Mario Vinicius Condini

Introduction: Estuaries are dynamic environments that structure fish populations and can be investigated through geochemical signatures recorded in otoliths throughout the lives of individuals. Objective: This study aimed to assess the spatial geochemical differentiation of Genidens genidens, Guri sea catfish, across estuaries in southeastern Brazil using otolith elemental ratios and both univariate and multivariate approaches. Methodology: A total of 68 individuals were sampled from three estuaries (Rio Doce, Ipiranga, and São Mateus), with a subset of 53 individuals (aged 3–5 years) used for ontogenetic comparisons. Otolith microchemistry was analyzed using LA-ICP-MS, generating elemental profiles along the growth axis. Core, edge, and full transect signatures were defined. Data were analyzed using univariate and multivariate approaches, including PERMANOVA and Random Forest for spatial discrimination. Results: Geochemical signatures revealed spatial differentiation among estuaries, with a distinct separation of Rio Doce from Ipiranga and São Mateus (PERMANOVA: Pseudo-F = 20.23; p = 0.001). For individuals aged 3–5 years, no spatial differentiation was detected in the core (p = 0.184), whereas the edge showed significant separation among estuaries (p = 0.001; R² = 0.434). Random Forest achieved an overall classification accuracy of 82.35%, with the highest accuracy for Rio Doce (95.65%), and identified Ba:Ca as the most important variable (56.0%). Conclusions: The observed spatial differentiation indicates that otolith geochemical signatures reflect regional environmental contrasts among estuaries, with Ba:Ca acting as the main discriminant. The lack of differentiation in the core, in contrast to the edge, suggests that spatial signals are primarily associated with more recent life stages. The high classification performance further supports the ability of multi-elemental signatures to discriminate estuarine systems, although lower accuracy between Ipiranga and São Mateus highlights the influence of environmental similarity. Overall, otolith microchemistry proved effective in detecting spatial structure at a regional scale.

Understanding habitat use and connectivity in estuarine fishes is essential for effective conservation and management. In this study, otolith microchemistry was applied to investigate habitat use and connectivity of the estuarine catfish Genidens genidens across three estuaries in southeastern Brazil. A total of 58 individuals were analyzed using laser ablation inductively coupled plasma mass spectrometry, focusing on strontium-to-calcium (Sr:Ca) and barium-to-calcium (Ba:Ca) ratios. Variations in elemental ratios along otolith transects were used to infer individual ontogenetic patterns along the estuarine–marine gradient. Most individuals exhibited combined use of estuarine and marine environments, while trajectories restricted to freshwater were rare. The apparent complexity of chemical profiles tended to increase with age; however, this pattern disappeared after correction for size-related bias, suggesting that age itself did not significantly influence habitat-use transitions. These patterns are consistent with ecological plasticity and partial migration within populations of G. genidens, although they may also reflect exposure to variable environmental conditions. Sr:Ca ratios were useful indicators of salinity-related transitions, whereas Ba:Ca ratios provided complementary information associated with continental influence. Overall, this study highlights the applicability of otolith microchemistry for investigating habitat-use patterns in estuarine fishes and reinforces the ecological importance of estuaries for feeding, growth, and recruitment in G. genidens, while acknowledging inherent limitations related to environmental variability and proxy interpretation.

Otolith microchemistry was used to investigate habitat use and connectivity of the estuarine catfish Genidens genidens across three estuaries in southeastern Brazil. A total of 58 individuals were analyzed using laser ablation inductively coupled plasma mass spectrometry, focusing on strontium-to-calcium (Sr:Ca) and barium-to-calcium (Ba:Ca) ratios. Variations in elemental ratios along otolith transects allowed the reconstruction of individual ontogenetic trajectories along the estuarine–marine gradient. Most individuals exhibited combined use of estuarine and marine environments, while trajectories restricted to freshwater were rare. The complexity of chemical profiles increased with age, indicating more frequent habitat shifts throughout ontogeny. These patterns reveal high ecological plasticity and partial migration within populations of G. genidens. Strontium-to-calcium ratios were effective indicators of salinity-related habitat transitions, whereas Ba:Ca ratios provided complementary information associated with continental influence. Overall, this study demonstrates the applicability of otolith microchemistry to infer individual life-history pathways and highlights the role of estuaries as key habitats for feeding, growth, and recruitment in G. genidens.

We present a novel approach to structure and interpret long-term environmental monitoring data, by combining the Adverse Outcome Pathway (AOP) concept with probabilistic causal modeling. To that end, a large-scale monitoring program which assessed the impacts of the collapse of a large tailings dam in southeastern Brazil in 2015 was used as our case study. Six years of monitoring (2018–2024) across the river towards the sea provided data to integrate under our framework, including dissolved metal(loid)s, fish bioaccumulation, and sub-individual biomarkers. First, metal(loid)s quantified in the water column was integrated into an index, which characterized the environmental gradient by translating the toxic pressure from the river to the sea. Then, within the AOP framework, biomarkers of antioxidant defense, oxidative damage, and tissue injury were mapped to a growth-related outcome and integrated using piecewise structural equation mixed-effects modeling. Toxic pressure varied across the environmental gradient, being consistently higher in the river, decreasing towards the sea. Biomarker responses reflected these area-specific pressures: in the river, metallothionein, lipid peroxidation, and histopathological lesions were strongly associated with toxic pressure and specific metals, whereas in marine environments, responses were weaker and largely influenced by species or temporal variability. Notably, lesions were consistently linked to oxidative stress and, in the freshwater, negatively associated with fish condition index, suggesting that tissue-level damage can scale up to growth impairment. Overall, biomarker responses revealed both expected and unexpected patterns, highlighting the context-dependent nature of defense mechanisms under mixed-metal exposure and the value of integrated approaches to environmental monitoring.

Salmonid species have increasingly been established in South America for aquaculture and recreational fishing purposes. This study provides the first scientific record of the Chinook salmon ( Oncorhynchus tshawytscha ) in the Patos Lagoon (32°S), the world's largest choked coastal lagoon. The specimen was a female with 770 mm (total length), 3992.1 g, estimated age of 6 years and an advanced sexual maturation stage. Based on multiple tools (DNA barcoding, stable isotopes in eye lens, otolith growth layers and egg's histological analysis), we discussed potential entry routes for this species into the lagoon.