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Development of sterile fish using an immunization approach

Aquaculture have become an important industry in Norway, and in 2010 more than 1 million tons of farmed salmon and trout were produced. However, Norway has, through international agreements, a special obligation to preserve wild Atlantic salmon populations. There is consensus among researchers that excessive crossing with escaped farmed salmon could be detrimental to the wild salmon populations. Although the number of salmon escaping from Norwegian farms have declined significantly in recent years, the number of fish per production unit have increased as the net pens used today are bigger. Potentially, a large number of fish may  escape from even a single incident. If the goal is to ensure that fish farming do result in permanent change in the genetic characteristics of wild salmon, salmon farming should be based on the production of sterile fish.

The possibility of producing sterile triploid salmon has been explored in recent projects. This technology is already in use in rainbow trout farming in Europe, as well as in salmon farming in Tasmania. However, triploid salmon is more susceptible to the development of bone deformities, and more sensitive to adverse environmental factors like low oxygen levels at high sea water temperatures. In addition, triploid males develop secondary sex characteristics and migration behavior, and may disrupt spawning of the wild salmon if present in a river, even if they can not produce viable offspring. It is necessary to develop alternative and improved technology for producing sterile salmon. The International Cooperation to Sequence the Atlantic Salmon Genome (ICSASG) will provide more information about genes regulating sex differentiation and gonadal development in the embryo, as well as controlling sexual maturation in larger fish. This opens for novel approaches to the development of alternative and more specific methods for producing sterile fish. Accordingly, an application was sent to and granted by the Research Council of Norway’s Biotechnology program, BIOTEK2021. In this project we will use information from the salmon genome in order to develop vaccines that can make farmed salmon sterile, and thereby unable to interact genetically with wild salmon populations. The project is called:

"SALMOSTERILE: Sterile salmon by targeting factors involved in germ cell survival: novel vaccination strategies for sustainable fish farming."

Will stop gametes from developing

In this project we attempt to make vaccines directed against proteins controlling the survival of early germ cells (primordial germ cells, PGCs) or gametes just before puberty. Experiments with zebrafish have shown that germ cells requires survival signals, and at the disappearance of these signals, the cells are arrested in development and undergo programmed cell death (apoptosis). The main concept behind the brood fish vaccination approach is that a sterility vaccine in will inactivate sex cell survival proteins in the developing salmon larva, and thereby forcing the PGCs into apoptosis. The gonads of the developing fish will be devoid of gametes, and unable to produce eggs or sperm the fish will be sterile. Such a vaccine may be given to the mother prior to egg maturation and spawning, as maternal antibodies will be transferred to the egg. Such a technology will be very cost-efficient, as vaccination of one female lead to sterility in more than 15 000 offspring.

An alternative approach is to vaccinate the fish individually at the pre-pubertal stage by targeting immature germ cells. Such a vaccine will be designed to attack proteins specific for germ cell-supporting cells in the gonads, which are essential to the survival of the germ cells. This type of vaccine may be given within the regular vaccination scheme for salmon smolts.

Lessons from Zebrafish

For both alternatives the choice of target antigens is not straightforward, and considerations regarding endogen expression, antibody response and effectiveness must be addressed.  In addition, an efficient transfer of antibodies from mother to egg/embryo is mandatory in order to succeed. The project therefor includes many elements of fundamental research, as well as a more targeted product development to promote implementations of results.  The more formative parts involve searching for vaccine candidates using deep sequencing technology of different gonadal developmental stages from both salmon and zebrafish.  Resources like the draft Atlantic salmon genome and zebrafish databases will be actively used in order to screen for vaccine candidates, and knock-down effects of candidate genes will be tested in studies of both salmon and zebrafish. Studies in zebrafish and Medaka have demonstrated that fish without PGCs develop into sterile males, whereas loach lacking germ cells will develop into sterile males and females. It is still not clear whether a sterile PGC deficient salmon will be mono-sex or mixed sex, this information is very important to establish. This will be done either by using knock-down by synthetic nucleotides or by knocking out genes using genetic modification (for research purpose only).

The ethical and social aspects of the project will be elucidated through a so-called ELSA (ethical, legal and societal considerations) component.

The project is financed by the Research Council of Norway’s BIOTEK2021 program, and is a collaboration between different research groups in Norway, including IMR (Project management), NOFIMA and the Universities of Tromsø and Bergen. The collaboration also includes the University of Utrecht and the Max Planck Institute as well as four industrial partners; AquaGen, Lerøy Seafood, Vaxxinova and MSD Animal Health Innovation. The project commenced in January 2013 and will run for four years.

Contact

Anna Wargelius
+47 55 23 63 45
+47 90 84 81 68