PRODUCTION OF ALL-FEMALE ATLANTIC SALMON WITHOUT USING STEROIDS

In farmed fish, sexual maturation is associated with a substantial decrease in somatic growth due to the diversion of energy into the development of the gonads. It results in deterioration of flesh quality and an increase in susceptibility to stress and disease. Shockingly, much higher (80%) precocious male maturation has been reported in land-based recirculating aquaculture systems (RAS) compared to other farming systems (20-30%). As RAS technology is a viable and sustainable means to expand US Atlantic salmon production, early maturation in RAS-grown salmon can have significant biological and business consequences. Using an all-female population is a promising approach for preventing early maturation in RAS farming as most grilsing has been associated with males. However, due to the increasing concern of 17α-methyltestosterone, the steroid used to indirectly produce all-female population, released into the environment, no permit is issued to US commercial Atlantic salmon egg producers despite the rising demands. US growers will continuously rely on foreign all-female seed suppliers unless alternative approaches to produce an all-female population are developed.This proposed research intends to study and optimize germ-cell-transplantation technology for a commercial application to produce all-female Atlantic salmon without using steroids. To utilize germ-cell-transplantation technology for commercial seed production, enough recipients carrying donor-derived gametes should be obtained repetitively. However, due to unstable transplantation efficiency, research and development are needed to optimize this technology to be cost-effective. The goal of this proposed research will be achieved by three specific objectives: 1) Investigation of candidate factors for improving ovarian germ cell transplantation efficiency in zebrafish and tilapia; 2) Verification and optimization of the improved conditions obtained from Objective 1 in ovarian germ cell xenotransplantation between Atlantic salmon and rainbow trout; 3) Further optimization of germ cell transplantation to produce more successful male rainbow trout recipients for a commercial-scale all-female Atlantic salmon production.By carrying out these three objectives, we expect to improve the ovarian germ cell transplantation technology to double the success rate to 60% or more compared to the current success rates at 15% to 30%. The outcomes of this proposed research can also be applied to a wide variety of aquaculture species to produce monosex populations without using sex steroids.