Iguanodectes purusii

Iguanodectes purusii is a small fish, reaching a maximum of 7.5 cm (2.9 in) standard length (SL). Iguanodectes as a genus is generally shallow-chested and narrow-bodied, with short pectoral fins, and I. purusii is no exception to this. 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; 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). 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.

Sexual dimorphism. The sexual dimorphism of I. purusii is minor. There are no morphometric or coloration differences, but males may or may not demonstrate small hooks on the anal fin-rays during certain months of the year, specifically November.

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

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

Presence and behavior in aquaria. Though rarely imported for trade, several members of Iguanodectes are known in the aquarium industry. I. purusii is uncommon, but is noted to be a peaceful inhabitant of community tanks, and prefers living in groups of 5 to 10 individuals. Aquarists warn of a general sensitivity to surroundings during transport and during acclimation to a new environment.

The specific name "purusii" originates from the type locality, the Purus river. "Iguanodectes" was not given a specific meaning in the publication of origin, but modern etymological evaluation concludes that the likely bases are "iguana", the lizard, and "dectes", meaning bite or tooth, in reference to the "lizard-like" dentition.