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Vliv syntetického progestinu etonogestrelu na sekundární pohlavní znaky a histologii gonád živorodky Wingeovy (Poecilia wingei)
PECH, Michal
Synthetic progestins are steroid hormones, which are not only part of the hormonal contraceptives, but they are also used to treat a number of health problems in human. Due to the widespread use of progestin-based drugs, their residues are being found in wastewaters, from where they also enter into the wastewater treatment plants and surface waters. The aim of this thesis was to assess whether the synthetic progestin etonogestrel affects the secondary sexual characteristics and gonad histology of Endler´s guppy (Poecilia wingei). During the experiment, males and females were separately exposed to 3.2 and 320 ng.l-1 etonogestrel for 34 days. A group of fish reared in pure water (K) and group of fish reared in pure water containing the solvent dimethylsulfoxide (KS) served as controls. At the end of the test, all the fish were photographed to capture any color changes. Then the fish were sacrificed and fixed in 10 % buffered formalin solution for morphometric and histological analysis. Fish samples taken for morphometric analysis were photographed using QuickPHOTO MICRO 2.3 software and individual morphometric parameters were measured on the images taken. Fish sample processing for histological analysis included decalcification, dehydration, and pouring of the samples into paraffin blocks. Then paraffin blocks were cut with the thickness of about 4.5 um, resulting slides were stained with hematoxylin and eosin. Histological changes of the gonads were determined on the histological samples prepared in this way. In females exposed to both concentrations of etonogestrel occurrence of color spots was observed. Color spots are characteristic for male and in females indicate masculinization. In addition, females exposed to 320 ng.l-1 etonogestrel showed a change in anal fin morphometry to a gonopodium-like structure (modified anal fin of males serving as helping copulatory organ), a sign also suggesting masculinization. Furthermore, exposure of etonogestrel in both lower and higher concentration of etonogestrel reduced number of mature oocytes in the ovaries, and their occurrence decreased with increasing concentration. In males exposed to both concentrations of etonogestrel a smaller ratio of the length of 4th ray to the length of 6th ray of gonopodium was found. In addition, at concentration of etonogestrel 320 ng.l-1 a greater ratio of the length of 6th ray to body length and extension of length of 6th ray was observed. Although there were no changes, which would indicate hypermasculinization, these changes could have a negative impact on reproduction, or sexual selection by the female. Etonogestrel exposure had no effect on the normal development of testes, because predominantly mature spermatophores were found in males of all treatment groups. Based on these findings, we can say that etonogestrel, like other progestins, represents a real risk to fish if it occures in aquatic environment at concentrations reaching units of ng.l-1.
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