Teratology in zebrafishembryos : a tool for riskassessment

Abstract: Teratology, study of abnormal prenatal development, as a descriptive science has starts with written language. The modern experimental teratology era started in the early quarter of 20th centaury. Since the thalidomide catastrophe in early 1960s regulatory agencies launched requirements for new drugs to be thoroughly tested on animals priorto human use. One of the major concerns in the teratological studies is the mechanism of teratogenesis; it is very difficult to know the exact mechanism of teratogenesis. However there are many proposedmechanism of teratogenesis by Wilson 1973. Teratogens induce one or multiple unique pathogenic responses in the developing embryos. Susceptibility f teratogenesis varies with age and therefore can be divided into three developmental periods: early embryonicdevelopment, organogenesis and early differentiation, and late embryonic development. Animal based studies provide the initial guideline if a chemical or drug may present a teratogenic risk. A variety of laboratory animalsfrom different classes of animals are being used for the teratological studies. Rat, rabbit, mice, hamster, and non human primates are the most prevalent laboratory animal species of the mammal class. Xenopus laevis of the amphibian class has been used and suggested asa model for mammalian teratogenicity. From the bird class chicken, duck and quail have been used most often in laboratory studies. Zebrafish, Japanese medaka and fathead minnow are the most commonly used laboratory fish species, promoted by OECD for future testing of chemical toxicity. Teratogens can be classified as recreational and social teratogens, pharmaceutical teratogens, industrial and environmental teratogens, agricultural teratogens, andmetabolic and infectious diseases. In the present study model substances were selected from the different classes of teratogens. The selected substances were; retinoic acid, lithium, ethanol, 6-aminonicotinamide, ochratoxin A and arsenic,