The fish fauna of Rio de Janeiro has been extensively studied, resulting in a comprehensive database of species collected over more than three centuries. This study aimed to identify fish species, their locations, and compile scattered information to aid in climate action and freshwater conservation prioritization and an evaluation of the sampling effort to date, as well as to identify patterns of diversity and distribution of freshwater ichthyofauna, delineate biogeographic units, and explore similarity relationships between areas. Analyzing data from nearly 25 ichthyological collections and literature on original species descriptions revealed 346 fish species: 172 freshwaters native, 22 allochthonous, and 152 marine species. The checklist includes updated species names. The sampling effort in Rio de Janeiro is high, especially in coastal lowlands. The findings indicate that inventory work is still needed in certain areas. Five bioregions of freshwater ichthyofauna were identified, along with six major areas of higher species richness. This biogeographic assessment underscores the diverse and distinctive freshwater fish fauna in the basins of Rio de Janeiro, with well-defined biogeographic units.

Microplastics (plastic particles < 5 mm) are ubiquitous pollutants that pose the ability to carry microbiota, including pathogens. Microbial adhesion is usually a sign of pathogenicity, thus we investigated the adherent strains found on 4 mm nylon strips, which were ingested and excreted by wild fish specimens. Polymer analysis of the excreted samples shown no signs of degradation, nor have their controls, represented by the nylon strips submerged in the same water tanks. Both the ingested samples and controls presented pathogens in large numbers, revealing the fact that nylon microplastics can be physical carriers for pathogens in the aquatic environment.

Water and water habitats are essential to life and to the wellness of the communities that rely on them, as the Danube river is subject to human impact and vice versa, periodic surveys are required to determine the status of its pollution levels. In this work we used known microbiological indicators as well as physico-chemical ones to assess the ecotoxicological status of the Danube river from eleven locations partially forming the “Romanian–Bulgarian Danube Sector”. Most of the microbial communities found, and their densities, could be explained by point and diffuse sources scattered along the sector such as discharged household and farm wastewater, as well as nearby agricultural areas where fertilizers have been used and then leaked in the water stream during rainfalls. However, microbial data on non-point sources that lead to diffuse pollution of surface waters could be linked to such parameters and furthermore shown a slight correlation with the current status of fish communities.

Increased connectivity between coastal lagoons and the sea is expected to entail a greater proportion of marine species in the former. Chetumal Bay, estuary of the Hondo river into the Caribbean, had a limited access to the sea until the opening of the Zaragoza Canal. We sought changes in the fish community from 1999-2001 (just after an expansion of the canal) to 2015-2018. The same fishing gear was used, in the same localities, during all seasons. Total fish abundance and mean local richness decreased, although total abundance increased in the polyhaline zone. Diversity was greater in the oligohaline zone in 1999-2001, but in the mesohaline zone in 2015-2018. Three guilds were absent in 2015-2018: medium-sized herbivores, large piscivores, and medium-sized planktivores. Abundance of small benthivores decreased by decade; medium-sized piscivores and small planktivores became more abundant in 2015-2018 in the polyhaline zone. These changes may be due to the opening of the channel, but illegal fishing outside the bay may explain the decrease in juveniles of large piscivores, and erosion in the innermost part may be destroying important habitats. Our findings can be a reference for similar situations, as coastal development and climate change interact and affect tropical estuaries.