Centimeter-scale aquatic robots could be used in environmental monitoring, exploration, and intervention in aquatic environments. However, existing robots rely on artificial polymers and commercial electronic components, which can pollute and disrupt sensitive ecological environments if they are not retrieved. To address these challenges, we describe a fully biodegradable and fully edible self-propelled device that leverages the Marangoni effect for autonomous propulsion. The body of the edible aquatic robot is made of freeze-dried fish food and is powered by a water-triggered pneumatic reaction that produces motion by sustained release of a surfactant that is safe for aquatic fauna. The device's biodegradable and non-toxic composition allows for safe environmental deployment for environmental sensing, delivery of nutrition or medication in aquatic environments. The proposed method substantially expands the potential benefits of small-scale aquatic robots that could be deployed on a large scale without the need to retrieve them and even provide nutrition to wildlife at the end of their lifetime as animals do.