Among the order Characiformes, secondary sexual dimorphism is commonly associated to the occurrence of bony hooks on fins, shape and length of the dorsal and anal fins, and sexual dichromatism. The analysis of a new miniature Characidae species of the genus Tyttobrycon, described herein, yielded to the discovery of a sexually dimorphic trait related to nostril aperture and number of olfactory lamellae. In this type of dimorphism, mature males present larger nostril aperture and higher number of olfactory lamella than females. A dimorphic olfactory organ is for the first time recorded and described for a member of the Characiformes. Gross morphology and development of brain and peripheral olfactory organ of Tyttobrycon sp. n. are described and compared to other species of Characidae. It is hypothesized that such dimorphic trait is related to male-male detection during cohort competition in small characids. The new species of Tyttobrycon is diagnosed from its congeners by the number of branched anal-fin rays (19–21) and the absence of a caudal-peduncle blotch. It occurs in a small tributary of Rio Madeira basin, near to the limit between Brazil and Bolivia, Acre State, Brazil.

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Crenuchinae is a subfamily of the fish family Crenuchidae distributed in the Amazon Basin with pronounced sexual dimorphism and exuberant colour patterns. Recent fieldwork in the tributaries of the Rio Aripuanã drainage, a large tributary of the Rio Madeira (Amazon Basin), resulted in the discovery of two distinctive, undescribed species of the crenuchin genus Poecilocharax, which are formally described herein, combining morphological and molecular data. These are the first representatives of Crenuchinae discovered after a gap of 57 years and the first records of Poecilocharax from the tributaries of the right bank of the Rio Amazonas draining the Brazilian crystalline shield. Based on a taxonomic review including all species of the subfamily, we provide an expanded morphological diagnosis for Crenuchinae. This now includes characteristics related to the lateral-line canals of head and body, the number of dorsal-fin rays and sexually dimorphic traits. In addition, we review previous characteristics used to diagnose Crenuchus and Poecilocharax, providing comments on their polarity and distribution across the subfamily. A dichotomous key is provided for the first time for species of Crenuchinae.

We describe the first recorded association between fishes and nudibranchs in epipelagic waters. In situ observations and photographs of a juvenile spotted driftfish Ariomma regulus (Stromateiformes; Ariommatidae) swimming alongside the planktonic nudibranch Phylliroe lichtensteinii (Gastropoda; Phylliroidae) were made during blackwater scuba dives off Palm Beach, Florida, United States of America. In this paper, we describe this behavior, highlighting a previously undocumented zooplanktonic host used by fishes. This finding also demonstrates the importance of community science in advancing our understanding of the early life history of marine species.

The division Percomorphacea encompasses a major fraction of the extant fish diversity, including over half of all known ray-finned fishes and approximately one fourth of the living vertebrates. The interrelationships among the major percomorphacean lineages are still far from a satisfactory resolution. Among the 30 percomorphacean orders, Stromateiformes encloses 77 extant species distributed into 16 genera and six families -Amarsipidae, Ariommatidae, Centrolophidae, Nomeidae, Stromateidae, and Tetragonuridae. Members of this order are globally distributed in temperate and tropical oceans and exhibit two extraordinary morphological specializations: the presence of a pharyngeal sac and of a subdermal canal plexus over the head and trunk. The phyletic status of Stromateiformes has never been adequately tested on morphological grounds and the monophyly of the order has been recently rejected by multiple molecular analyses. Moreover, stromateiforms have been indecisively aligned with disparate percomorphacean taxa by both morphology-and molecular-based studies. The present work delved into these questions and presented a comprehensive phylogenetic revision of Stromateiformes based on an exhaustive analysis of 218 phenotypic characters and 66 terminal taxa encompassing all valid stromateiform genera, as well as all percomorphacean families somehow aligned with stromateiforms in prior studies. The resulting topology retrieves the order as monophyletic, supported by four unequivocal synapomorphies. Amarsipidae, the only stromateiform lacking a pharyngeal sac, is resolved as the sister group of the remaining members of the order. Centrolophidae is not monophyletic, with five of its genera grouped into a basal clade, whereas the other two appear as successive sister groups of a clade containing the remaining stromateiform families. All these families are recovered as monophyletic with the following cladistic arrangement: Nomeidae (Stromateidae (Tetragonuridae, Ariommatidae)). A clade composed by Bramidae and Caristiidae is herein hypothesized the sister group of stromateiforms, although this arrangement is supported by only a single unequivocal synapomorphy. The present study further hypothesizes that the remarkable symbiotic relationship between juvenile stromateiforms and gelatinous invertebrates (e.g. medusa and salps) is probably associated with the evolution of some of its most remarkable morphological specializations, such as the presence of dendritic pyloric caeca, subcutaneous canal plexuses, and the pharyngeal sac. ABE T. 1954-1955 or uncommon fishes from Japanese waters. V. Notes on the rare fishes of the suborders Stromateoidei and Tetragonuroidei (Berg). Japan Journal of Ichthyology, 3: 113-118. AHLSTROM EH, BUTLER JL, SUMIDA BY. 1976. Pelagic stromateoid fishes (Pisces, Perciformes) of the eastern Pacific: kinds, distributions, and early life histories and observations on five of these from the northwest Atlantic. Bulletin of marine science, 26(3): 285-402 ALLEN GH. 2001. The ragfish, Icosteus aenigmaticus Lo...

This article is a redescription of Pimelodella longipinnis, an enigmatic catfish previously known only from its holotype and with uncertain type locality. The species is redescribed based on recently collected materials from streams of the Mata Atlântica bioregion, in Santos municipality, São Paulo State, Brazil. Pimelodella longipinnis is assigned to a putatively monophyletic group, the Pimelodella leptosoma-group, diagnosed by the presence of a supraoccipital process not reaching the anterior nuchal plate, with a gap of ca. 20-25% of the supraoccipital process total length, and whose tip notably surpasses the midpoint of the complex vertebra in dorsal view. We also present a list of fish species described from a shipping sent to the American Museum of Natural History from the former Museu Paulista (now Museu de Zoologia da Universidade de São Paulo), of which P. longipinnis was part.

Creagrutus nigrotaeniatus n. sp. is described from the rio Juruena basin, upper rio Tapajós system, Mato Grosso State, Brazil. Creagrutus nigrotaeniatus differs from its congeners by having the dentigerous surface of the premaxilla longitudinally elongate from ventral view, 4-5 post-anal scales and 2-4 maxillary teeth. The new species also has the anterior margin of hyomandibula straight or slightly concave which is a unique condition within the genus, and possesses a series of non-exclusive osteological modifications (e.g. medial opening of the dentary foramen located distinctly anteroventral to the tip of Meckel's cartilage; anterior portion of the laterosensory canal segment in first infraorbital terminating distinctly posterior to the anterior margin of this bone; presence of the third posttemporal fossa within the epioccipital; one epural present). A comparison with Caiapobrycon tucurui is provided and the placement of the new species within Creagrutus and its close relationship with C. cracentis, C. gephyrus, and C. maxillaris are discussed.