Iguanodectes spilurus

Iguanodectes spilurus is a small fish, reaching a maximum of 10.2 cm (4.0 in) in standard length (SL).[1] Based on hobbyist reports, captive specimens, or specimens for sale in the trade, more often reach a maximum of roughly 5 cm (2 in).[2][3] Its body is silvery in color, its fins are largely translucent, and it lacks a red lateral stripe (which is seen in multiple other members of the genus).[4] Instead, its lateral-line scales are reflective green in color, which is the origin of one of its common names - "green-line lizard tetra". The base of its caudal fin sports a distinct black spot.[5]

Iguanodectes is generally a complex genus in terms of morphology, both interspecies and intraspecies, and I. spilurus is an example of this. Ichthyologist Jacques Gery considered it a polymorphic species (i.e. a species that has multiple documented different appearances or forms), though acknowledged uncertainty regarding the causes and mechanisms therein.[6] Several comparative factors can help differentiate it from similar congeners, including its number of lateral-line scales (60-64) and predorsal scales (24).[7]

All members of Iguanodectes are narrow-bodied and shallow-chested, lacking the deep chest seen in sister genus Piabucus. The pectoral fins are also shorter in Iguanodectes.[8]

Iguanodectes spilurus was originally described as Piabuca spilurus by German-British zoologist Albert Günther in 1864.[10] American ichthyologist Edward Drinker Cope later described it as Iguanodectes tenuis in 1872, under the impression that he was studying a separate species entirely;[11] this was possibly due to the varying coloration of I. spilurus.[6] I. tenius and P. spilurus were synonymized by American ichthyologist James Erwin Böhlke in 1954, with input from Ethelwynn Trewavas, a fellow ichthyologist. Its generic placement within Iguanodectes, a novel genus upon nomination of I. tenuis, was deemed correct based on morphological features, but spilurus became the accepted specific epithet, as it was established prior.[12]

Böhlke also considered Iguanodectes rachovii synonymous with I. spilurus,[12] but this is rejected by modern ichthyologists. I. rachovii is considered its own species.[13]

Iguanodectes spilurus is known from the Amazon, Essequibo, Orinoco, and Tocantins river basins; thus, it is the most widespread member of Iguanodectes.[4] It demonstrates a preference for rocky substrate and flowing water, though it is found in both blackwater (slow-moving) and clearwater habitats.[1][16][17]

Iguanodectes spilurus is omnivorous, and is a visual animal, using sight to pursue prey (as opposed to a mechanism like sensory barbels).[16] Along with invertebrates, it also eats algae, leaf litter, and detritus.[17] It seems to be easygoing by nature, living in sympatry with various other fish species within its native range (including congeners I. geisleri and I. polylepis).[6]

Iguanodectes spilurus is subject to infection by parasitic nematode larvae of several genera that colonize various internal organs and bodily systems. The liver appears to be the most susceptible to damage from parasitic activity.[18]

Iguanodectes spilurus has not been evaluated by the IUCN.[1] However, its range spans several river basins and countries therein, which provides a stable basis for its population.[4] Its wide range also indicates an ability to adapt to changes in its environment (at least to an extent). Therefore, it is unlikely to face immediate threats of endangerment or extinction.