Fish assemblages in Rodrigo de Freitas Lagoon, Rio de Janeiro, Brazil: Who remains after years of transformation?

Resumo

Rodrigo de Freitas Lagoon (RFL) has undergone intense environmental changes in recent decades, driven by accelerated urbanization, domestic sewage discharge, and hydrodynamic alterations. This study investigated the current composition of fish assemblages in RFL, with an emphasis on life history strategies, seasonal variations, and environmental influences. A total of 36 species distributed across 20 families were recorded, with a predominance of opportunistic species such as Phalloptychus januarius, Jenynsia lineata, and Geophagus brasiliensis, which are well adapted to unstable and degraded environments. Comparisons with historical data revealed a marked loss of diversity: of the 64 species recorded between 1991 and 2004, only 13 remain, indicating a process of ecological simplification. Seasonal analysis revealed higher species richness and abundance during summer and winter, associated with pronounced seasonal variations in water transparency, dissolved oxygen, and chlorophyll concentration. The absence of significant differences among sampling sites suggests environmental homogenization, likely resulting from limited water renewal and the intensification of anthropogenic impacts around the lagoon. Environmental variables, particularly salinity and water transparency, played a key role in shaping the fish community structure and the distribution patterns of Brevoortia aurea, Brevoortia pectinata, Poecilia vivipara, and Phalloptychus januarius. The resilience of opportunistic species such as Poecilia vivipara and Phalloptychus januarius contrasts with the presence of species exhibiting Periodic or Equilibrium life-history strategies, including Micropogonias furnieri, Mugil liza, Centropomus spp., Diplodus argenteus, and Caranx spp. The persistence suggests that marine influence still occurs, especially in areas closer to the tidal channel. These findings indicate that, although RFL still supports species of ecological and fisheries importance, its biodiversity continues to decline, compromising ecosystem resilience and fisheries sustainability. Our results highlight the urgent need for effective conservation and management strategies tailored to urban lagoon systems.