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. 2006 Apr 22;273(1589):895-9.
doi: 10.1098/rspb.2005.3419.

Paedocypris, a new genus of Southeast Asian cyprinid fish with a remarkable sexual dimorphism, comprises the world's smallest vertebrate

Maurice Kottelat  1 , Ralf Britz, Tan Heok Hui, Kai-Erik Witte
Affiliations

Paedocypris, a new genus of Southeast Asian cyprinid fish with a remarkable sexual dimorphism, comprises the world's smallest vertebrate

Maurice Kottelat et al. Proc Biol Sci. .

Abstract

Paedocypris is a new genus of paedomorphic cyprinid fish from highly acidic blackwater peat swamps in Southeast Asia. It includes two new species, one of which (Paedocypris progenetica) appears to be the smallest fish and vertebrate known, with the smallest mature female measuring a mere 7.9 mm. Paedocypris has many 'larval' features typically associated with paedomorphic fish (e.g. narrow frontals that leave the brain unprotected dorsally by bone and a precaudal larval-fin-fold), but, uniquely among fishes, males also possess highly modified pelvic fins with hypertrophied muscles and a keratinized pad in front of the pelvic girdle, which, we hypothesize, function together as a clasping or holding device, thereby suggesting an unusual reproductive mode. Unfortunately, habitat destruction jeopardizes the survival of these fishes and thus opportunities for further research.

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Figures

Figure 1
Figure 1
Living Paedocypris progenetica, CMK 18496, (a, b) male, ca 9 mm; (c) female, ca 8.8 mm.
Figure 2
Figure 2
(a) Paedocypris progenetica holotype male, MZB 5998, 8.6 mm; arrow points to keratinized abdominal knob; (b) Paedocypris progenetica paratype female, ZRC 43199, 8.0 mm; arrow points to preanal larval-fin-fold; (c) Paedocypris micromegethes holotype male, ZRC 49869, 10.4 mm; arrow points to genital papilla; (d) paratype female, BMNH 2004.11.16.1-40, 10.0 mm.
Figure 3
Figure 3
(a) Paedocypris micromegethes, paratype male, ZRC 49869, 10.4 mm; pelvic fins, anteroventral view, showing hook and flange on anterior ray. (b) Paedocypris micromegethes, paratype, male, BMNH 2004.11.16.1-40, 10.9 mm, ventrolateral view on hypertrophied pelvic arrector and abductor muscles marked by asterisk symbols. (c) Paedocypris progenetica, paratype male, ZRC 43199, 8.5 mm, scanning electronic micrograph of pelvic region in ventrolateral view, arrow points to keratinized prepelvic knob.
Figure 4
Figure 4
Paedocypris micromegethes, cleared and double stained paratype, male, BMNH 2004.11.16.41-60, 10.7 mm, cartilage in blue, bone in red, note largely cartilaginous roofless skull, haemal spines on abdominal vertebrae and hypertrophied basipterygium of pelvic girdle.
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References

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