The production of high quality juveniles is still a bottleneck in the farming of numerous fish species. Survival until the juvenile stage is typically as low as 10-15% for many species. Early life protection against pathogenically hostile environments is achieved through a mixed passive immunity transmitted from maternal sources to offspring during oogenesis.

However, many of these maternally transferred factors usually persist only for a very limited duration and completely disappear in the late larval stage. Parental experience with parasites and pathogens can lead to increased offspring resistance to infection, through a process known as transgenerational trained immunity. However, the mechanisms underlying transgenerational trained immunity are poorly understood. Among the potential pathways leading to the realization of transgenerational trained immunity it can be suggested: 1) transfer of active immune components; 2) transfer of PAMPs to offspring and 3) epigenetic modifications. Transgenerational trained immunity offers an attractive approach in intensive fish larval rearing. We will use high-throughput omic approaches (genomics and proteomics) to advance our understanding of transgenerational trained immunity in fish. We also propose to explore a new and exciting approach; the delivery of immunostimulants directly to fish eggs by an immersion bath. To test our hypothesis, we will use two model fish species; zebrafish and a marine medaka. The ultimate goal of the LEGATEE project is to shed light on the molecular mechanisms involved in egg immunity inheritance and will constitute a first necessary step for future progresses in the aquaculture sector and the development of patents.