The many advantages of fish-poo fertiliser

River Stone Fish Farm is turning barramundi manure into an organic liquid plant fertiliser, Swift Grow.

Joseph Ayoub wanted to produce the besttasting barramundi in Australia; that was his simple, original aim.

So, the aquaculture genetics engineer built himself a fish farm in Riverstone in outer suburban Sydney, stocked the tanks with the prized eating fish and called his new venture River Stone Fish Farm.

All was in readiness for his foray into the world of piscine cuisine.

Then a funny thing happened.

One day, Ayoub threw some fish poo – waste residue from the tanks – onto his backyard and plants at home. In no time, he noticed those patches of lawn and plant beds were growing lush and green, a bit like the magic beans in Jack and the Giant Beanstalk.

He soon realised there was something in the fish poo that caused this dramatic reaction among the plants; they seemed to love the stuff. After several years of intensive scientific testing and tuning, Ayoub discovered that when his unique plant-based fish food passed through a barramundi’s gut, it ended up producing manure rich in a natural ecosystem of friendly bacteria – which helped revive depleted soil.

Ayoub then ‘‘pivoted’’, and his plans to produce delectable barramundi gave way to something more ambitious: the gamechanging harvesting of fish manure for agriculture. He partnered with IT engineer Emil Isaac, who has managed and promoted the business, and helped transform it from an operation that couldn’t pay its rent in 2018 to one that has a multimillion-dollar turnover in 2023.

The company’s certified organic liquid plant fertiliser, Swift Grow, is sold throughout Australia and exported to the UAE, UK and US.

There are thousands of barramundi in the tanks, and each produces six litres of fertiliser per week, so the poo supply is plentiful.

As Isaac explains, Swift Grow restores soils back to optimal health by restoring its natural microbiome. This has the effect of increasing plant biomass/foliage, photosynthesis and crop yield which, in turn, helps combat climate change: the greener the plant, the more carbon it absorbs.

“The disruptive benefits of Swift Grow are multifaceted,” he says. “It restores the soil’s natural bioactivity, increases water retention and absorbs atmospheric carbon – three times more than untreated soil.”

From a human health perspective, he says, the lost colour, taste and aroma to all food types are restored. Plus bee disease immunity is boosted.

Swift Grow has been scientifically trialled in Dubai on a cucumber crop – yielding 30 per cent more than the next-best fertiliser. It has also been used on nursery plants and golf courses in Australia with similarly impressive results.

The River Stone barramundi have been ‘‘trained’’ to be vegetarian. So, as Isaac says, it’s a perfect closed-loop ecosystem: plants are used to make organic feed pellets, the fish eat the pellets then produce manure which is applied back to the plants, and the cycle repeats itself sustainably.

Harvested from the bottom of the tanks, the poo is treated to remove the pungent smell and extend its shelf life to four years, then bottled.

Swift Grow costs less than half of most chemical fertilisers and requires zero-netenergy to manufacture.

Such has been the success of the product, and Ayoub and Isaac’s role in developing this agricultural phenomenon, the pair have partnered with the University of Western Sydney, where they now supervise sustainable agriculture research at the uni’s AgriTech Hub.