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Chalceus epakros is a species of freshwater fish in the family Chalceidae, found in northern South America. It is a fairly recent addition to its genus, alongside the species C. guaporensis and C. spilogyros.

Chalceus epakros
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Characiformes
Family:	Chalceidae
Genus:	Chalceus
Species:	C. epakros
Binomial name
Chalceus epakros Zanata & Toledo-Piza, 2004

Description

Chalceus epakros bears visual similarities to other members of the genus Chalceus, like metallic scales and a vivid red or pink caudal fin, though several differences help separate it from its congeners. It has a thin stripe laterally that reaches the caudal peduncle, as well as a longer and more pointed snout.[1] It may occasionally bear humeral spots (a spot above each pectoral fin), but they are rather indistinct, especially compared to the humeral spots of C. spilogyros.[2] Its fins are a mixture of hyaline and reddish-pink, as opposed to the bright-yellow pelvic fins of C. erythrurus.[3]

Chalceus erythrurus and C. macrolepidotus may occasionally bear a similar lateral stripe to C. epakros, but theirs are broader and more indistinct.[2] It is hypothesized to be related to mating habits, and may be more prominent around mating season.[4] C. epakros' stripe is composed of chromatophores closer to the surface than that of C. erythrurus and others.[1]

Chalceus epakros is incredibly visually similar to C. guaporensis, including a thin lateral stripe, a pointed snout, and the occasional indistinct humeral patch.[4] C. epakros and C. guaporensis are also alike in that they lack a fontanel (soft, membranous spot) on the head, while the other three species have one between the frontal and parietal bone.[4] However, C. guaporensis is slightly larger, and it has 7 pelvic fin rays as opposed to eight on C. epakros.[2] C. epakros is the smallest Chalceus species, reaching 17.4 cm TL (with the caudal fin included); C. guaporensis reaches that same length in SL (without the caudal fin).[5]

Etymology

The specific name epakros is from Greek, and means "pointed at the end", in reference to the longer and more pointed snout;[1] compare Cryptocentrus epakros, the pointedfin shrimpgoby,

The genus name Chalceus comes from "chalkos", which is the Greek word for copper.[6] French biologist Georges Cuvier, who named the first member of Chalceus (C. macrolepidotus), named it this because the preserved specimen's scales were copper-colored ("sometimes golden") when preserved in alcohol, though its scales are silvery in life.[7][8]

Taxonomy

In the year 2004, Brazilian biologists Mônica Toledo-Piza and Angela M. Zanata performed a re-examination of the genus Chalceus, resulting in the nomination of not only C. epakros but its congeners C. guaporensis and C. spilogyros.[1] Upon study in 2005, C. epakros and C. guaporensis were determined to form a clade, accounting for their visual similarities, while C. spilogyros, C. erythrurus, and C. macrolepidotus share another.[4]

Previously, specimens of C. epakros had been misidentified as specimens of C. macrolepidotus and C. erythrurus; C. macrolepidotus (Cuvier) and C. erythrurus (Cope) are long-established members of the genus, having been named in 1818 and 1870, respectively.[9]

Habitat

Like the rest of its genus, C. epakros is a freshwater fish from northern South America.[10] C. epakros has the widest distribution of all Chalceus species, inhabiting the Amazon basin, the Orinoco river, and the Essequibo river.[1][6] Despite sharing a clade, C. epakros and C. guaporensis are not found in the same areas; this could either be due to competition between the species, or due to slight differences in environmental needs.[11]

Chalceus epakros and C. macrolepidotus are the only two Chalceus species known to occur in Guyana.[2]

Diet and behavior

Chalceus epakros seems to largely be an insectivore, targeting ants and wasps. In one study (Torrente-Vilara et al.), very few examined specimens had food material in their stomachs, making diet-mapping difficult.[11] This lines up with other, more thoroughly-studied Chalceus species, which target similar invertebrate spreads.[12][13]

Behaviorally, C. epakros is lacking in data. Other members of the genus are active, fast-moving, and somewhat skittish.[14][15]

References

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