Zebrafish Research Paper

The pesticide had an adverse effect on the hatching success of eggs and survival rate of the embryo. The pesticide was assessed for its toxic potential and it was hypothesized that in the exposure water it will be harmful to the development of zebrafish embryos and our findings prove that a very low concentration in the water in the laboratory condition does have an impact on the development of the fish embryo. In the embryonic stage, the dead embryos significantly increased in response to the pesticide concentrations 0.0000134, 0.000134, 0.00134, 0.0134, 0.134, 1.34 and 13.4 µg/L and chorion of the egg provides no protection to the developing embryo (Kafeel Ahmad et al 2011). Early life stage is critical for the development of tissues and bones, and exposure to toxic
pesticides can disrupt the process of development.
The result from the present study gives an idea of the type of effect the pesticide has on the embryo of zebrafish. Though the neurotoxicity of chlorpyrifos and cypermethrin has been much studied in rodents, little is known about the teratogenicity and developmental toxicity to fish in early life stages. In nature, fish are not exposed to single chemicals, but to a mixture of pollutants in aquatic system. The behavior of chemical mixtures in aquatic species is based on their toxic mode of action. Fish species possess specific characteristics for their use in environmental hazard and risk assessment (Jinyoung Lee and Jennifer, 2014). Significant differences in the spawning success have been reported after exposure to pesticides and effect on early life stages in zebra fish (Sisman, 2010). Fish embryo toxicity test is a non-animal test developed as an alternative for fish acute test, in Germany for the whole effluent toxicity testing of wastewater treatment by Adam et al (2011). Zebrafish and its
early life stages were reported to be sensitive to low levels of Alphamethrin in aquatic environment (Ansari et al 2012). Delay in hatching at higher concentration of chlorpyrifos has been reported indicating that chlorpyrifos could be inhibiting the release of chorionase and due to osmotic disturbances interfering with hatching enzyme activity. During hatching process, the chorion is digested by the enzyme chorionase from the gland cells of the embryo. The enzyme gets accumulated in the perivitelline space and induces its breakdown of chorion to release the larva (Basireddy et al 2013) In the present study the surviving embryos exhibited a delay in the hatching process at 0.134 µg/L. The toxic effect of the pesticide was increased with increase in concentration of pesticides and exposure time to embryos. In this experiment similar observation of increase of toxicity was observed in the embryos exposed to different concentrations of the combination pesticide of chlorpyrifos and cypermethrin. Exposure of zebrafish embryos to Pyrethroid caused pericardial edema, type II Pyrethroid being the most potent demonstrating it mildly teratogenic. In low dose body axis curvature, spasms were observed with Pyrethroid toxicity (Demico et al 2010). Phenotype curvature was reported at low concentration of 25 μg/L of cypermethrin to embryo-larval stages of Zebrafish (Shi et al 2010). Trichlorfon an organophosphate pesticide is reported for teratogenicity such as anomalies in absorption of the yolk sac, spine bending, and pericardial oedema in zebrafish embryos (Coelhoa et al 2010). Similar observation of spine curvature was observed in this experiment at very low concentrations of 0.0134 and 0.134 µg/L concentrations, respectively. Interestingly, body curvature observed in zebrafish exposed to pyrethroid was explained as an indication of neurotoxicity not as a result of morphological alteration (Jinyoung Lee and Jennifer, 2014). The Fish Embryo Toxicity test is scientifically supportable as a rational animal alternative model for ecotoxicological testing of acute toxicity of chemicals to fish (Belanger et al 2013). Possibilities of replacing, refining or reducing acute fish toxicity tests in the regulatory framework have been discussed for many years and have been integrated into testing strategies (Busquet et al 2014). It should be considered that development is a complex biological process and the results clearly demonstrate that zebrafish embryos are suitable for screening developmental toxicity and teratogenicity of pesticides.