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ARS Home » Northeast Area » Leetown, West Virginia » Cool and Cold Water Aquaculture Research » Research » Research Project #434347

Research Project: Production of Reproductively Sterile Rainbow Trout for Environmentally-Responsible and Economically-Sustainable U.S. Aquaculture Industry

Location: Cool and Cold Water Aquaculture Research

Project Number: 8082-31000-012-11-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Oct 1, 2017
End Date: Aug 31, 2019

Objective:
Induction of sterility is critical in rainbow trout (Oncorhynchus mykiss) aquaculture to improve production efficiency and for genetic containment. Growth and fillet quality traits are adversely affected in salmonids by sexual maturation which in most strains of rainbow trout is at two years of age in females and can be earlier in males. Even without the need to maintain flesh quality or improve growth efficiency, sterilization is a valuable tool used in aquaculture to induce sterility for genetic containment for either environmental protection purposes or to protect the intellectual property resulting from selective breeding efforts. Triploid induction strategies are most commonly used for sterility induction in salmonids. Unfortunately triploid fish have been shown to exhibit inferior production traits including growth before sexual maturation and overall survival, particularly under sub-optimal culture conditions. Furthermore, although the females fail to grow ovaries, triploid males still undergo maturation with testes comprising up to 20% of body weight. An alternative method for induction of sterilization is clearly needed. A fish sterilization technology that utilizes a molecular transporter (called Vivo) that can effectively carry a Morpholino oligomer (MO) against the deadend gene (dnd-MO-Vivo) into fish embryos has been developed. Deadend is an essential gene for fish primordial germ cell (PGC) development. The dnd-MO-Vivo complex successfully disrupted embryonic PGC development and resulted in the production of reproductively sterile fish, without appearing to affect any other physical characteristics of the fish. The technology was developed in the zebrafish and preliminary efforts for adapting the technology to commercial species have been implemented. Refinement of the technology is required to achieve 100% sterility induction and reduce production costs. Evaluation for key production traits such as growth related traits are required to determine the value of the sterilized animal as a cultivar. The availability of this technology will increase production efficiency and promote the development of environmentally friendly next-generation US and global rainbow trout aquaculture industries. Three specific aims were developed to 1) optimize the dnd-MO-Vivo/dnd-MO immersion protocol to determine the most economical condition that achieves 100% sterility induction in large-scale commercial production; 2) establish alternative molecular transporter (ZP9) immersion protocols that may further reduce production costs, and optimize treatment conditions to achieve 100% sterility induction; and 3) characterize the growth related performance of sterilized, 3N and non-sterilized rainbow trout from through 18 months of age.

Approach:
Modified methods for inducing sterility in rainbow trout by disrupting germ cell development during early embryonic development will be evaluated. Since the mechanism of PGC development is highly conserved and the essential role of Dnd has been demonstrated in multiple fish species, it is likely that this same strategy to block PGC development by knocking down Dnd will be effective in other farmed fish. The identification of the novel function of the molecular transporter, Vivo, enables the immersion treatment to be used to administer dnd-MO into fish embryos. The molecular transporter is able to effectively transport the dnd-MO conjugated to it through the chorion, enter the egg or embryo, and reach PGCs. Eggs and embryos will be immersed during well-defined developmental stages and time periods, with species-specific dnd-MO-Vivo that is capable of irreversibly disrupting PGC formation, thereby resulting in reproductively sterile fish. Although preliminary data indicated a successful result of applying this sterilization process to rainbow trout, further studies are needed to optimize each parameter that affects the efficiency of compound delivery, in order to achieve a cost-effective protocol for a large-scale commercial application. Concentrations of dnd-MO/dnd-MO-Vivo and incubation times will be varied to identify the minimum concentration and the shortest incubation time to achieve 100% sterility. Other parameters such as incubation temperature that may be of benefit to compound delivery or the action of dnd-MO will also be investigated. As a first step in evaluating the sterilized rainbow trout as cultivar, growth and fillet yield will be compared among 10 families of rainbow trout produced as sterilized fish, normal fertile fish, and triploid fish, through 18 months of age. Specific Aim 1) Optimize the dnd-MO-Vivo/dnd-MO immersion protocol to determine the most economical condition that achieves 100% sterility induction in large-scale commercial production; Specific Aim 2) Establish ZP9 molecular transporter immersion protocols that may further reduce production costs, and optimize treatment conditions to achieve 100% sterility induction. Specific Aim 3) Compare growth (body weight, fork length, condition factor, feed conversion rate) through 18 months of age and fillet yield at 14 months of age among 10 families of rainbow trout produced as sterilized fish, normal fertile fish, and triploid fish.