Humans have been genetically modifying plants and animals for thousands of years with selective breeding.  Since the 1970s, we have been able to modify DNA, creating cisgenic (adding recombinant DNA from the same or similar species) and transgenic (adding recombinant DNA from a another species with which the organism can’t naturally breed with) species.  In the public domain genetically modified organisms for use in the food industry is a highly controversial topic.  On one side, there are concerns surrounding their potential impacts to both human and environmental health.  On the other, there are those who argue that the use of GMOs in aquaculture isn’t just of benefit to the industry, but for food security and even reducing our impacts on the oceans.

In industrialised aquaculture salmon is the leader in terms on net production.  Salmon, like many of the species preferred in western diets, are carnivorous fish.  Feeding them requires fish, which tends to come from wild populations.  Given concerns surrounding global exploitation levels of wild marine species and projected growth in aquaculture, this practice is somewhat unsustainable.  GM may reduce dependency on wild populations for feed and, with forage fish supplies often forming ‘boom and bust’ cycles, alternate feed sources could bring stability for aquaculturalists. 

Created by the biotech company Aqua Bounty Technologies, AquAdvantage® salmon contains a growth hormone from chinook salmon and a promoter from an antifreeze gene found in ocean pout, enabling AquAdvantage® salmon to grow year round, not just seasonally.  Growth time to marketable size is reduced from around three years to just eighteen months, reducing the amount of feed required.  Alternative food sources for carnivorous fish is another option for reducing dependency on wild populations. 

Whilst some aquaculturalists have moved towards a vegetarian diet for their salmon, work by researchers such as Kelly Weaver (University of Miami) suggests that their omega-3 content is severely reduced.  Alternatively, Stirling University’s Mónica Betancor has created genetically modified camelina plants that can produce eicosapentaenoic acid - one of the two omega-3 nutrients that are of benefit to human health – in their seeds.  By adding oil extracted from the plants to fish feed, omega-3 was replenished, whilst feed efficiency, growth rates and fish health remained unaffected. 

As with all forms of intensive farming, disease has been a long running issue in aquaculture, and one that is largely tackled with vaccines and antibiotics.  Their use is not without cost to aquaculturalists, and overuse of antibiotics in particular is an area of public concern.  Research into disease-resistant GM fish may offer a way to reduce antibiotic and vaccination loads.  For example research by Weifeng Mao (Chinese Academy of Sciences) has resulted in a transgenic grass carp with enhanced immunity to Aeromonas hydrophila infection, an opportunistic pathogen that can cause tail/fin rot, ulcers, and haemorrhagic septicaemia. 

Reducing disease-risk is not the only way in which farmed species are being bolstered, with work being done to increase resistance to stress and thermal tolerance, typically with the aim of producing warm water fish that can be farmed in colder waters.

Unfortunately we do not really know what the long-term impacts to wild populations could be, nor to the wider ecosystem, of GM escapees.  A precautionary approach to GMOs in aquaculture is warranted, and indeed possible.  For example, to minimise the risk of interbreeding with wild species, one could ensure GM species are sterile (e.g. triploid).  Indeed, Aqua Bounty Technologies claim their salmon is sterile, and thus the risk of breeding with wild populations is minimal (100% sterility cannot be ensured).  However this approach does not deal with the risk of GM individuals outcompeting their wild counterparts. 

In laboratory experiments conducted at Memorial University Newfoundland, hybrid offspring from GM salmon and wild brown trout (closely related species that are known to interbreed in the wild) were able to outcompete both GM and wild salmon for food, resulting in stunted growth for the salmons.  Whether this could occur to such a scale as to cause problems for wild populations outside a lab is questionable, as is the breeding capacity of hybrids. 

Escapees are well documented, but just what volume of escapism would be sufficient to cause long-term damage is unclear.  Arguably the safest, albeit more costly, solution would be to prevent escapees in the first place by using land-based closed-containment systems. 

Whilst such steps may reduce environmental risk, they do little to allay fears regarding risk to human health - and indeed the health for the farmed animals themselves.  As with environmental risk, there is a lack of research demonstrating risks to human/animal health.  Whether this is because of the paucity of studies in the area or because there really are no risks, is yet to be resolved.  Until such time as these wider issues are addressed, public concern may prove an obstacle for widespread industry implementation.

This story appeared on The Fish Site.