We sampled lagoon, river and forest stream habitats during the rising water, wet, falling water, and dry seasons in the lowland region of the Yasuni National Reserve in the Ecuadorian Amazon. We collected 195 species, increasing the current number of species for the Napo River basin to approximately 562. The steady rate of species accumulation per sample suggests that the fish fauna is still undersampled. Lagoon, river and forest stream fish communities are highly diverse and variable, composed of common species found within several habitats, of characteristic species found throughout the year, and of seasonally migrating species. Characteristic lagoon species were mainly the curimatids Curimata vittata, Psectrogaster amazonica, Potamorhina altamazonica, P. latior and Cyphocharax plumbeus. The characins Hyphessobrycon copelandi and Hemigrammus cf. lunatus and the catfishes Nemadoras humeralis, Pimelodella sp. C and Sorubim sp. A were characteristic river species. Characteristic forest stream species included Hoplias malabaricus, Hyphessobrycon copelandi, Pimelodella sp. B and Sternopyugus macrurus. During the dry season, lagoon and river habitats had the highest number of individuals and species, as fishes were concentrated in decreasing habitat area. In contrast, stream habitats had the highest species richness and abundance during the rising water and falling water seasons. Species collected included vital food fishes and seasonal migrants. The migratory catfishes Brachyplatystoma vaillantii, Hemisorubim platyrhynchos, Platynematichthys notatus, Platystomatichthys sturio and Sorubim lima were collected during the falling water season, which suggests that these species may begin migrating earlier than expected. These findings highlight the importance of seasonality for both adequately assessing aquatic biodiversity and for developing research and conservation programs encompassing whole river ecosystems.

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To elucidate the species of the genus Ancistrus that inhabit freshwater systems of Ecuador, cataloged lots of the Fish Collection, Museo de la Escuela Politécnica Nacional (MEPN), in Quito, were analyzed. Four species were identified: Ancistrus alga (Cope, 1872), A. malacops (Cope, 1872), A. clementinae Rendahl, 1937, and a new species that herein is described. Ancistrus clementinae inhabits aquatic systems of the Pacific slope, mostly in the Guayas River drainage. The other three species live in freshwater systems that drain to the Amazon River Basin. Ancistrus alga inhabit the northern and central portions of eastern Ecuador. Ancistrus malacops has a broad distribution from north to south, but is absent from the Santiago River. Both species occasionally live in sympatry. The new species is restricted to the Santiago River, in Morona-Santiago province. Each species has unique external morphological features and/or a coloration pattern that allow unambiguous identification, at least of males. This paper provides a description of the new species, and a re-description and images of the other three.

The fish collection from the Museum of Escuela Politécnica Nacional, Quito, Ecuador, has nine lots with 12 specimens assigned to genus Rhadinoloricaria. Specimens come from the Napo and Pastaza rivers, Amazon River basin, eastern Ecuador. One specimen matches accurately with figures and original description of Loricaria macromystax Günther, 1869, type species of Rhadinoloricaria. After 150 years, this is the first secure identification of the species, which allowed an accurate description of the genus Rhadinoloricaria, and the discovery of a new species from Ecuador, described herein. In addition, using available specimens, figures and literature, a comparative analysis on external morphology was performed among the eight species included in Rhadinoloricaria. The analysis documented significant differences between them, in some morphological external characters and in buccal ornamentation. The results suggest that the eight species can be grouped into three or four genera. Rhadinoloricaria, in strict sense, has two species. Apistoloricaria is considered a valid genus, and include the four species previously assigned to it. Rhadinoloricaria bahuaja and R. rhami do not belong to the known genera in the Pseudohemiodon group. At this time, available data suggests that both species could continue included in ‘Rhadinoloricaria’, waiting further analyses to solve their generic status. Results support the use of buccal ornamentation patterns alone or combined with some morphological characters as valuable tool for generic identification within Loricariini.

At the Fish Collection of the Museo de la Escuela Politecnica Nacional (MEPN), Quito, the specimens of the genus Pseudohemiodon were revised and three species were identified. The three species inhabit the Amazon versant of Ecuador. Chronologically the species are: P. lamina (Günther 1868) originally described from Xeberos (Jeberos), Peru; P. apithanos Isbrücker & Nijssen 1978, originally described from the Conejo River, Putumayo River system, Ecuador, and a new species described herein. The new species was caught in the Aguarico River, Napo River system, and is represented by two small sized specimens. It is distinguished from all congeners by the combination of the following characters: abdomen totally covered with small to medium-sized, irregularly shaped plates; absence of small plates, anterior to gill openings; eyes relatively small, and six to seven dark transverse bands, posterior to the dorsal-fin. Isbrücker & Nijssen (1978) indicate the presence of P. laticeps (Regan 1904) in Ecuador; however we didn’t find any specimen of this species. The specimens that could potentially be identified as P. laticeps are large sized specimens of P. apithanos. Some external morphological characters, morphometric and meristic data of analyzed specimens of P. apithanos and P. lamina are provided.