Paradox fish is spiny eel relative

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The enigmatic Paradox fish, Indostomus paradoxus, is a close relative of the spiny-eels according to the most recent DNA study of fish relationships.

New research by Japanese and French scientists, published in the most recent volume of the journal Molecular Phylogenetics and Evolution, suggests that the paradox fish is more closely related to synbranchiform (swamp and spiny) eels than it is to other gasterosteiform fishes (sticklebacks, pipefishes and their relatives).

The relationships of the bizarre Paradox fish, which lays green eggs and looks like a cross between a pipefish and a stickleback, have been of interest to scientists since they were first discovered in the 1920s.

Previous theoriesThough the precise relationships of this tiny fish have always been controversial, most scientists had concluded that they were most closely related to the gasterosteiform fishes.

Gasterosteiforms are a diverse group of fishes that typically have tube-shaped mouths and a body covered in plates of bony armor.

They are commonly divided in to two groups, the Syngnathoidei that includes the pipefishes, seahorses, seamoths and their relatives and the Gasterosteoidei that includes the stickleback and its relatives.

Since its description the paradox fish has switched between the two gasterosteiform groups on numerous occasions, with different scientists arguing for its placement in one or the other.

Research on the development of the paradox fish conducted in 2002 at the Smithsonian Institution in Washington DC, suggested that the tiny paradox fish was in fact more closely related to the sticklebacks that it was to the pipefishes amongst gasterosteiforms, based on similarities in the development of body armor and other characteristics.

Strange bedfellowsNot only does the most recent phylogenetic research by Japanese and French scientists suggest a novel placement for the paradox fish as a close relative of swamp and spiny-eels but it also suggests that the two groups of gasterosteiform fishes (the Syngnathoidei and Gasterosteoidei) may be more distantly related than currently believed.

The DNA evidence suggests that the pipefishes, seahorses, seamoths and their close relatives may be more closely related to gobies that they are to the sticklebacks, which the Japanese and French scientists suggest are close relatives of the eel-pouts and gunnels.

Though these grouping may seem somewhat bizarre, several previous DNA based studies have recovered similar results, suggesting that gasterosteiform fishes may not be as closely related as currently believed.

For more details on the relationships of the gasterosteiform fishes see the paper: Kawahara, R. M. Miya, K. Mabuchi, S. Lavoue, J. G. Inoue, T. P. Satoh, A. Kawaguchi, M. Nishida. (2008). Interrelationships of the 11 gasterosteiform families (sticklebacks, pipefishes, and their relatives): A new perspective based on whole mitogenome sequences from 75 higher teleosts. Molecular Phylogenetics and Evolution, 46: 224-236.