Scientists have undertaken a molecular study on one of the world's tiniest fish and have found that its genus contains more species than currently recognised.
The Schindleria genus of marine gobies includes some of the world's smallest and youngest reproducing vertebrates, among them what was once the world's smallest fish species, Schindleria brevipinguis, fully grown at just 8.4mm/0.3".
Current thinking places three species in the genus: Schindleria brevipinguis, S. pietschmanni and S. praematura.
However, a molecular analysis of the fishes has suggested that as many as 21 genetically distinguishable species may be present in the sample examined.
The study, which was undertaken by Kon, Yoshino, Mukai and Nishida of the University of Tokyo's Department of Marine Bioscience, is due to be published shortly in the journal Molecular Phylogenetics and Evolution.
It examined partial mitochondrial 16S rRNA sequences from specimens collected in the Ryuku and Ogasawara Islands around Japan, and showed that one of the species - Schindleria praematura - may contain as many as 15 cryptic species, which have previously gone unnoticed by taxonomists.
The authors said: "This discovery of many cryptic species in Schindleria suggests that the use of DNA sequences is necessary for species identification of such morphologically conserved taxa.
"Because molecular analyses should increase the number of hitherto unnamed and pseudonymous species, especially in tropical areas, it is proposed that DNA-based designation is necessary for such taxa in order to compile the full "species lists", although there is presently no consensus for the inclusion of DNA sequencing data in the formal descriptions of new species."
In morphological taxonomy, Schindleria are typically characterised by their larval-like form, which includes a slender, translucent, scaleless body - rather like that of a fry.
The three described species are told apart by only a combination of dorsal and anal fin ray counts.
Kon T, Yoshino T, Mukai T, Nishida M (2007) - DNA sequences identify numerous cryptic species of the vertebrate: A lesson from the gobioid fish Schindleria. Mol Phylogenet Evol. 2007 Jul;44(1):53-62. In Press.