Panaque nigrolineatus laurafabianae, a new, commercially exploited subspecies of ornamental wood-eating pleco (Loricariidae: Hypostominae) from the Guaviare River basin in Colombia

The suckermouth armored catfish genus Panaque contains seven valid species, including the Royal Pleco, Panaque nigrolineatus, which has long been popular as an ornamental aquarium fish and was originally described from the Apure River basin in Venezuela. We examine a phenotypically distinct population of P. nigrolineatus from the Guaviare River in southern Colombia at the southwesternmost corner of the Orinoco River basin. In contrast to typically boldly striped populations from closer to the type locality of P. nigrolineatus, the Guaviare River basin population is usually boldly spotted, earning them the common name Watermelon Pleco in the aquarium fish trade. Because of the commercial popularity of this distinctive color morph, it is heavily exploited for export to the global ornamental fish trade. We find that the Guaviare River P. nigrolineatus laurafabianae is not only distinct geographically and in color pattern, but is also morphometrically diagnosable from P. nigrolineatus individuals from outside the Guaviare River basin. However, relatively subtle phenotypic differences, invariance in nuclear DNA markers, < 0.5% divergence in mitochondrial DNA markers 16S, cytb, and ND2, and the non-monophyly of Guaviare River populations prevent us from robustly inferring species-level distinctiveness of the Watermelon Pleco. We therefore propose to recognize this population as a distinct subspecies.