The high and unpredictable mortality of fish larvae during the first weeks after hatching remains a major challenge for the aquaculture sector. Scientific evidence and experience in hatcheries support the hypothesis that detrimental fish–microbe interactions are contributing to this problem. Among the recommended strategies to prevent these health problems is the induction of larvae immune capacity. Accordingly, the major objective of this project is to evaluate the potential of stimulating the developing embryo’s immune system at the earliest possible point by delivering immunostimulants directly to fish eggs. By using a molecular transporter and a bath immersion protocol instead of microinjection, the administration of the immunostimulant can be scaled up to simultaneously treat multiple eggs in a highly versatile, potentially cost-effective, and suitable for industrial applications. To test our hypothesis, we will use the sea bass, a reference marine model in the field of fish immunology but whose value originates mainly from the aquaculture industry. This project aims for significant advances on the state-of-the-art and to bring pioneering technology closer to commercial reality, supporting healthier fish and more efficient production systems.