Nychthemeral variation in the fish assemblage at a river stretch in the western Brazilian Amazon

Abstract

Circadian activity patterns are among the most obvious and detectable biological rhythms in animals. This article aims to check the effects of nychthemeral variation on abundance, biomass, and composition of the ichthyofauna in the middle Machado River, Rondônia, Brazil. Collection took place at 9 sampling sites in Machado River, by means of fishing nets. We captured 1,320 specimens, belonging to 5 orders, 22 families, and 56 species, and total biomass of 689 kg. Characiformes had higher abundance and biomass in both periods; for nighttime, Siluriformes were the second most representative group in abundance. For nighttime, the biomass of Perciformes, Siluriformes, Clupeiformes, and Gymnotiformes were, in order, the higher. We emphasize the absence of temporal segregation in the biotope under study, but we highlight the contribution to abundance by the orders Perciformes and Siluriformes in using the environment at periods different from those cited in the literature. However, we point out that further sampling in both periods is required due to the occurrence of a small number of rare species unique to daytime (S = 12, 21%) and nighttime (S = 8, 14%). These results are significant to supplement the taxonomic inventories prior to the installation of large enterprises or environmental protection areas. alic'>seedlings.

Keywords

• Biomassa
• Ictiofauna
• Rio Machado
• Rondônia
• Segregação temporal