Iguanodectes purusii

Iguanodectes purusii is a small fish, reaching a maximum of 7.5 cm (2.9 in) standard length (SL).[1] Iguanodectes as a genus is generally shallow-chested and narrow-bodied, with short pectoral fins, and I. purusii is no exception to this.[2] The anal-fin origin is slightly posterior to the middle of the body, the dorsal fin the same, and the fins are largely hyaline (clear).

Many members of Iguanodectes have a base scale color that is yellow to yellowish-silver, but I. purusii more frequently demonstrates plain silver;[3][4] nonetheless, it may be confused with congener Iguanodectes geisleri, as both species have a lateral-line stripe in three colors (red, yellow, and black, from top-to-bottom).[5] I. purusii is noted to be particularly similar in coloration to congener Iguanodectes spilurus. There is a patch of dark pigmentation on the junction of the caudal-fin lobes that extends onto the upper lobe, not dissimilar to related species Bryconops melanurus. The lateral stripe is rather narrow.[6]

Upon description by Austrian zoologist Franz Steindachner in 1908, I. purusii was assigned the baisonym Piabucus purusii.[7] In later publications (1970 and 1993), French ichthyologist Jaqcues Géry reassigned it to the genus Iguanodectes based upon the differences in body shape. Géry speculated that Steindachner considered all similar species to belong to Piabucus, and declined to include Iguanodectes in relevant taxonomical study.[6]

A species from the related genus Bryconops, Bryconops transitoria, continues to undergo taxonomic evaluation to this day, and an examination of some of the earliest collected specimens revealed that one of them was actually a specimen of I. purusii. It is unlikely that this was a case of mistaken identity, as the responsible scientist (Steindachner) had described both species; more likely, it was the result of a simple mis-label.[8]

Iguanodectes purusii was first described from the Purus river basin of Brazil.[9] In modern times, its range is known to encompass the Purus, Amazon, Madeira, Guaporé, and Pastaza rivers, including various tributaries.[10] Though little is known of specific biotope preferences, I. purusii has been documented to stay near the surface of the water.[2]

Iguanodectes purusii is largely herbivorous, occasionally feeding on insects that make their way into the water from outside.[2] This is in line with Iguanodectes as a genus, which is composed mostly of herbivores.[11] Little is known of the ecology of Iguanodectes, though limited observations exist of several species in aquaria, including I. purusii.

Iguanodectes purusii has not been evaluated by the IUCN.[1] Its type locality, the Purus river, is under environmental pressure from anthropogenic sources that include deforestation and agricultural development.[12] The lattermost factor has a documented negative effect on water quality, including increased levels of pesticides and fecal contamination.[13] Nonetheless, I. purusii has a broad range that encompasses a good handful of river basins; thus, its population is likely to remain stable.