Can displaced Anguilla marmorata return to their original habitat? Daily tracking study of their homing behavior

Anguilla marmorata collected in the Odana River lower reaches were passive integrated transponder-tagged displaced and released into the upper river reaches (54 up-transported eels), and eels collected in the upper reaches were tagged and released downstream (52 down-transported eels). Their movements were detected once per day for 10 days using a portable radio-frequency identification (RFID) system. The homing rate of the down-transported eels was 38.9%, compared to 3.7% for the up-transported eels, suggesting that eels inhabiting upstream areas have relatively high fidelity to their habitats and downstream eels have less fidelity.

Contrasting riverine distribution and habitat use of the Japanese eel, Anguilla japonica, and the giant mottled eel, Anguilla marmorata, in a sympatric river

Electrofishing and visual observations revealed contrasting riverine distribution and habitat use of the Japanese eel, Anguilla japonica, and the giant mottled eel, Anguilla marmorata, in a relatively gentle-slope river of Southern Kyushu, Japan. A. japonica was distributed in the lower and upper reaches. A. marmorata inhabited the middle reaches with relatively fast water velocity, heterogeneous water depth, coarse substrata and no adjacent paddy fields. This may have important conservation implications because a decrease in environmental diversity and/or river connectivity could result in the disappearance of A. marmorata habitats.

Genomic signatures for latitudinal selection in the tropical eel Anguilla marmorata

Selection acting across environmental gradients, such as latitudes, can cause spatial structuring of genomic variants even within panmictic populations. In this study, we focused on the within-generation latitudinal selection between northernmost and southernmost individuals of the North Pacific population of a tropical eel Anguilla marmorata, which shares its northernmost distribution with a temperate eel Anguilla japonica. Whole-genome sequencing data indicated that the northernmost and southernmost individuals of A. marmorata belong to a single panmictic population, as suggested by previous studies. On the contrary, parts of genomic regions across multiple chromosomes exhibited significant genetic differentiation between the northernmost and southernmost individuals, and in these genomic regions, the genotypes of the northernmost individuals were similar to those of A. japonica. These findings suggested within-generation latitudinal selection of A. marmorata, which might have led to genetic closeness between northernmost A. marmorata and A. japonica.