Guyanancistrus nassauensis

Guyanancistrus nassauensis is a small-sized species, the largest specimen observed having a standard length (SL) of 61.0 mm. Head and body dorsoventrally depressed and wide. Dorsal profile gently convex from snout tip to dorsal-fin origin, usually more flattened posterior to orbit, slightly convex and sloped ventrally from dorsal-fin origin to adipose fin, then slightly concave to procurrent caudal-fin rays, and rising to caudal fin. Ventral profile flat from snout to base of caudal fin. A low median ridge from tip of snout to nostrils, sometimes bordered by lateral depression, a slight elevation anterior to orbits, supraoccipital slightly convex to flat. Dorsal margin gently flattened from base of first branched dorsal-fin ray to base of adipose fin between very slight ridges formed with lateral plates of dorsal series. First lateral plates of mid-ventral series forming low lateral ridge. Caudal peduncle roughly ovoid in cross section, flattened ventrally, and more compressed posteriorly. Large, rounded and laterally flattened snout. Eye relatively small. Large oval mouth, lower lip wide, not or just reaching pectoral girdle, upper lip narrower. Lips forming an oval disk, covered with short papillae. Presence of a single narrow buccal papilla. Very short maxillary barbel. …

Guyanancistrus nassauensis is known solely from Paramaka Creek and some of its tributaries, Marowijne River Basin, in the Surinamese Nassau Mountains (an area of approximately 20x20 km2). In Paramaka Creek, G. nassauensis occurs syntopically with juvenile G. brevispinis and with Harttiella crassicauda, a second endemic species from the Nassau Mountains. However, G. nassauensis occurs both on the plateau in perennial flowing headwaters and in the upper mainstem of Paramaka Creek (lower slopes of the plateau; altitude range 120–530 m amsl), whereas H. crassicauda only occurs on the plateau proper (230–530 m amsl). In the IJs Creek tributary of Paramaka Creek on the Nassau plateau (467 m amsl) both G. nassauensis and H. crassicauda occur in cool, shallow, clear water with low conductivity, neutral pH, low inorganic N, relatively high organic N, low total P and high organic C. The bottom substrate is gravel with boulders and bedrock (with the red filamentous algae Batrachospermum sp. attached to it) and near the edge of the plateau in slightly deeper water (approximately 50 cm) stands of the emergent macrophyte Thurnia sphaerocephala occur. Its dwarfism could be an adaptation to small streams, with cool water temperature, a low productivity. In the upper mainstem of Paramaka Creek, as well as in some upstream branches on the plateau, G. nassauensis occurs syntopically with G. …

Apart from its habitat, few informations are available on the ecology of Guyanancistrus nassauensis. Few traits of its behavior were described from observations in aquarium of four specimens which were kept with Harttiella crassicauda in April 2006. G. nassauensis was active both during the day and at night, and did not retreat in shelter, even for an individual that was transferred to a larger tank with numerous other fishes. It was not territorial but tolerated the presence of other fishes, either conspecific or not. G. nassauensis mostly spent its time on the aquarium panes and on macrophytes, woody debris and rock, but not on the sandy substrate on the bottom. In aquarium, it accepted vegetarian flakes after a short period of acclimatation, and was also observed feeding on algae.