This topic explores the interaction between retinoic acid and thyroid hormone disruption in zebrafish early development. Retinoic acid and thyroid hormone pathways are endocrine signalizations that play a major role during early development. Indeed, Retinoic acid is a well-known morphogen important for several morphological processes. An excess of RA has been shown to have an impact on several body parts such as the craniofacial, tail, heart, and fins among others. Moreover, thyroid hormone is also known to be implicated in morphological processes during early development. Indeed, thyroid hormone disruption has been shown to impact swim bladder inflation and eye morphology among others. Teratogenicity in the context of ecotoxicology is a major concern as it is a well-conserved mechanism across species and a defect during early development can lead to a decrease in survival and thus impact species population. Both thyroid disruption compounds and retinoid activities are present in aquatic environments. This bachelor thesis will focus on assessing morphological endpoints representative of a crosstalk between both pathway disruptions and will help to contribute to establishing an AOP network between retinoic acid and thyroid hormone pathways in early development. The bachelor will get familiar with concepts and methods such as AOP, OECD guidelines, histological staining, assessment of morphological defect, and dose-response curve. The results will contribute to the development of an AOP network in the context of teratogenicity which will help predict potential adverse effects in early fish development.