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Shrimp Aquaculture: Study questions sustainability of plant-based aquafeed

The global farmed shrimp industry has an estimated production volume around four million metric tons (MT), and has become one of the biggest consumers of fishmeal in the aquaculture sector. This has put pressure on aquafeed manufacturers to find suitable alternative ingredients that do not affect the health or growth rates of the shrimp.

A new study by researchers at the University of Stirling’s Institute of Aquaculture concludes that there is an urgent need for a paradigm shift in the definition of sustainable shrimp feed.

The global farmed shrimp industry has an estimated production volume around four million metric tons (MT), and has become one of the biggest consumers of fishmeal in the aquaculture sector. This has put pressure on aquafeed manufacturers to find suitable alternative ingredients that do not affect the health or growth rates of the shrimp.

However, substituting in plant-based alternatives to fishmeal may not be the panacea that ecological campaigners are counting on, according to the recently published research.

The Sustainability Conundrum of Fishmeal Substitution by Plant Ingredients in Shrimp Feeds,” by Wesley Malcorps, models the effects of decreasing the inclusion of fishmeal in commercial diets.

“As demand for shrimp feed increases, feed manufacturers are shifting towards crop-based ingredients, in a move that is mainly driven by economic incentives. This is evidenced by looking at the relative price of fishmeal compared to common plant ingredients such as soy protein concentrate, cereal, and wheat gluten. Some consider the move to be a sustainable transition, as it reduces the dependency on a finite marine resource,” Malcorps told SeafoodSource. “However, a change in ingredients would shift resource demand from the oceans onto the land and could affect the nutritional value of shrimp.”

His team set out to model incremental fishmeal substitution by plant ingredients in feed for giant tiger prawns (Penaeus monodon) and whiteleg shrimp (Litopenaeus vannamei). The models were used to assess the consequent impact on marine and terrestrial resources such as fish, land, fresh water, nitrogen, and phosphorus.

“The study demonstrated that complete fishmeal substitution by plant ingredients could lead to an increased demand for freshwater of up to 63 percent, of land by up to 81 percent, and of phosphorus by up to 83 percent. These are significant increases, as only 20 to 30 percent of the feed is currently substituted,” Malcorps said.

Such increases are mainly caused by the inclusion of resource-intensive crops and their derived ingredients, including concentrates of soybean meal, rapeseed meal, and pea protein, to meet the nutritional requirements of the shrimp.

“While aquafeed consumes approximately 4 percent of global feed crops and therefore just a small share of available water and land, a move from fishmeal to plant ingredients should not be taken for granted as a sustainable solution, particularly in the shrimp sector,” he said.

Malcorps believes that the additional stress on terrestrial resources inflicted by aquaculture will become more obvious over the next few decades, as the sector continues to grow.

“These resources are already under pressure to meet global demand for food, feed, biofuels, and biobased materials. The concern is that increased competition for land could create social and environmental conflicts, and also affect the resilience of the global food system,” he said.

Marine resources are severely stretched because in the 50 years to 2016, global per capita fish consumption more than doubled, increasing from 9.96 kilograms to 20.3 kilograms. An increase in fish consumption of 0.3 percent per year until 2030 is projected, as a growing middle class, particularly in Asia, drives the demand for high-value seafood.

According to the FAO, 59.9 percent of global fish stocks were fished to sustainable capacity in 2016, and 33.1 percent were being fished at an unsustainable level. Aquaculture has grown faster than any other food producing sector, and in 2016, was responsible for 80 million MT of production (46.8 percent of global fish supply) compared to 90.9 MT of wild-capture fish.

Malcorps and his team hope that their model can be used to kick-start the industry into taking an in-depth look at quantitative data on the consequences of sea-land linkages resulting from the substitution of fishmeal with terrestrial ingredients. He emphasized that the study’s model, which was built to investigate shrimp, can also be applied to farmed freshwater and marine finfish.

The researchers suggest that much greater innovation is needed in shrimp feed, and argue that use of byproducts and novel ingredients such as microbial biomass, insect meal, yeasts, micro/macroalgae, and macrophytes should all be explored further.

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