Effects of cyanotoxins produced by Raphidiopsis raciborskii T3 strain and temperature on the reproductive axis of Neotropical catfish

Human activities are causing environmental degradation such as air and water pollution. These processes can increase cyanobacterial blooms, which are capable of producing cyanotoxins and have become a problem in public water supply reservoirs. Thus, the aim of this study was to evaluate the possible endocrine disrupting effects of increased water temperature and cyanobacteria in fish. For this, the crude extract of Raphidiopsis raciborskii (formerly called Cylindrospermopsis raciborskii), a neurotoxin-producer, was produced. Male and female Rhamdia quelen fish were exposed to different treatments: control at 25°C, control at 30°C, extract equivalent to 100,000 cells of R. raciborskii.mL-1 at 25°C and extract 100,000 cells of R. raciborskii.mL-1 at 30°C. After 96 h, the fish were anesthetized and blood collected and centrifuged to obtain plasma for hormone analysis. After being weighed and euthanasia, the liver was sampled for vitellogenin gene expression and the gonad for sexing. The data were analyzed in order to evaluate the effects of the isolated increase in temperature and the effect of exposure to the cyanobacterial extract under two different temperature conditions, separately between genders. Temperature alone was able to increase the expression of vitellogenin in the liver of females. Aiming at a current scenario, exposure to cyanobacteria extract at 25°C proved to be anti-androgenic in females, including increased vitellogenin gene expression and reduced testosterone levels. In the scenario of exposure to water at 30°C, fewer alterations were found, but a reduction in vitellogenin expression was observed for both sexes. These results indicate that the increase in water temperature alone can cause changes in reproductive levels, as well as exposure to saxitoxins present in cyanobacterial extracts, the latter being mainly due to the current temperature conditions. Thus, the warming and the cyanobacteria present in the water can lead, in a long-term, to population changes in Rhamdia quelen.