New candidates for smallest vertebrate

Two recent scientific papers have described fish species that could—depending on the definition—be the world’s smallest vertebrate.

MINI FISH. A newly named species of minnow from peat swamps in Southeast Asia is shorter than the width of a fingertip. Proc. Royal Soc. B.; (fish on finger) M. Kottelat

A specimen of a mature female minnow, now named Paedocypris progenetica, from peat swamps in Sumatra measures only 7.9 millimeters long, report Ralf Britz of the Natural History Museum in London and his colleagues. They found P. progenetica females from 5.3 to 10.3 mm long, the group says in an upcoming Proceedings of the Royal Society B. The 7.9-mm fish, though, was the smallest carrying ripe eggs.

Britz says that’s shorter than the previous record-holder, the stout infantfish (Schindleria brevipinguis) from the Great Barrier Reef. The only adult female S. brevipinguis that was measured was 8.4 mm in length. If the smallest-vertebrate title can go to a male that must attach parasitically to a female, then the winner would be a Photocorynus spiniceps anglerfish, says Ted Pietsch of the University of Washington in Seattle. A mature male of this species can be as small as 6.2 mm in length, he and his colleagues reported last year. Regardless of who wins the title, these are remarkable fish, says Britz.

In P. progenetica, the bones of the skull fail to cover the brain. Also, the adult males have flanges on their pelvic fins and a hard knob of skin nearby. These might be tools for gripping a female during mating or handling eggs, the researchers speculate.

Sorting out such details could be a race against habitat destruction. Southeast Asia’s peat swamps are disappearing as oil palm plantations and shrimp farms take over the land. Many of the peat swamps that Britz and his colleagues surveyed in the 1990s for this work have already vanished.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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