Mercury is an element with potential risk to fish and those who consume it. Thus, this study aimed to determine the levels of total mercury (THg), carry out a health risk assessment related to the consumption of the freshwater stingrays Potamotrygon motoro, and determine the physical and chemical properties of the water where stingrays occur. Stingrays of the species P. motoro were obtained from the Amazon River, and samples of the animals’ musculature were collected to determine THg levels. Risk assessment was conducted using pre-established formulas of estimated monthly intake (EMI), maximum monthly intake rate (IRmm), and hazard quotient (HQ). Three population scenarios were evaluated, considering both sexes and differences between rural and urban areas. There was no relationship between weight and THg concentration nor between total length and THg concentration. Higher EMI values were observed in rural children; for the IRmm, male children had the lowest consumption levels. For the hazard quotient, there was a similarity between the three age groups when comparing the male and female sexes. In addition, the representatives of the rural area always had lower values than the urban area. Freshwater stingrays, like other elasmobranchs, can be crucial animal species because they act as sentinels in studies that assess harmful chemicals like mercury.

Photoperiod is considered an environmental factor that influences reproduction and the growth processes of fish throughout the year. In the present study, we subjected dusky grouper Epinephelus marginatus to different photoperiods in order to evaluate growth and survival. Juvenile dusky grouper were randomly distributed in twelve 100 L tanks containing four fish per aquarium. The fish were exposed to continuous light, normal photoperiod or continuous darkness for 50 days. Fish were fed 3% of their total biomass, twice a day, and the diet consisted of ground commercial dry pellets (42% crude protein, 12% humidity, 9% ether extract, 15% mineral matter, 4% crude fiber, 3.5% calcium and 3% vitamin C, in accordance with the manufacturer’s instructions). There was no mortality during the experiment. After 50 days, the best performance was found for exposure to continuous light (24 h artificial light). The final weight of the fish reared under continuous light was significantly higher than that of the fish exposed to continuous darkness. The specific growth rate of the fish exposed to continuous light was significantly higher than that of the fish exposed to the natural photoperiod and to continuous darkness. Modifications to the photoperiod can be a key factor in increasing the efficacy of current production and the improvement of current aquaculture protocols.

The Amazon region has the largest diversity of freshwater stingrays; however, there are still places where information about this group is scarce. The present work aims to record the occurrence of freshwater stingrays in the Uatumã river basin, Amazonas, Brazil. For this, collections were carried out in three municipalities bathed by the Uatumã River, Presidente Figueiredo, Itapiranga, and São Sebastião do Uatumã. The rays were collected through fishing using a hand net and, after capture, were identified through the pattern of the dorsal and ventral color of the disc, the absence or presence of the labial groove, and the organization of the row of spines on the tail, and were also measured, weighed, and sexed. In total, 69 specimens of Potamotrygonines were captured, 59 of which were from the genus Potamotrygon and ten individuals from the genus Paratrygon. The present study provides preliminary information on the characteristics of freshwater stingray species that may occur in the Uatumã River. Furthermore, new research is necessary to improve the identification of specimens to determine the diversity and elucidate aspects related to the biology of elasmobranchs in the Uatumã River Basin, Brazil.

Amazonian fishes, as an adaptive form to the annual flood cycle, develop physiological strategies to adjust to variations in their habitats. The results of this study help to understand how freshwater stingrays adapt to changes in river levels and allow us to predict the physiology of blood and water properties in situations of extreme droughts and floods in rivers. This study aimed to evaluate the physiological characteristics of the freshwater stingray Potamotrygon wallacei in response to seasonal variations in the Middle River Negro, analyzing the effects of these changes on its hematological and biochemical parameters and investigating the relationship between these changes and the physicochemical composition of the water. The animals were captured in lakes and marshes in the Mariuá Archipelago in River Negro. Five field collections were carried out during periods of different flood pulses. Blood was collected by puncture of the gill vessel after the animals were anesthetized. Hematological parameters were determined by routine methods for stingrays. Blood parameters reveal close relationships with changes in river levels, which occur throughout a hydrological cycle in the Middle River Negro region. Therefore, this indicates that the hematology of P. wallacei can be used in monitoring, indicating modifications of adverse environmental changes; however, this ecophysiological association is a complex process and needs to be further investigated.

The increasing demand for sustainable and cost-effective feed alternatives has stimulated the use of agro-industrial by-products in poultry nutrition. This study evaluated the effects of acid silage from pirarucu (Arapaima gigas) by-products (ASP), derived from fish-processing waste, on growth performance, physiological responses, and meat quality of slow-growing broilers. A total of 240 male Label Rouge broilers were assigned to diets containing 0, 1, 2, or 3% ASP from 8 to 56 days of age. Moderate ASP inclusion levels (1–2%) improved (p ≤ 0.05) growth performance by increasing weight gain and improving feed conversion ratio, particularly during the grower and finisher stages. Hematological analyses demonstrated favorable physiological responses, including increased (p ≤ 0.05) hemoglobin concentration, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin. Plasma biochemical parameters indicated improved (p ≤ 0.05) protein metabolism, with higher total protein, albumin, and globulin concentrations, while glucose, cholesterol, and urea remained unaffected (p > 0.05). Carcass evaluation revealed improved (p ≤ 0.05) breast yield at 2% ASP inclusion, and breast composition showed increased (p ≤ 0.05) protein, lipid, and mineral deposition, accompanied by reduced (p ≤ 0.05) moisture content. However, the highest inclusion level (3%) did not promote additional productive benefits. These findings demonstrate that moderate ASP inclusion (1–2%) can improve productive efficiency and meat nutritional quality while promoting sustainable reuse of aquaculture by-products, supporting circular and environmentally responsible poultry production systems.

Determining hematological values is essential to provide baseline health and condition data. We evaluated the hematological parameters of free-living individuals of Caiman crocodilus and Melanosuchus niger from the middle Negro River region of Brazil. We captured 18 C. crocodilus and 16 M. niger. Blood was drawn using syringes containing 10% EDTA, and blood parameters were determined as previously described. The analyzed erythrocyte parameters were similar across the species, demonstrating that, despite their different sizes, they share similar strategies for oxygen absorption and transport in the blood. In the morphological analysis of blood cells, erythrocytes, erythroblasts, thrombocytes, lymphocytes, neutrophils, azurophils, heterophils, and basophils were found, and, in the quantification of leukocytes and thrombocytes, it was noted that lymphocytes are the central cells in the blood of the Amazonian caiman. In the plasma metabolite results, no significant differences were observed between glucose and total protein levels. Key physiological parameters were established to assess the health of C. crocodilus and M. niger, enabling the application of this information to sustainable captive production programs and helping to reduce pressure on wild populations.