In recent decades, considerable attention has been devoted to endocrine disruptor chemicals (EDC) and studies on fish feminization have increased throughout the years as a key signal for aquatic environmental contamination. The input of domestic sewage into water reservoirs is common in South American countries, especially in cities that experienced rapid population growths and unplanned urbanization. This study aimed at characterizing morphofunctional parameters of the tropical fish Sphoeroides testudineus and investigating the potential occurrence and effects of endocrine disruptors in the Pacoti River (Ceará, Brazil), often considered a reference site. After collection from the field, fish were measure/weighted and desiccated for gender identification (males, females, and undifferentiated), gonadal histology, and vitellogenin expression. From the biometric analysis, undifferentiated fish showed lower weight and length than female and male fish, although no differences in the condition index were observed. The gonadal weight of undifferentiated fish was significantly lower than those of females and males. Although this pattern was observed, gonadosomatic index (GSI) showed a different pattern, with differences being observed just between males and the other two groups (females and undifferentiated). Vitellogenin (VTG) expression was detected in many mature male and undifferentiated fish, indicating endocrine disruption. In addition, several EDCs (estrone, 17α-estradiol, 17β-estradiol, 17α-ethinylestradiol, diethylstilbestrol, and estriol) were identified and quantified in sediments from the sampling site. These results were unexpected and indicative that the Pacoti River is impaired by estrogenic contamination.

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Histological techniques are a traditional and essential tool for adequately comprehending cellular morphology and physiology in several scientific fields, including ecotoxicological studies. Although bioassays generally recommend using small test organisms, based on advantages such as low maintenance costs and the possibility of a higher number of replicates, the histological process of such organisms is still challenging due to the difficulty of handling them. The present study proposes an accessible protocol for performing the histology of a biological sample of 8 mm maximum length and using histopathological biomarkers in Senegal sole larvae for ecotoxicological tests. Eight-day old larvae of Solea senegalensis obtained from breeders’ natural spawns in cultivation conditions were submitted to histological processing by an adjusted protocol comprising fixation, agarose array pre-embedding, dehydration, paraffin embedding, slides’ preparation, and image analysis by light optical microscope coupled to a digital camera. Low-cost and easy-to-use alternatives were applied in the technique execution. The histological steps were detailed, and S. senegalensis morphological features were presented. This can be considered valuable background information for ecotoxicological studies where changes in cell morphology and physiology are expected.

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Heavy metals may appear in the environment as a result of different anthropogenic activities, such as agriculture practices, industry and mining. They can reach aquatic environments as complex mixtures, and single chemical toxicity as a baseline for risk assessment can underestimate the impairment of ecosystems. The aim of the present study was to evaluate combined toxicity of binary mixtures of zinc and nickel to the tropical mysid Mysidopsis juniae. Acute toxicity was assessed and mixture toxicity was modelled using the conceptual models for concentration addition and independent action to predict whether both metals act additively or whether they interact with each other inside the organism. For that, the observed mortality data were compared with the modelled data. For the single toxicity assessment, results showed that nickel induced higher toxicity than did zinc, with lethal concentrations to 50% of the organisms of 180±30μgL–1 and 260±40μg zinc L–1 respectively. In binary mixtures, both metals acted additively and no interactions were predicted by using the conceptual models. The present study has highlighted the need to fill the gaps in toxicity studies using marine species and approaches that can help improve the assessment of accurate risk in the environment.