On a remarkable sexual dimorphic trait in the Characiformes related to the olfactory organ and description of a new miniature species of Tyttobrycon Géry (Characiformes: Characidae)

Abstract

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.

Morphology and immunohistochemistry of the olfactory organ in the bloodfin tetra, Aphyocharax anisitsi (Ostariophysi: Characidae)

“…This arrangement seemed essential to achieve the unidirectional flow of water through the olfactory cavity, as demonstrated in Anguilla anguilla , where the absence of the skin flap causes an abnormal and irregular movement of water flow (Teichmann, 1954). Unlike Abrahão et al (2019), the opening of the nose and the number of olfactory lamellae did not show any sexual dimorphism. Also, A. anisitsi belongs to the group of isosmates (Døving et al, 1977) since the presence of accessory olfactory sacs was not observed and NSCs were identified.…”

“…Given that reports on the biology of A. anisitsi are scarce (Corrêa, Hahn, & Delariva, 2009; Gonçalves, AzevedoII, MalabarbaI, & Fialho, 2005; Obando‐Bulla et al, 2013) and as there is only partial information on the olfactory system of the Characidae family (Abrahão, Pastana, & Marinho, 2019; Hansen & Zeiske, 1998; Schulte & Riehl, 1978), we aimed to fully describe the structural organization of the olfactory epithelium of bloodfin tetra using histology, immunohistochemistry and scanning electron microscopy. We focused on the morphology of the olfactory cells and the arrangement of the sensory and non‐sensory epithelium.…”

Encephalon gross morphology of the cichlid Geophagus sveni (Cichlidae: Geophagini): Comparative description and ecological perspectives

“…The olfactory bulb is sessile in G . sveni , as found in African cichlids (Huber et al ., 1997; Kotrschal et al ., 1998; van Staaden et al ., 1995), in Callichthyidae (Espíndola et al ., 2018; Pupo & Britto, 2018) and in a Characidae species (Abrahão et al ., 2019). Conversely, this feature may be stalked, as found in some Ostariophysi groups.…”

“…Regarding this, Kotrschal et al (1998) found the highest variability, but interspecific, in the forebrain (i.e., the portion of the encephalon composed of the telencephalon and the diencephalon) among African cichlids. The olfactory bulb is sessile in G. sveni, as found in African cichlids (Huber et al, 1997;Kotrschal et al, 1998;van Staaden et al, 1995), in Callichthyidae (Espíndola et al, 2018; and in a Characidae species (Abrahão et al, 2019). Conversely, this feature may be stalked, as found in some…”

A new species of Odontostilbe cope (Characiformes: Cheirodontinae) from rio Madeira basin diagnosed based on morphological and molecular data

“…The genetic distance between O. pacaasnovos and O. pequira ranged from 6.08% to 6.92%, while the intraspecific genetic distance in O. pequira ranged from 0.00% to 4.05% and in O. pacaasnovos samples is 0.00% (Table 2) (Bertelsen, 1951) or male-male detection related to cohort competition (Abrahão et al, 2019).…”