Cadmium is a natural element found in the earth’s crust; it is usually associated with other metals, but due to the impacts caused by human activity, its concentration has increased in the aquatic environment. This metal may damage aquatic animal reproduction, decreasing the rate of fertilization of organisms such as fish. Thus, this study aimed to evaluate the in vitro toxicity of different concentrations of cadmium (0 (control), 0.5, 5, and 10 μg/L) using sperm cells of model organism zebrafish, Danio rerio. Structural parameters, including integrity and fluidity of the plasma membrane, concentration of oxygen species, mitochondrial function and DNA fragmentation were measured by flow cytometry. The following sperm movement parameters were also measured using the computer assisted sperm analysis (CASA) system: motility, time of motility, curvilinear velocity, average path velocity and straight line velocity in μm/s. Significant effects were observed on path speed, straight speed, curvilinear velocity, motility time, progressive and total motility, and plasma and DNA integrity. The results showed that cadmium can negatively affect some reproductive parameters in D. rerio, which may reduce the fertility rate of these animals.

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SummaryThis study aimed to describe the morphology and sperm quality of free-living adult males of cururu stingray Potamotrygon wallacei, endemic from the Rio Negro basin, Brazilian Amazon. The sperm was collected in loco from the seminal vesicle region and fixed in buffered saline formaldehyde solution for further evaluation of morphometry, sperm plasma membrane integrity and sperm concentration. The spermatozoa presented a total length of 138.25 ± 1.82 μm with a helical shape and a long head. A high percentage of cells with intact membrane (98 ± 2%) and normal spermatozoa (92 ± 1%) were observed. The cell concentration was 0.34 ± 0.05 × 1010 spermatozoa/ml of semen. These observations are unprecedented for potamotrygonid species and will serve as a basis for future management and conservation strategies.

The use of animals as bioindicators has been useful, especially in the evaluation of environmental impact of pollutant discharges in aquatic ecosystems. This study, aims to assess the fish Phalloceros caudimaculatus (known as Guaru) as a heavy metal sbioindicator. LC50 (96 h) acute toxicity tests to potassium dichromate salts, cadmium nitrate, lead II nitrate and zinc sulfate, and bioaccumulation of metals such as cadmium, chromium, lead and zinc were conducted. In the bioaccumulation test, for three months standard tanks were used, with different contamination levels above the levels set by local law, a pollution control tank was also set. The following data was obtained in acute toxicity tests LC50 (96 h): Potassium dichromate 164.58 ± 18.75 mg/L, Cadmium nitrate was 29.5 ± 1.21 mg/L, Lead nitrate was 15.5 ± 0.47 mg/L and zinc sulfate was 62.8 ± 2.81 mg/L. The bioconcentration factor (BCF) maintained the order Zn > Pb > Cd > Cr, where the resulting values were considered high for the four elements ranging from 92.4 (Cr) to 1793.1 (Zn). Based on the test results, the Guaru fish proved resistant to the presence of these metals and a showed a high bioaccumulation rate. Thus, it can be used as a bioindicator of heavy metals.