Steroid androgen 17 alpha methyltestosterone used in fish farming induces biochemical alterations in zebrafish adults.

The 17 alpha methyltestosterone (MT) hormone is fed to Oreochromis niloticus larvae in fish farms with the purpose of inducing sex reversal. The aim of this study was to evaluate the toxicity and sub-lethality of MT (99.9% purity) and cMT (a commercial MT with 90% purity) in zebrafish (Danio rerio) adults, where the animals were exposed to concentrations of 0, 4, 23, 139, 833 and 5000 µg/L for 96 hours. Genotoxicity was evaluated by micronucleus test (MN), nuclear abnormalities (NA) and comet assay. A low genotoxic potential of MT was showed, inducing micronucleus, nuclear abnormalities and DNA damage in Danio rerio, depending on the use of MT or cMT, gender and tested concentrations. In the sub-lethality trials, there was a basal difference in the activity of the enzymatic biochemical markers for males and females, while the Glutatione S transferase (GST) activity decreased in all analyzed tissues, and for males the enzymatic activity decreased only in the intestine. Results suggest that MT has a toxic potential to fish because it alters enzymatic metabolic pathways and may pose a risk to the ecosystems.

Steroid androgen 17α-methyltestosterone induces malformations and biochemical alterations in zebrafish embryos.

The synthetic androgen 17α-methyltestosterone is widely used in fish aquaculture for sex reversion of female individuals. Little is known about the amount of MT residues reaching the aquatic environment and further impacts in non-target organisms, including fish early-life stages. Thus, in this work, zebrafish embryos were exposed to two forms of 17α-methyltestosterone: the pure compound (MT) and a formulation commonly used in Brazil (cMT). For MT, a 96h-LC50 of 10.09mg/l was calculated. MT also affected embryo development inducing tail malformations, edemas, abnormal development of the head, and hatching delay. At biochemical level MT inhibited vitellogenin (VTG) and inhibited cholinesterase and lactate dehydrogenase. cMT elicited similar patterns of toxicity as the pure compound (MT). Effects reported in this study suggest a potential environmental risk of MT, especially since the VTG effects occurred at environmental relevant concentrations (0.004mg/l).

Endocrine disruption effects of p,p'-DDE on juvenile zebrafish.

The persistent organic pollutant p,p'-DDE, the major metabolite of the insecticide DDT, has displayed evidence of endocrine disruption through the inhibition of androgen binding to androgen receptors in different species. Although p,p'-DDE was continuously detected in wild fish with abnormal gonad development such as intersex, little is known about its mode of action during gonad development in fish. To elucidate the potential endocrine effects of this pollutant in zebrafish (Danio rerio), juveniles (30 days post hatch) were exposed to p,p'-DDE during the critical window of sexual differentiation. Fish were exposed to sublethal concentrations ranging from 0.01 to 20 µg l(-1) over 14 days and were maintained in control water for an additional 4 months. As core endpoints, the vitellogenin (vtg) concentration was measured at the end of exposure, and sex ratio and the gonadosomatic index were assessed 4 months after the end of exposure. An increase in vtg production in whole body homogenate was observed in fish exposed to 0.2 and 2.0 µg l(-1) p,p'-DDE. No significant differences were displayed in morphological parameters such as the gonadosomatic index of males and females or sex ratio. However, exposed females presented histopathological changes that include the reduction of the number of mature oocytes, which might impair their successful reproduction. These results demonstrate the ability of p,p'-DDE to cause endocrine disruption in zebrafish exposed during gonad differentiation of juvenile specimens. Furthermore, vtg induction by p,p'-DDE in juvenile zebrafish arises as a predictive marker for adverse effects of this DDT metabolite on the ovarian function of female zebrafish.