Tailspot tetra
The tailspot tetra (Bryconops caudomaculatus) is a freshwater fish that lives in the coastal river regions of upper South America. Both its common and scientific names reference the distinct spot of color present on the tail fin, which is one of its defining characteristics. It is a small fish, reaching 4.8 in (12.4 cm) at its longest. Despite its small size, it is an active swimmer, with a preference for fast-flowing waters.
The tailspot tetra, like the rest of the genus Bryconops, has a slender body described as "smelt-like", similar to members of sister genus Piabucus.[1] It reaches 4.8 in (12.4 cm) in total length (with the tail fin included), and a corresponding weight of 20.1 grams.[2] Its back scales are tinted orange to dark-orange, fading into silver on the belly when the fish is alive. Upon close inspection, the scales are also revealed to have a scattering of minute dots.[3]
The spot of bright orange on the basal half of the caudal fin is what gives the tailspot tetra its common name. The scientific name also reflects this - "caudo-" is in reference to the caudal fin (the tail fin), and "-maculatus" means "spotted" (compare with the word "immaculate", which means "without blemishes").[4] Though it is more vivid in life, this spot of color may turn pale upon preservation of a given specimen.[5]
Visually, the tailspot tetra is easy to confuse with congeners B. magoi and B. collettei, which means that they have often been misidentified as B. caudomaculatus.[6] (This is part of the reason they are considered to be in the same species complex.) Recent congener B. florenceae was also previously misidentified as B. caudomaculatus before its distinction as a separate species.[7]
The lateral line is usually incomplete. Some specimens of B. caudomaculatus display a particularly truncated lateral line that makes them appear more visually similar to B. durbini.[5] Another recently named congener, Bryconops piracolina, is visually similar, but with a difference in the lateral line - it has a smaller number of pored lateral line scales than B. caudomaculatus.[8]
In 1864, Albert Günther gave the tailspot tetra the scientific name Tetragonopterus caudomaculatus when he first described it as a new species.[9] The genus Tetragonopterus is closely related to the genus Bryconops, and therefore an element of viability remains in Günther's original placement.[5] Ichthyologist Carl H. Eigenmann placed B. caudomaculatus into the genus Creatochanes, which was later classified as a subgenus of Bryconops, to which B. caudomaculatus no longer belongs; Instead, it is considered Bryconops (Bryconops) caudomaculatus.[5][10]
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