Distribution of Agonostomus monticola and Brycon behreae in the Río Grande de Térraba, Costa Rica and relations with water flowThiago Cotta Ribeiro and Gerardo Umaña VillalobosFish monthly samples were made in three tributaries and in the main stream in order to study population dynamics and the influence of flow on abundance of Agonostomus monticola (Mugilidae) and Brycon behreae (Characidae) in the basin of Térraba River Basin (Costa Rica). Flow was seasonal in these rivers, with peak flow in October. Recruitment was different among the species, B. behreae recruited from January to June and A. monticola all year round with a peak in June-July and October-November. Juveniles were more abundant in smaller streams. Abundance was higher in general during low flow and low turbidity periods. The results suggest that the streams have an important role in the maintenance of both species in the ecosystem, where juveniles can use the streams as nursing habitats during their development, allowing these small streams to be considered as essential fish habitats. Also, it was determined that the increased volume and turbidity of water can significantly affect the proportion of adults and juveniles between the main river and its tributaries.Com o objetivo de estudar a biologia de Agonostomus monticola (Mugilidae) e Brycon behreae (Characidae) da bacia do rio Térraba (Costa Rica), coletas mensais destas duas espécies foram feitas em diferentes pontos da bacia. A dinâmica populacional entre as categorias de tamanho dos peixes entre três tributários e rio Térraba foram analisados, bem como a variação da abundância dos peixes de acordo com as variações do nível das águas ao longo do ano. A flutuação do nível das águas é sazonal nestes rios, com um pico máximo em outubro. O recrutamento foi diferente entre as espécies, B. behreae apresentou o recrutamento de janeiro a junho e A. monticola durante todo o ano com um pico nos meses de junho-julho e outubronovembro. Juvenis foram mais abundantes nos riachos menores. A abundância foi, em geral, maior nos períodos de baixo nível de água e baixa turbidez. Os resultados sugerem que os córregos têm um papel importante na manutenção de ambas as espécies neste sistema, onde os indivíduos jovens podem usar os córregos como habitats de refúgio e proteção durante o seu desenvolvimento, o que faz estes pequenos tributários serem considerados como um habitat essencial para essas espécies. Verificamos também que o aumento do volume e da turbidez da água pode afetar significantemente a dinâmica da proporção de adultos e juvenis entre o rio principal e seus tributários.
Characidium cacah, new species, apparently endemic to the rio das Velhas sub-basin, upper rio São Francisco basin, Brazil, is described. The new species is easily distinguished from congeners, except C. chicoi, C. helmeri, C. mirim, C. nana, C. nupelia, C. stigmosum and C. xavante, by having an incomplete lateral line and for lacking an adipose fin. The new species can be diagnosed from the aforementioned species by a series of characters, including the presence of 12 circumpeduncular scales, the isthmus completely scaled, a thin inconspicuous or dashed midlateral dark stripe, the absence of a conspicuous peduncular blotch, and humeral blotch and basicaudal spot variably marked.
We established the length–weight relationships (LWR) for 78 fish species from the São Francisco River basin, Brazil. Samples were originated from different scientific projects performed between 1993 and 2019. Fishing gears used were mainly gillnets and cast nets of various mesh sizes. Specimens varied from 0.6 to 128 cm (18.1 ± 11.8 cm) and from 0.01 to 26,900 g (317.9 ± 733.6 g). The allometric coefficient b varied from 2.509 to 3.494. For 66 species, the LWR parameters were completely novel and, for the other 12 species, are present for the first time for the São Francisco River basin.
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