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Turn shrimp into vegetarians? It could solve aquaculture’s sustainability problem

Novel amino and fatty acid feed additives promise to remove wild fish from the diet of farmed ones

by Alex Scott
July 18, 2016 | A version of this story appeared in Volume 94, Issue 29

A photo of feed pellets in pool with fish.
Credit: Evonik
Chemical firms are looking to replace nutrients from wild fish with factory-produced amino acids.

Half the fish we eat are farmed, and the share is growing. This would seem to be good news for the world’s depleting wild fish stocks. But the dirty secret is that many of those farmed fish are being fed wild fish for dinner.

Almost a quarter of the 85 million metric tons of wild fish caught each year are used as food for cultivated species. That’s a problem, given that the United Nations says at least half of the world’s recognized fish stocks are fully exploited and about one-third are overexploited or depleted.

One way to put the brakes on this unsustainable food system is to remove meal made from wild fish from the diets of farmed fish. Industry has already begun pursuing this strategy by replacing fish meal with proteins from plants such as soy, wheat, and pea and adding a dose of amino acids and fatty acids.

Small start-ups and big chemical companies such as DSM and Evonik Industries are now developing a wider range of the essential amino acids and fatty acids that salmon, shrimp, and other carnivorous aquatic species get from their diets so that wild fish can be completely removed. Increasingly, feed additives that started out for land animals are being adapted and applied in aquaculture. Farmed fish could be about to go vegetarian.

Chemical firms have recorded some notable wins in this area during the past decade. The addition of nutrients such as d,l-methionine, an essential amino acid first introduced for land animals, has enabled wild fish use in farmed salmon feed to be reduced from 40% in 2008 to about 15% today, according to industry estimates.

But fish have different nutritional requirements from land animals. For example, in both finfish and crustaceans, many different amino acids are absorbed in the gut via a single cellular pathway that has limited capacity. Feeding one amino acid in high concentrations can limit the uptake of others.

Aquaculture nutrition is becoming increasingly important in the shrimp industry. Farmers harvest about 7 million metric tons of shrimp annually, and the business is growing quickly.

Some companies are tackling the absorption problem by developing dipeptides—pairs of amino acids linked together by a peptide bond. Dipeptides are absorbed in a different part of the gut of fish and shrimp than amino acids. When dipeptides are combined with other amino acids, total amino acid uptake is optimized.

Evonik recently introduced Aquavi Met-Met, a dipeptide made up of d,l-methionine. All four of the dipeptide isomers have different kinetics and are each taken up by shrimp digestive systems at different rates, further enhancing methionine uptake.

Aquavi Met-Met has a second benefit in that it dissolves slowly in water, unlike standard methionine. Dissolution doesn’t matter in salmon farming because the fish snatch up their feed pellets the moment they are thrown into the water. Shrimp, on the other hand, let theirs sink to the bottom before eating them. On the way down, methionine leaches into water, reducing the nutritional content of the pellet and potentially leading to the release of nutrients into the water, which could lead to issues such as rapid growth of algae.

In March, Evonik opened a 3,000-metric-ton-per-year facility in Antwerp, Belgium, that makes Aquavi Met-Met for shrimp feed. Evonik says it is able to produce the dipeptide at an acceptable cost because it already manufactures methionine. “The barrier to entry if you didn’t already produce methionine like we do would be pretty high,” says Christoph Kobler, an organic chemist who heads sustainable and healthy nutrition for Evonik.

A photo of shrimp farmer holding shrimp in his hands.
Credit: Evonik
Evonik is targeting the fast-growing shrimp farming market with its Aquavi Met-Met methionine dipeptide.

Pound for pound, Aquavi Met-Met has proven to be twice as effective at supporting shrimp growth as traditional methionine in feed, Kobler says. In a recent trial commissioned by Evonik and conducted by the South China Sea Fisheries Research Institute, adding Aquavi Met-Met to shrimp feed at a concentration of 0.09% allowed wild fish content to be cut from 26% to 10% with no adverse effect on shrimp growth.

Fish feed facts

More than 200 amino acids occur in nature, but only about 20 of them are common. Of these amino acids, 10 are essential to fish, meaning fish cannot synthesize them and must obtain them via diet.

The 10 essential amino acids are arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Lysine and methionine are often the first limiting amino acids, meaning shortfalls limit protein synthesis.

Omega-3 fatty acids are also essential for fish.

The firm is now evaluating whether Aquavi Met-Met could be suited to the needs of other aquaculture species. Evonik is working on novel routes to a dipeptide of lysine, the second-most important amino acid to fish and crustaceans after methionine.

Dipeptides for fish feed are also a focus for the Münster, Germany-based start-up Cysal. It has developed biotechnology-based routes to dipeptides of amino acids including lysine and arginine.

In Cysal’s process, bacteria are fed sugar as a carbon and energy source and ammonia as a nitrogen source to produce an intracellular polyamide consisting of dipeptide subunits. The polyamide is extracted and hydrolyzed using an enzyme to release the dipeptides.

“By varying the production conditions—such as adding a different carbon source during fermentation—we can vary the composition of the polymer and therefore that of the resultant dipeptides,” says Martin Krehenbrink, the firm’s chief technology officer.

Cysal has been developing its processes in a 650-L pilot fermentor. “We do not anticipate any major issues upscaling this to commercial volumes,” Krehenbrink says. “A petrochemical route does not exist for our dipeptides or anything equivalent, so we are not in competition with classical chemistry.”

The company is now in discussions with major fish feed manufacturers about licensing its technology. It also plans to develop one commercial dipeptide each year for the next few years. In this way, Cysal hopes to assist the process of replacing wild fish in feed with plant-derived amino acids, proteins, and carbohydrates.

Arguably, however, growing the millions of tons of soy, wheat, pea, and other crops needed to create a vegetarian diet for fish would simply shift a resource problem out of the oceans and onto land.

Calysta, a start-up with headquarters in Menlo Park, Calif., proposes to get around the sea-versus-land conundrum with a bacterial fermentation process for making fish food out of methane. “The process uses a nominal area of land,” says Chief Executive Officer Alan Shaw, a serial entrepreneur and chemical industry veteran who got his start at the British chemical giant Imperial Chemical Industries.

And Calysta’s process doesn’t just generate one amino acid but all 10 of the amino acids and carbohydrates that are essential to fish and other ocean-dwelling species. The only additive required to make Calysta’s product, called FeedKind, a complete meal for fish and crustaceans is omega-3 fatty acids, Shaw says. Carnivorous fish naturally source essential omega-3 fatty acids from prey, which the prey in turn accumulate by consuming algae. Omega-3 oils are necessary in fish for metabolic functions and as a cellular membrane component.

The technology is based on a patented loop reactor developed by Norferm, a biotech company spun off of Norwegian oil and gas firm Statoil. Calysta acquired the technology two years ago.

The final FeedKind product isn’t expressed by bacteria but rather is the whole bacteria themselves. The methane-consuming bacteria have been modified through a process of accelerated evolution to contain all the amino acids fish require. They were first found around 1970 by researchers from the University of Bath in a hot Roman bath in the university’s eponymous English town.

Calysta plans to start up a small plant in Teesside, England, this fall for producing samples of FeedKind. The firm intends to open its first commercial plant in 2018, most likely in the U.S., where methane is cheap. The plant will be built in three phases and have a total capacity of 200,000 metric tons per year, Shaw says.

A petrochemical route does not exist for our dipeptides, so we are not in competition with classical chemistry.
Martin Krehenbrink, chief technology officer, Cysal

Given that the fish feed market is many millions of tons in size, Calysta anticipates market entry to be straightforward. “If we built 10 of these plants in the next decade, probably no one would even notice we are in the market,” Shaw says.

One of Calysta’s investors is the agricultural materials giant Cargill, which acquired 10% of the start-up earlier this year. “Cargill, the world’s largest salmon feed producer, will help us get to the market,” Shaw says.

FeedKind has been approved by the European Union for use in salmon feed. And Shaw already has his eye on the fast-growing Asian shrimp feed market. The firm has no reason to believe that FeedKind won’t be an ideal food for shrimp, Shaw says. He expects to have results from shrimp feeding trials during 2017.

Omega-3 fatty acids are the one nutrient that needs to be added to FeedKind. Today, they are extracted from wild-caught fish such as anchovies. But Shaw suggests that they could in the future be sourced from genetically engineered algae.

Indeed, DSM and Evonik already are working together to develop omega-3-rich feed additives from algae. “DSM has a great toolbox,” including technology developed by Martek, a business DSM acquired in 2011, says Evonik’s Kobler, who heads up the partnership on the Evonik side. Evonik has large-scale fermentation capability. “We are absolutely heading in the right direction with the project,” he says.

BASF, meanwhile, is taking a different tack to omega-3 fatty acids. The German firm is working to modify canola plants to express omega-3 and other fatty acids for fish and other animal nutrition purposes. Although the company recently announced a cut in plant biotechnology R&D, the project was one of a few it vowed to continue.

“Alternative sources for omega-3 could be of interest, because end customers demand certain omega-3 levels in fish products,” says Hanno Slawski, head of R&D at the Danish fish feed producer Aller Aqua. “In order to fulfill this demand, we will need more omega-3.”

But developing a low-cost route to omega-3 may not be straightforward. Omega3Max, a recently completed three-year project funded by the EU to develop new sources of omega-3, failed to come up with a new process. The partners, led by the Technical University of Madrid, were only able to advance scientific knowledge in the area of blending vegetable oils with antioxidants.

Their work did indicate that chemical and feed companies have a host of opportunities to develop fish-free aquaculture foods that enhance the properties of farm-grown fish while diminishing the impact of raising them.

Feed companies indicate they are willing to shift to new sources of nutrients, Aller Aqua’s Slawski says. “In the future, it will matter even less than today where these nutrients come from.” 


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