CANADA - In terms of sustainability, fish feed remains one of the finfish aquaculture industry’s greatest challenges. To alleviate pressure on wild stocks, there is a growing need for aquaculture to reduce – and ideally eliminate – fish meal and fish oil from carnivorous fish feeds.
Innovation requires feed that provides minimal inputs – the essential and limited nutrients required by the fish, whilst maximising production of quality fish fillets. At the 2016 Aquaculture Canada and Coldwater Harvest Conference held in St John’s Newfoundland, Dr Stefanie Colombo, a postdoctoral research fellow based at Ryerson University, explained how her work involving genomics is helping the industry achieve just that.
In the search for alternative feeds, land-based plant ingredients are considered to offer both environmental and economic benefits.
However, they tend not to be high in many of the nutritional requirements of carnivorous finfish, such as the omega-3's eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) which, amongst other things, are essential for brain and heart functioning in vertebrates.
Whilst carnivorous fish can generally create their own EPA and DHA from the omega-3 precursor, the level at which they can do so is fairly limited.
In the natural environment, most of the EPA and DHA come from the fish’s diet – other fish.
Reducing the EPA and DHA from farmed fish diets can impact fish health, as well as reduce some of the human health benefits associated with eating fish.
One plant-based candidate for an alternative carnivorous fish-feed ingredient is camelina, a flowering plant that is in the same family as mustards and cabbages.
Camelina is fairly unique in the terrestrial plant world in that it contains naturally high levels of omega-3, however it does not supply the EPA and DHA found in the natural diet of carnivorous fish – and the traditional fish-based feed used in carnivorous fish aquaculture.
By genetically engineering camelina, Dr Colombo argues, we could produce plant-based oil with omega-3 levels that matches those found in marine-based diets.
Indeed research involving the use of transgenes from marine algae has resulted in camelina plants that produce EPA and DHA at similar levels that is found in fish oil. Using the genetically engineered camelina in salmon feed has been tested - with positive results. Compared to salmon fed on the traditional fish-based feed, genetically engineered camelina-fed salmon show almost identical fatty acid profiles and good growth.
Genetically engineering camelina is not without its challenges. Since EPA and DHA are not found naturally in terrestrial systems, introducing them could have repercussions – including impacting terrestrial insects who may consume the EPH and DHA in the camelina.
Laboratory-tests by Dr Colombo on the impacts of these omega-3s on Cabbage White Butterflies demonstrated that consumption could produce wing deformities and overly heavy adults.
Understanding and resolving such environmental impacts is a key part of Dr Colombo’s ongoing research - and is vital if genetically engineered camelina can be produced commercially.
Not all fish feed improvements being explored by Dr Colombo are related to genetically engineered the feed.
Understanding the “genetic architecture” of omega-3 biosynthesis and metabolism pathways in the fish themselves, as well as understanding how the fish react to plant-based diets, also has a role to play. For example, this knowledge could assist in selective breeding of fish which produce higher levels of EPA and DHA themselves – meaning a reduced dependency on these omega-3s in their diets.