C. desquamator has a massivley-enlarged lower jaw and elongate body. © Anthony Terceira

Two highly-specialised, previously unidentified pupfishes we featured in an article a while back are officially described in the latest issue of the Bulletin of the Peabody Museum of Natural History.

The fish had been studied due to their exceptionally fast rate of morphological development (up to 51 times faster than congeners) plus the fact that they form a species flock endemic to San Salvador Island in the Bahamas whereas surrounding islands have only been colonised by the relatively widespread C. variegatus.

C. desquamator was formerly referred to as C. sp. ‘lepidophage’ or C. sp. ‘scale-eater’ because it is a specialist feeding largely on the scales of other fishes.

It can be told apart from other Cyprinodon species by possession of large supra-terminal jaws and an elongated body shape, plus the colour pattern in adult males which consists of solid black pigmentation throughout the entire body and median fins.

C. brontotheroides is a hard-shelled prey specialist. © Anthony Terceira

The new species is endemic to to six hypersaline lakes on San Salvador in all of which it is sympatric with C. variegatus (now confirmed, previously C. sp. ‘detrivore’), and in four with the other new species C. brontotheroides.

The latter was known as C. sp. ‘durophage’ prior to the new study and has evolved to prey on gastropods and ostracods with a modified jaw morphology allowing it to close its mouth with great force and crush shells.

The anterior process of the maxillary head extends up to or beyond the most anterior point on the dentigerous arm of the premaxilla with the result that its upper jaw is shorter than those of C. variegatus and C. desquamator. This skeletal extension is visible as a fleshy protuberance nearly encasing the upper jaw when retracted.

The paired nasal bones are not enlarged, but form a more acute angle (approximately 120°) with the dorsal margin of the neurocranium when compared with C. variegatus and C. desquamator.

Males of C. desquamator in their natural habitat. © Chris Martin

It also has pale or complete absence of banding on the body in both sexes and a shortened lower jaw relative to C. variegatus and C. desquamator.

C. brontotheroides also inhabits six lakes on the island and is always sympatric with C. variegatus.

This species flock is more-or-less unique within the genus, the exception being Lake Chichancanab in Quintana Roo, Mexico, which formerly contained seven endemic Cyprinodon species.

Unfortunately several of these are now extinct due to introduction of Oreochromis spp. (tilapia) and Astyanax affinis during the 1990s, and the authors warn of a similar situation on San Salvador since Oreochromis is already present in at least two water bodies.

For further information see the full, open access paper: Martin, C. H. and P. C. Wainwright, 2013.  A Remarkable Species Flock of Cyprinodon Pupfishes Endemic to San Salvador Island, Bahamas. Bulletin of the Peabody Museum of Natural History 54(2): 231–240.