Mariana Costa Fratari

Local and regional species diversity is influenced by historical factors, resource availability, biotic interactions, the presence of resources, and adequate environmental conditions. We evaluated the effects of local environmental variables and spatial structure on fish species richness and composition along sandy beaches of a Neotropical river. The sampling period extended from June to September 2017, encompassing 31 sandy beaches. A comprehensive collection effort yielded 15,627 individuals representing 60 distinct fish species. The PCA indicated that beaches located in the upper part of the river tended to have higher pH, current speed, and shallower depth, while the lower part had greater length, warmer waters, and greater concentration of dissolved oxygen. There was a trend towards lower species richness in the upper part and greater richness in intermediate portions of the Acre River. Multiple regression indicated that only water temperature positively influenced the variation in fish species richness as predicted by the energy‐environment hypothesis. Also, water temperature, concentration of dissolved oxygen, and depth were essential to determine changes in species composition. We found no evidence of spatial autocorrelation. Therefore, local environmental variables, especially the water temperature, are important factors in determining the fish richness and variation in species composition on sandy beaches of the Acre River.

This study evaluated the length-weight relationship (LWR) and the relative condition factor (Kn) of 11 fish species in streams of the São Francisco Igarapé Environmental Protection Area (APA), located in the Acre River Basin, Amazon. LWR is an essential tool for assessing growth, body condition, and biomass of fish populations, reflecting aspects of species' well being. Additionally, the relative condition factor (Kn) is a crucial parameter for indicating the physical state and health of species, reflecting the amount of energy accumulated relative to size. The research revealed that the growth coefficient (b) ranged from 2.65 to 3.33, indicating predominantly isometric growth in several species, where weight gain parallels length growth. Fish were collected at seven sampling points using active search methods. Results showed that most species exhibited isometric growth, with Kn values ranging from 0.71 to 1.4, with 8 species showing Kn values greater than 1. These results suggest that the São Francisco Igarapé APA provides favorable conditions for fish growth and health, although some species showed variations in growth and well being indices, possibly due to environmental pressures. This study contributes to the understanding of the biological dynamics of fish populations in the region and provides valuable information for the management and conservation of species in protected areas of the Amazon.

We analyzed the length-weight relationships of 12 lesser-known fish species sampled in four streams in the Southwestern Amazon, in Acre State, Brazil. Diurnal and nocturnal sampling took place in four streams in 150-meter sessions in March and November 2017. Linear regression was applied using the least squares adjustment method. In total, 867 specimens were collected, representing four orders, ten families, and 12 species. The b coefficient of the length-weight regression ranged from 2.58 to 3.22, and r2 from 0.77 to 0.99. Five species had negative allometric growth (b < 3), six had isometric (b = 3), and one had positive allometric growth (b > 3). The length-weight relationship was documented for the first time in 10 of the 12 species – Chrysobrycon hesperus, Knodus smithi, Phenacogaster pectinata, Carnegiella myersi, Pyrrhulina obermulleri, Gymnotus curupira, Brachyhypopomus sullivani, Corydoras cervinus, Denticetopsis seducta, and Bujurquina syspilus. Our results contribute to the knowledge on life cycle parameters of fish species from the Southwestern Amazon.

Few studies have investigated the ichthyofauna of streams in the upper Purus River basin, hampering efforts to understand the diversity of these numerous bodies of water. This study presents the first inventory of the ichthyofauna in the upper Purus-Antimary interfluve, southwestern Amazonia. The study was based on data compiled from various sources, including online repositories, scientific articles, and fish collected from four streams in a protected area. We assessed species richness, distribution area, conservation status and anthropogenic threats. The fieldwork study was carried out in four "terra firme" streams in the Purus River basin, with fieldwork conducted during the rainy season in March and November 2017. We identified a total of 92 species, 26 families, and six orders. The order Characiformes exhibited the highest species richness with 42 species, followed by Siluriformes with 34, and Gymnotiformes with 8 species. The Characidae family was the most diverse, with 25 species, followed by Loricariidae with 11 species and Callichthyidae with seven species. The collected fish samples totaled 1,794 individuals representing 58 species, 22 families, and 4 orders. The most abundant species were Knodus smithi with 307 individuals, followed by Chrysobrycon hesperus with 247 and Tyttocharax madeirae with 165. Most species were classified as being of low conservation concern. The study expanded the known extent of occurrence for Anablepsoides hoetmeri to 2,163.777 km². Our findings underscore the importance of conserving aquatic habitats and riparian vegetation within the upper Purus-Antimary interfluve, given the presence of a rich and restricted ichthyofauna. Furthermore, we highlight the significant risks posed by anthropogenic pressures such as deforestation for pastures, wildfires, and illegal fishing activities.