Aquaculture is fertile ground for sterile stocks

The Centre for Aquaculture Technologies (CAT), a leader in genome editing, has successfully applied this technology to various aquatic species, improving key traits such as growth rates and feed conversion, according to a report by 

The case for sterility

There are strong arguments for breeding animals that don’t undergo sexual maturation, as this aligns with key goals of the aquaculture industry. Sexual maturation can cause undesirable behavioral changes, such as increased aggression, which can lead to welfare issues and higher mortality rates.

Dr Debbie Plouffe, vice-president of business development at CAT highlights that not focusing energy on sexual maturation boosts growth rates and improves Feed Conversion Ratio (FCR), which is commercially beneficial, as it reduces feed costs while maintaining fish production. This also supports sustainability and business interests. Additionally, diverting energy from sexual maturation improves fish welfare by strengthening their immune system, making them less prone to disease, with environmental benefits as well.

Plouffe notes the concern of growing cultured animals near wild ones, as traits beneficial for aquaculture might be transferred to wild fish, which could affect their success. However, switching to sterile stocks offers advantages by improving production efficiency and reducing the environmental impact of the aquaculture industry, which plays a key role in feeding the planet.

Dr. Xavier Lauth, CAT’s director of innovation, emphasizes the need for environmentally responsible aquaculture to address food security as the global population approaches 9 billion. He stresses that immediate solutions are necessary to ensure sustainable food production. Plouffe further explains that starting with sterility in aquaculture can eliminate environmental concerns and simplify regulations, creating alignment between producers and consumers for sustainable production, improved animal welfare, and the potential for additional genetic traits like disease resistance and nutritional enhancements.

Sterilisation techniques

Triploidization is a common method for inducing sterility in farmed aquatic species, such as Pacific oysters and Atlantic salmon. It involves applying hydrostatic pressure to fertilized eggs, creating fish with three sets of chromosomes. However, this method has limitations, including lower survival rates during early development and increased skeletal deformities. Additionally, triploidy is not 100% effective at ensuring sterility, and it can be impractical for farms that rely on natural breeding. This makes it a risky option, especially when genome-edited animals are involved.

Lauth emphasizes that when dealing with genetically engineered (GE) fish, there must be 100% efficacy to ensure that no fish can escape and breed with the wild population, preventing genetic mixing.

The production of sterile fish has been a key research focus for decades, with methods beyond triploidy, such as hormone treatments, heat shock, small molecules, or morpholinos. However, these approaches have not been widely adopted due to high costs, integration challenges, or negative effects on fish health. A reliable sterilization strategy is essential for farming genetically engineered fish, which current non-genetic solutions cannot ensure, according to Lauth.

The advantages of GE

The CAT team believes genome editing is the most effective method for inducing sterility in fish, offering both efficiency and efficacy. They’ve developed strategies to create broodstock that produce entirely sterile progeny using genome editing. The goal is to have animals that function normally in hatcheries, with sterility achieved naturally without additional intervention. To produce genetically sterile and monosex fish, CAT uses two approaches: one involves a surrogate parent, and the other, still in research, focuses on manipulating germ cell formation to produce sterile offspring. These methods have been successfully propagated for at least four generations.

The CAT team has been developing gene editing techniques to create sterile fish with improved growth and performance. By targeting specific genes, they’ve created healthy, sterile fish that allocate energy to somatic growth rather than sexual maturation. This has led to a 30% increase in growth rates and a 10% improvement in feed conversion efficiency in edited tilapia. The team has also commercialized a product called Sterility+, which combines sterility with other beneficial traits for farming. Their results show significant improvements compared to traditional breeding programs.

Challenges

CAT is focused on making various aquatic species sterile, achieving a 100% success rate with finfish so far. Their main target is Atlantic salmon, where sterilization could prevent early maturation, saving the sector around half a billion dollars annually. They also aim to work with commonly farmed species like tilapia, which they have been researching for over 10 years. CAT is exploring marine pelagic fish and crustaceans, particularly vannamei shrimp, and has made breakthroughs in developing tools for commercial-scale operations, such as delivering editing enzymes to shrimp embryos.

Despite the potential of genome editing for creating sterile fish, several challenges remain before they can become commercially viable. Key obstacles include regulatory hurdles, though the success of genome-edited red sea bream in Japan brings optimism. Cost is another issue, but proponents argue the technology offers significant returns on investment. Social acceptance also poses a challenge, but experts believe increasing awareness and support from producers can help. Drawing parallels to the acceptance of in vitro fertilization, they believe public perception can change over time as benefits become more recognized.

VFM