Morphometric studies have been widely used to understand growth patterns, sexual dimorphism, and morphological sexual maturity in decapod crustaceans. Macrobrachium chryseus is a small-sized species associated with Amazonian blackwater environments, for which detailed biological information is still scarce. In this study, we analyzed the onset of morphological sexual maturity, sexual size dimorphism, and relative growth in M. chryseus. The onset of morphological sexual maturity was estimated at 4.4 mm of carapace length for males and 5.2 mm for females. Sexual size dimorphism was observed, with females exhibiting a larger body size than males across all analyzed structures. The analyses indicated negative allometric growth patterns for both juveniles and adults of both sexes, considering both body structures and cheliped articles. The results of this study expand the knowledge of the biology of M. chryseus and provide a basis for comparisons with congeneric species, contributing to ecological and evolutionary interpretations of freshwater shrimps in Amazonian ecosystems.
We observed large aggregations of metamorphosing individuals in Boana geographica in the lowland Peruvian Amazon of southeastern Peru. These observations were recorded in Lago Soledad (Madre de Dios, Peru) and were associated with high local abundance based on transect surveys. Tadpoles formed dense schools in aquatic habitats, and metamorphosis occurred in large numbers over short spatial and temporal scales, with thousands of individuals observed within a single site. Terrestrial surveys revealed exceptionally high densities of recently metamorphosed juveniles in the surrounding forest floor. Similar events were recorded at multiple locations around the lake over a short period. These observations suggest that large aggregations during the metamorphic period may be more widespread in this species than previously documented. Our findings provide detailed natural history information on aggregation and metamorphosis in B. geographica and highlight the need for further study of the environmental context and frequency of these events.
Non-native freshwater decapods are increasingly established in neotropical freshwater ecosystems, particularly in hydropower reservoirs. This study evaluated the mechanisms underlying the coexistence of two non-native shrimp species in the Furnas hydropower reservoir. Sampling was conducted at three reservoir sites using baited shrimp traps and gillnets. We analyzed population attributes, diel activity, and trophic interactions based on the occurrence of shrimp in predatory fish diets. Results showed that M. pantanalense was numerically dominant, characterized by smaller body size, fewer non-ovigerous females, and predominantly diurnal activity. M. amazonicum displayed contrasting population and behavioral traits, including larger body size, higher relative biomass, a predominance of ovigerous females, and nocturnal activity. These contrasting population and behavioral patterns indicate coexistence mediated by reproductive and temporal niche differentiation. Shrimp were frequently detected in the stomach contents of predatory fish species such as Trachelyopterus galeatus and Cichla piquiti, whereas Pimelodus maculatus exhibited a generalist diet with low occurrence of these crustaceans. This study advances understanding of the ecological mechanisms underlying the coexistence of non-native freshwater decapods in reservoir ecosystems, highlighting the need to incorporate invasive crustaceans into monitoring and management programs for neotropical reservoirs.
This study evaluated the population dynamics of the non-native shrimp Macrobrachium amazonicum Heller, 1862, in a tropical reservoir in southeastern Minas Gerais, highlighting its adaptive responses to environmental variation. Monthly collections and measurements of water physicochemical variables allowed the analysis of demographic classes, the relationship between carapace length and fecundity, and the estimation of growth patterns using the von Bertalanffy model. The species showed marked sexual dimorphism: females attained larger asymptotic sizes, while males exhibited higher growth rates. Fecundity was positively correlated with female body size, confirming that larger individuals contribute disproportionately to reproductive output. Seasonal fluctuations strongly influenced abundance, with peaks during the dry season and recruitment events at the transition between dry and rainy periods. A generalized linear model indicated that temperature and conductivity negatively affected abundance, whereas pH and dissolved oxygen showed no significant influence. These results suggest the ecological plasticity of M. amazonicum and its ability to persist in altered environments. The findings indicate that the studied reservoir provides favorable conditions for the establishment of this non-native population, reinforcing the need for monitoring environmental conditions and understanding demographic processes to better assess the potential ecological consequences of biological invasions in neotropical aquatic ecosystems.
