The untapped potential of marine plants is being investigated by a growing number of researchers around the world – and, among them, the winner of a national award
By Michelle Daw
T he compounds that help seaweed defend itself against viruses, fungi and bacteria could hold the key to a promising natural supplement for farmed aquatic animals to boost their immunity and growth.
This potential is being investigated by Dr Valentin Thépot, winner of the Fishing and Aquaculture Award, a part of the 2022 Science and Innovation Awards for Young People in Agriculture, Fisheries and Forestry, sponsored by FRDC.
Valentin is a researcher at the University of the Sunshine Coast and the aquaculture coordinator for the Anindilyakwa Land Council on Groote Eylandt in the Northern Territory.
The award will allow him to test if the benefits found when feeding fish with a red seaweed supplement can be replicated for farmed Black Tiger Prawns (Penaeus monodon) and novel aquaculture species.
“Aquaculture provides half of the seafood consumed globally, yet disease outbreaks pose a serious threat to the sustainable development of the industry, costing more than $8 billion annually,” he says.
“Australia is free of many diseases that are crippling prawn farms overseas. However, the outbreak of incurable White Spot Disease in Queensland, which led to losses of more than $32 million in 2016–17, showed that we need innovative solutions for disease management and prawn welfare that don’t compromise productivity.”
Valentin says that he saw a 400 per cent increase in immunity (Figure 1) and a 19 per cent boost in growth when the red seaweed (Asparagopsis taxiformis) was included at less than three per cent in pellets fed to Black Rabbitfish (Siganus fuscescens), a tropical herbivorous species and Atlantic Salmon (Salmo salar), a temperate carnivore.
“We also found that this seaweed is stronger than four immunostimulants currently used in aquaculture, including beta-glucan and sodium alginate,” Valentin says.
“This means that a seaweed-based feed additive could one day replace, or at least complement and minimise, the use of veterinary drugs such as antibiotics in aquaculture.”
Valentin says he chose to work on Black Rabbitfish because it is low in the food chain, has tasty white flesh and can produce long-chain unsaturated fatty acids (omega 3s) from short-chain fatty acids. Unlike its carnivorous counterparts, it does not require fish meat and fish oil in its diet.
“This fish also has a wide geographical range in the Indo-West Pacific, as it is found from north of Japan to south of Australia, and it copes with temperatures from 17°C to 31°C,” he says.
“The warming of the oceans due to climate change is already putting pressure on fish farmers growing temperate species with limited thermal ranges. The robustness of Black Rabbitfish in response to some of the effects of climate change is another reason why I wanted to work with this species.”
Valentin found that Atlantic Salmon fed a double dose of Asparagopsis extract supplement had significantly better growth and improved feed efficiency than the Atlantic Salmon fed the control diet.
His new project will evaluate if this feed innovation translates from fish to Tiger Prawns, Australia’s most valuable farmed crustacean. It will also look at whether it can be used in emerging aquaculture species important for traditional owners in northern Australia.
Data from the feeding trial with Tiger Prawns will inform direct-feeding trials on Groote Eylandt with tropical rock lobsters (Panulirus spp.) and sea cucumbers.
Valentin says that winning the award means he can continue working on the project to help establish the potential economic, environmental and social benefits the red seaweed could offer at local, national and global levels.
“The use of novel aquafeed ingredients, such as seaweed, can change the way we treat and prevent disease outbreaks in aquaculture and reduce our reliance on antibiotics,” he says.
“From an environmental and human health point of view, I believe that any effort to reduce our use and reliance on antibiotics in aquaculture is a positive step forward.
“Seaweed dietary supplements can also improve productivity while reducing the environmental impact of the industry. This is especially key in pristine and remote areas such as prawn farms adjacent to the Great Barrier Reef.”
Dr Valentin Thépot and Scott Warramarrba of the Anindilyakwa Land Council check the water quality parameters at the site where they will conduct a tropical rock lobster survey. Photo: Supplied.
Valentin says being able to use farmed seaweed to replace or limit the use of wild-sourced ingredients in aquaculture feeds, such as fish meal and fish oil, will reduce the pressure on wild fish stocks and associated impacts including bycatch.
Another key output of the project will be to estimate the financial benefits from improvements in productivity to ensure broad uptake of seaweed-based feeds in aquaculture. This could include spending less on antibiotics, reduced losses through fish mortality and better profitability through improvements in the feed conversion ratio and growth rates.
Valentin says growing seaweed for feed production can also directly benefit the marine environment as seaweed uses sunlight to take carbon dioxide from the water, which reduces acidification and sequesters carbon in the plant itself.
There is also the potential for aquaculture effluent to be used as fertiliser for the seaweed. This integration of seaweed biofilters would further reduce the impact aquaculture may have on the natural environment. The discovery that Asparagopsis can reduce methane emissions in cattle has sparked the development of seaweed farming in Australia, and Valentin says its potential as a feed supplement for farmed seafood could create another market opportunity for the product.
He says Anindilyakwa Land Council’s vision for the development of aquaculture is driven by the need to secure a sustainable future beyond the closure of the local manganese mine, which is the main contributor to the local economy.
Valentin has been working with the land council on a fly-in, fly-out basis, but he and his family are moving to Groote Eylandt in mid-2022 to allow him to work more closely with traditional owners on the development of sustainable aquaculture enterprises.
He is excited to be working on a project on the frontiers of scientific knowledge with potentially huge social, environmental and economic benefits.
“There are more than 12,000 species of seaweed on the planet, but we only know a handful of the compounds they contain,” he says.
“Seaweeds produce various biologically active compounds as defences against grazers and pathogens, and these can have amazing properties including antivirals, antibiotics and antifungal compounds, which could offer incredible benefits for aquaculture.
“In Australia, we are lagging well behind countries in Asia that grow a lot of seaweed biomass.
“We have thousands of kilometres of amazing coastline, a range of native seaweed species, and growing demand for seaweed for a huge range of products. We need to do more.” f
