Abstract
Anguillid eels of the genus Anguilla, which have a unique catadromous life history, are widely distributed across many parts of the world. However, little research has been conducted on the behavioural mechanisms of habitat segregation between sympatric species in tropical anguillid eels. To understand the ecological and behavioural mechanisms involved in the life history and migration of tropical anguillid eels, strontium (Sr):calcium (Ca) ratios were examined in otoliths of A. bengalensis bengalensis (41 specimens) and A. bicolor bicolor (130 specimens) collected from ten rivers in northwestern Peninsular Malaysia. The otolith Sr:Ca ratios revealed different habitat use between the two species. The broad range of otolith Sr:Ca ratios and habitat shift found in A. bicolor bicolor suggested that its habitat utilization was opportunistic in environments of varying salinity. A. bicolor bicolor prefers to live in the midstream to downstream areas with tidal influences. A. bengalensis bengalensis, however, was found to only reside in freshwater environments throughout their continental growth. A. bengalensis bengalensis tends to live in upstream area with no tidal influence. Their habitat use, migratory history, and habitat distribution indicate that habitat segregation occurs between the two species, leading to the different habitat preferences in tropical river systems.
Highlights
The anguillid eels, genus Anguilla Schrank, are widely distributed across the globe
The tropical eels, Anguilla bengalensis bengalensis, A. bicolor bicolor and A. marmorata have been reported in northwest Peninsular Malaysia[7,13,14,15,16,17,18]
Research on the migration and life history of tropical anguillid eels has revealed the origin of catadromy in anguillid eels and how the thousands of kilometres of large-scale migration in temperate eels have been established in contrast to the few hundred kilometres of local migration in tropical eels[19]
Summary
The anguillid eels, genus Anguilla Schrank, are widely distributed across the globe. There are nineteen species and subspecies of the freshwater eels, thirteen of which live in tropical areas[1,2]. The year-round spawning and stable larval development stimulate year-round recruitment to continental habitats in tropical eels[8,9,10,11,12], leading to significantly different life history characteristics between temperate and tropical anguillid species. Sr:Ca ratios from core to edge reflect the salinity of the eel’s habitat throughout its lifetime[3] These studies found that some anguillid eels migrated to a freshwater environment in the growth phase while others did not, the reasons for the discrepancy why some eels at growth phase did not migrate to freshwater still remain unclear. We examined the migratory history and habitat use of the tropical freshwater eels, Anguilla bengalensis bengalensis and A. bicolor bicolor in West Malaysia. The objectives of this study were to (1) reconstruct the migratory history of tropical anguillid eels by examining otolith Sr:Ca ratios along the life history transect, (2) estimate the Sr:Ca ratios in otolith edge parts to determine recent habitat use and (3) examine the habitat preference, species-specific migratory behaviours and habitat segregation between these two species
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