An animal’s ability to effectively capture prey and defend against predators is pivotal to its survival1. A key innovation in many predator-prey interactions is venom, which consists of many toxin proteins that shape its phenotype2. Its unusually direct relationship of gene-toxin-phenotype make it an appealing system for studies at the organismal level 3,4. In this work we use the sea anemone Nematostella vectensis as a model organism as it provides us with the opportunity to test for the first time how toxin-genotypes impact predator-prey interactions. Specifically, we compare a native-population5 and a transgenic line which both have significantly reduced levels of Nv1, the major toxin in adult Nematostella6, to animals with wildtype levels of Nv1. We demonstrate that the transgenic strain phenocopies native anemones lacking Nv1 as they both have impaired ability to defend themselves against grass shrimp, a native predator. Mummichog killifish, unexpectedly are attracted to Nematostella with wildtype-levels of Nv1, highlighting that Nv1 plays a complex role in shaping interspecific-interactions. Finally, we demonstrate an evolutionary tradeoff as the reduction of Nv1 levels causes faster growth and increased reproductive rates compared to Nematostella control lines. Overall, our results experimentally link organism’s venom to its physiology, reproduction and interspecific interactions.