Astyanax cocibolca
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| Astyanax cocibolca | |
|---|---|
 | |
| Male (upper), female (lower) | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Characiformes |
| Family: | Acestrorhamphidae |
| Genus: | Astyanax |
| Species: | A. cocibolca |
| Binomial name | |
| Astyanax cocibolca Bussing, 2008 | |
Astyanax cocibolca s a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This fish is found in the Lake Nicaragua basin. It was once thought to be endemic to the lake, but its range has since been extended into nearby waterways; still, it is not particularly widespread. It is an omnivorous species that demonstrates a preference for fruit when living close to shore, but specimens living in the open waters of the lake have developed filter-feeding planktivory, which is unusual for members of the genus Astyanax.
It is closely related to another member of Astyanax found in the same lake, A. aeneus, but is smaller and more slender. The two otherwise look rather alike and have similar diets, aside from the planktivory of A. cocibolca. Before its nomination as a species, examples of A. cocibolca were also misidentified as congener Astyanax nasutus, which used to be the only other species of Astyanax known from the relevant locales.
Etymology
Astyanax cocibolca was formally described in a 2008 paper, where it was differentiated from Astyanax aeneus and Astyanax nasutus. It required differentiation from A. aeneus due to syntopy, and from A. nasutus because A. nasutus was formerly believed to be the only other species of Astyanax in the region.[2] However, there was speculation of an unidentified, nasutus-affiliated Astyanax as early as 1976.[3] Sightings of A. cocibolca have also been misidentified as A. nasutus in other records from 1987 and 1998.[4]
There are three subgenera in Astyanax: Astyanax, Poecilurichthys, and Zygogaster.[5] Of these, A. cocibolca belongs to Astyanax, based on its complete series of predorsal scales.[6] (The other two subgenera have incomplete series.)
Astyanax cobicolba has no known synonyms, and has retained its original name since description.[7]
The species name cocibolca is a direct reference to its type locality. It was originally described from Lake Nicaragua, which the indigenous people call Lake Cocibolca. The reason for the name of the genus Astyanax is less clear, as it was not made obvious in the original description, but it is an allusion to the Iliad, wherein Astyanax was a warrior and prince. This is thought to be because the scales of type species Astyanax argentatus were large and silvery in a way that could be compared to armor or a shield.[8]
Description
Astyanax cocibolca is a small and slender-bodied fish, reaching a maximum of 5.4 cm (2.1 in) SL (standard length, excluding the tail fin). The maximum depth of the body ranges from 29.1 to 36.4% of the length.[9] The lateral line has 34 to 38 scales. There are 9 or 10 dorsal-fin rays, 24 to 27 anal-fin rays (most often 25), and 10 to 14 rays in each pectoral fin. There are 17 caudal-fin rays in total; the upper lobe is smaller than the lower, and usually has fewer than 9 rays.[6] The inequality of the caudal-fin lobes can be used to tell A. cocibolca apart from similar congeners, such as Astyanax orstedii, that have caudal lobes of roughly equal sizes.[10] The mouth is slightly upturned.[9]
The coloration of Astyanax cocibolca is similar to that of many congeners, with a base silvery color and a dark midlateral stripe that extends down both sides. This stripe manifests as a dark rhomboidal blotch on the caudal peduncle and base of the caudal fin, and extends out to the margins of the median caudal-fin rays. When preserved in formalin, coloration may vary depending on how long the fish has been preserved, but the body generally gains a tan or pale-yellow undertone, and the caudal spot becomes more prominent.[2] Pigmentation of the fins is sparse, and appears to be concentrated distally.[6] Fins in some mixture of red, orange, yellow, and clear are common features in members of Astyanax.
As with many congeners, A. cocibolca has a humeral spot. In life, this is oval-shaped,[6] and it becomes more diffuse upon preservation.[2]