Farming reproductively sterile fish is the most proficient genetic containment strategy to prevent domesticated escapees from propagating or interbreeding with wild stocks. Sterility carries ecological significance along with economic benefits. Sterilization impedes energy input toward gonadal development, enhancing muscle growth (flesh/fillet yield ) and promoting overall performance and health. Sexual maturation is accompanied by deterioration of flesh quality and suppresses the immune system, which increases susceptibility to stress and disease, causing significant economic consequences for aquaculture. Additionally, sterility is a practical means for producers to protect their selectively-bred IP strains from unauthorized propagation.
Aquaculture is becoming increasingly crucial to resolve the current and projected shortfalls in aquatic food production. Thus, an effective environmentally-friendly containment strategy for large-scale commercial aquaculture operations is desperately needed to achieve the environmental sustainability of this industry . We developed a bath-immersion method to produce sterile fish by irreversibly disrupting primordial germ cell (PGC) migration and development. We demonstrated that the Vivo molecular transporter effectively carries the transient gene silencing Morpholino oligomer (MO) across the chorion, entering the embryo and reaching the target PGCs. Indeed, immersion of salmonid eggs in the Vivo-conjugated MO targeting deadend (dnd), an essential gene in PGC development, effectively disrupted germ cell development and resulted in reproductively sterile fish with minimal gonads that are deprived of germ cells. This technology was successfully applied to salmonid species without introducing any genome modification. Using Dnd-MO-Vivo, 84% and 75% sterility induction was achieved in rainbow trout and Atlantic salmon, respectively. As a substitute for Vivo, we developed a ZP9 molecular transporter that enables the fluorescence labeling of the MO conjugate to advance the immersion technology. Using fluorescence screening, our ongoing experiments focus on optimizing bath immersion and developing a strategy to selectively sort eggs that have sufficient uptake of Dnd-MO to induce sterility (Fig 1).