A study by Japanese scientists to be published in an upcoming issue of the journal Ichthyological Research has demonstrated that the swamp eel Monopterus albus, previously thought to be a single, wide-ranging species, may actually consist of several more geographically circumscribed ones.
Seiji Matsumoto and coauthors base their conclusions on molecular phylogenetic analyses of a 514-base pair mitochondrial 16S rRNA sequence conducted for 84 specimens from 13 localities in Southeast and East Asia.
The authors found that the specimens of M. albus analysed could be genetically delineated into three clades based on geographical populations , with each clade exhibiting its own reproductive behaviour.
In the China-Japan clade, the breeding male digs a nest hole and then makes a foam mass.
The eggs are spawned into this foam mass, where they are fertilized. After hatching, the male keeps the larvae in his buccal cavity until they begin to breathe air.
In the Ryukyu Islands clade, the breeding males behave similarly, but do not brood the larvae in his buccal cavity.
Finally, members of the Southeast Asian clade do not build foam nests, but lay their eggs under floating plants and do not exhibit parental care.
For more information, see the paper: Matsumoto, S, T Kon, M Yamaguchi, H Takeshima, Y Yamazaki, T Mukai, K Kuriiwa, M Kohda and M Nishida (2009) Cryptic diversification of the swamp eel Monopterus albus in East and Southeast Asia, with special reference to the Ryukyuan populations. Ichthyological Research doi: 10.1007/s10228-009-0125-y