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Stout Infantfish
Schindleria brevipinguis Watson & Walker, 2004

Above and below: The preserved holotype of the Stout Infantfish (AMS I.23552-006) is a 8.4 mm standard length mature female fish caught in a plankton net between the surface and a depth 17 m, from the vicinity of Carter Reef, Great Barrier Reef, Queensland, January 1982. Note the large eggs visible through the lower side of the fish. View larger image. Photo: C. Bento © Australian Museum.

View larger image. Photo © H.J. Walker.

Line drawing of the holotype and paratype from Watson & Walker, 2004. The 8.4 mm long female holotype (A) and 6.6 mm long male paratype. Scale bar = 1 mm. View larger image. Illustration © W. Watson.

When the description of the Stout Infantfish was published in July 2004 it created huge interest in the world's media. The image shows Tom Trnski at the Australian Museum's media launch. Tom is holding a vial that contains a Stout Infantfish. View larger image. Photo: S. Humphreys © Australian Museum.

The recently described Stout Infantfish is arguably the world's smallest (and lightest) vertebrate species. The largest specimen captured to date is a gravid female that is 8.4 mm in standard length and weighs about 1 mg (one millionth of a kilogram).

This species is paedomorphic, which means that adults retain larval characters. It is an elongate fish with large eyes and a well developed caudal fin. With the exception of the eyes, this fish lacks pigmentation, and is transparent in life.

Very little is known of Stout Infantfish biology. Females reach sexual maturity by 7 mm to 8 mm in length and males mature by 6.5 mm to 7 mm. All six specimens have been found in depths of 15 m to 30 m in coral-reef lagoons in the vicinity of Lizard Island, Great Barrier Reef, Australia.

It is likely that the Stout Infantfish is more widely distributed. The first specimen was collected in 1979 by Jeff Leis during fieldwork based at the Australian Museum's Lizard Island Research Station. Since then, another five specimens have been collected by Jeff Leis. All six were used in the description of the new species.

View a map of the collecting localities of specimens in the Australian Museum Fish Collection. Scripps Institution of Oceanography and Queensland Museum have one specimen each.

Only two other species of infantfishes are currently known, S. praematura and S. pietschmanni. The Stout Infantfish differs from the other species of infantfishes by having a deeper body, fewer dorsal and anal fin rays and larger eyes. The urogenital papilla of males differs in shape from those of other Schindleria species.

The species name, brevipinguis, comes from the Latin brevis, meaning short (refers to the small size of the species) and pinguis meaning stout (refers to the deeper, broader body of this species compared with other species in the genus).

The Family Schindleriidae, which is related to gobies (Johnson & Brothers, 1993), contains tiny fishes that live in and near coral reefs. They may be the most abundant coral-reef fishes in the world, reaching abundances of seven per cubic metre in waters near reefs (Leis, 1978). A recent paper by Kon and Yoshino (2002), based on otolith rings, showed that infantfishes are very short-lived. In the Ruykyus Islands, Japan, they reach maturity in 23 to 60 days.

Fishes in this family are often called Schindler's fishes.

Related links

• Species description (pdf - 103k)
• View the 'What is the smallest species of fish?' FAQ.
• View the ' What is the second smallest species of fish?' FAQ.

Further reading

1. Johnson, G.D. & E.B. Brothers. 1993. Schindleria: a paedomorphic goby (Teleostei: Gobioidei). Bulletin of Marine Science. 52(1): 441-471.
2. Kon, T. & T. Yoshino. 2002. Extremely early maturity found in Okinawan gobioid fishes. Ichthyological Research. (49): 224-228.
3. Leis, J.M. 1978 Distributional Ecology of Ichthyoplankton and Invertebrate Macrozooplankton in the Vicinity of a Hawaiian Coastal Power Plant. PhD Thesis. University of Hawaii. Pp. 317.
4. Watson, W. & H.J. Walker Jr. 2004. The world's smallest vertebrate, Schindleria brevipinguis, a new paedomorphic species in the family Schindleriidae (Perciformes: Gobioidei). Records of the Australian Museum. 56(2): 139-142.