Are fish assemblages recovering after the huge disaster of mining tailing dam collapse in Mariana (Brazil-MG)?

The Doce River basin is located in the Brazilian states of Minas Gerais (MG) and Espírito Santo (ES). Anthropogenic expansion throughout the twentieth century heavily modified the bioecological configuration of the region, which was worsened in November 2015 by the collapse of the Fundão tailing dam in Mariana municipality (MG). Local ichthyofauna suffered a loss of environmental quality, which served as an alert to the possible decline of native species and transformation of fish assemblages. Through a systematic literature review, the present study aimed to investigate the recovery stage of fish assemblage after the disaster. To accomplish this, we selected 14 documents reporting species lists and fish distributions in the area principally affected by the disaster. Data collected about fish assemblage (presence/absence) were spatially (upper, middle, and lower sections) and temporally (pre- and post-disaster) arranged, followed by non-metric multidimensional scaling (NMDS) analysis to assess similarity. We applied the Analysis of Similarities (ANOSIM) non-parametric test to confirm statistically significant differences between groups. We complemented the study by searching for the main bioecological characteristics of the most frequent species raised among the selected documents. NMDS showed differences in the similarity of fish assemblages among the three spatial sections, as confirmed by ANOSIM (p < 0.05), but no differences for the temporal component were observed. Nevertheless, we detected a trend based on continental fish assemblage transformation, as determined by the presence of many non-native species in the post-disaster period, suggesting the better resilience of these species over that of native species. The missing of many native species previously easily collected, mainly from the families Characidae, Loricariidae, and Trichomycteridae, suggested the system moving toward a new condition, probably worsened than the previous one. The ichthyofauna of the estuarine environment, on the contrary, seems to have recovered faster than ichthyofauna from the continental environment.

Organization of fish assemblages in blackwater Atlantic Forest streams

This study aimed to determine whether fish species occupy different mesohabitats, as defined by specific criteria of substrate types in Atlantic Forest blackwater streams. We sampled fourteen coastal blackwater rivers along the coast of São Paulo State, Brazil, during the low-flow season (June-September/2016). For each stream, we selected three mesohabitat types (sand, leaf-litter and trunks) in a 100 m river stretch. We sampled 41 mesohabitats, 31 of which contained fish, resulting in 15 species. When multivariate analysis of variance (MANOVA) was applied to the mesohabitat abiotic variables, no significant differences were indicated between them. ANOSIM for species density and biomass and Redundancy Analyses (RDAs) for species density, biomass and fish community indexes showed similar patterns of community structure among mesohabitats. Nevertheless, fish biomass, diversity and richness were associated with such unique environmental features as low shading and shallow habitats. The observed dispersion among mesohabitats suggests that these communities are subject to some level of disturbance, which may affect the value of patches as refugia. Thus, the sharing of these mesohabitat patches among species may represent an opportunistic strategy to maximize the use of available resources for these low density populations living in these unique environments.(AU)

O objetivo do estudo foi testar se espécies de peixes ocupam diferentes mesohabitats definidos por critérios específicos de tipos de substrato em riachos de águas pretas de Mata Atlântica. Durante a estação de baixa vazão (junho-setembro/2016), foram amostrados quatorze riachos costeiros de águas pretas no litoral de São Paulo, Brasil. Para cada riacho, selecionamos três tipos de mesohabitats (areia, folhiço e troncos) em um trecho de rio de 100 m. Amostramos 41 mesohabitats, dos quais 31 com peixes, resultando em 15 espécies. A análise de variância multivariada (MANOVA) aplicada às variáveis abióticas dos mesohabitats, não indicou diferenças significativas entre estes. A ANOSIM para densidade de espécies e biomassa e as Análises de Redundância (RDAs) para densidade de espécies, biomassa e índices da comunidade indicaram padrões semelhantes da estrutura da comunidade entre mesohabitats. No entanto, a biomassa, a diversidade e a riqueza de peixes estiveram associadas a características ambientais específicas tais como habitats rasos e sombreados. Os resultados sugerem que estas comunidades estejam sujeitas a certo nível de perturbação, o que afeta o valor dos mesohabitats como refúgios. Assim, a utilização dos diferentes mesohabitats entre as espécies pode representar uma estratégia oportunista para maximizar o uso de recursos por essas populações de baixa densidade que vivem nestes ambientes peculiares.(AU)

Acute toxic and genotoxic effects of formalin in Danio rerio (zebrafish).

Formalin is a readily soluble chemical used as a sanitizing agent in the home and hospital. Formaldehyde solutions are routinely used in aquaculture for the prophylaxis and treatment of parasites and fungi, but the adverse effects of their application need to be further investigated. Danio rerio or zebrafish has characteristics favorable to its handling and breeding, and it is highly sensitive to various chemicals, being an ideal experimental model for this type of investigation. Thus, the objective of this study was to verify the toxic and genotoxic effects of formalin and to determine the lethal concentrations of this chemical to support its safe use in disinfection processes. Acute and chronic tests were performed using methods in accordance with international protocols. The genotoxic effect of formalin was evaluated with the micronucleus test using blood samples, which were collected at 96 and 192 h of exposure. The LC50-96h of formalin in D. rerio was 45.73 mg L-1, demonstrating its high resistance compared to other species. Regarding the genotoxic effect, the sublethal concentrations of formalin showed a positive correlation with micronuclei according to the increase in its concentration independent of the time of exposure. The incidence of micronuclei increased with concentration, and the addition of 1 mg L-1 formalin corresponded to an increase of 2.9% in the average number of micronuclei. In other words, formalin at even sublethal concentrations caused genotoxic effects in peripheral blood erythrocytes of D. rerio. Therefore, we recommend further studies and other tests involving this chemical for its use at environmentally safe concentrations.