater Anguilla eels

Abstract

The genus Anguilla comprises 16 species and three subspecies of freshwater eels, which can be further divided into marbled and plain eels in terms of skin coloration on their backs. Owing to the overlap of geographical distributions between most marbled and plain eels in tropical/subtropical regions, the coexistence of marbled and plain eels in the same river is common. To understand the correlation between eel skin color and its habitat preference in the river, the distribution patterns of all anguillid eels were collected and analyzed. Results showed that all marbled eels distribute in tropical/subtropical areas and preferred the middle/upper reaches. The plain eels distributed both in temporal and tropical/subtropical areas, and preferred to inhabit the middle/lower reaches and estuaries. Plain skin coloration may help them easily remain hidden in a sandy and muddy environment, which is common in estuaries and lower reaches of rivers in tropical/subtropical areas, while mottled skin coloration more easily blends in with substrates such as cobble, gravel, and fallen leaves which are commonly found in the upper reaches of rivers in the tropical/subtropical areas. The different habitat preference between marbled and plain eels in the tropical/subtropical areas are likely a result of adaptive evolution to avoid potential interspecifi c competition, and this fi nding is meaningful for developing applicable management plans for eels.