Barbel development associated to aquatic surface respiration in Triportheus signatus (Characiformes: Triportheidae) from the semiarid Caatinga rivers
2020
de Freitas Barros Neto, Luciano | Frigo, Rafael Gomes | Gavilan, Simone Almeida | de Moura, Sérgio Adriane Bezerra | Lima, Sergio Maia Queiroz
In tropical regions, limestone aquatic environments of the Caatinga are more prone to hypoxia due to water heating, long drought periods, and high rates of organic decomposition. To circumvent this limitation, some fish species have developed different adaptations to maximize oxygen capture. These adaptations usually involve the capture of oxygen on surface layers, a mechanism known as aquatic surface respiration (ASR). In Characiformes, adaptations for ASR are related to the development of labial protuberances, which may appear within a period of up to 24 h. Some species of the genus Triportheus present barbels on the lower lip, a remarkable adaptation that assist in ASR. One of these is T. signatus from the Caatinga river basins that present intermittent flow regime. This research aimed to investigate the morphology and histological organization of the barbels developed by T. signatus in a lentic environments. Specimens from semiarid drainages belonging to the Mid-Northeastern Caatinga, Maranhão-Piauí, and São Francisco ecoregions were examined. Transverse and longitudinal histological sections of different portions of the barbels were made. The histological organization of the structure shows that the barbel is very vascularized, suggesting a modification to improve gas exchange. The superficial vessels present hemosiderin extravasation, representing hemorrhagic areas, probably related to the rapid formation of the structure, indicating the fast response of this species to environmental modifications. These results suggest that the barbels in T. signatus might both assist in directing superficial water to the mouth, as well as in oxygen absorption, however this latter assumption should be tested through experimental studies.
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