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N&H TOPLINE: Vision charted for 21st-century U.S. aquacultureN&H TOPLINE: Vision charted for 21st-century U.S. aquaculture

Multi-trophic aquaculture involves re-tasking production byproducts like nitrogen waste from fed aquatic species to fertilize plants or to feed aquatic plants.

Tim Lundeen 1

November 9, 2018

7 Min Read
N&H TOPLINE: Vision charted for 21st-century U.S. aquaculture
Auburn University associate professor Jesse Chappell feeds fish that are part of an aquaponics project, a process which takes nutrients from fish waste and uses it to grow vegetables.Auburn University

Auburn University’s Aquaponics Working Group has a new vision for U.S. aquaculture, one that includes far more predictability and efficiency than today’s timeworn models of commercial fish production, the university said in a story that originally appeared in the Auburn College of Agriculture’s alumni magazine The Season.

“Need is the mother of invention, and that’s what is driving much of this research,” said Jesse Chappell, a member of the group and associate professor and Alabama Extension specialist in the College of Agriculture’s School of Fisheries, Aquaculture & Aquatic Sciences.

“We’ve put together a multidisciplinary team from across campus to cover every aspect of a multi-trophic system of aquaculture production,” Chappell said.

In addition to Chappell, members of the team include School of Fisheries, Aquaculture & Aquatic Sciences professor Terry Hanson, department of poultry science professor Tung-shi Huang, department of horticulture assistant professor Daniel Wells, department of biosystems engineering assistant professor David Blersch and director of campus dining Glenn Loughridge.

Multi-trophic aquaculture is the process of re-tasking production byproducts such as nitrogen waste (nitrate) from a fed aquatic species (catfish or tilapia) to fertilize plants or to feed another aquatic (plant) species, the group said. Fish waste naturally produces high concentrations of nitrogen that can be used to fertilize a variety of plants.

This approach helps to conserve nutrient resource inputs in feeding fish while still yielding maximum farming returns over a limited acreage, Auburn explained.

“When we make an investment in feed nutrients, we can pass it through farm animals and add value to it,” Chappell said. “Fish are very efficient animals, but even they keep only about 25% of the feed they take in, turning it into fish biomass. It excretes the remainder of the nutrients in some form or another.

“That nutrient investment has value in whatever form we can capture. If we throw it away, we are literally throwing money away, and then we have to pay an environmental price,” he added.

The U.S. aquaculture industry is in the same place the poultry and swine industries were in more than 60 years ago, Chappell said, so change has been a long time coming.

“In the 1950s, the poultry industry was moving away from pasture production of broilers and into chicken houses like we see today,” he said. “The same goes for swine. People still grow hogs in piney woods, but that’s not where most of them are grown. That’s because of the high level of animal care and efficiencies that are common in controlled systems as compared to open systems.

“Fish are tracking the same paths and for exactly the same economic drivers as these other animal protein production enterprises: gaining the predictability and the high level of survivorship and efficiency that this type of system can give us,” Chappell added.

Methods are available today that allow for the almost full utilization of the nutrient investments made in aquaculture, Chappell noted. “We want to capture those valuable nutrients that we’ve purchased, pass them through the fish and then recapture the nutrients and water as we pass them through a variety of plants to turn it into some kind of marketable form,” he said. “That’s what this advanced system is all about.”

Auburn’s multi-trophic project actually began about 12 years ago with one greenhouse equipped with a fish production system and an adjacent greenhouse equipped for plant production, Chappell said.

“It’s important that the greenhouses be de-coupled — that is, not occupying the same space — because if we have plants in the fish house, they would always be moist, creating an environment for increased disease pressure and incidence of plant losses,” he said.

The two production platforms are hydraulically connected through the water system. “We feed the fish, and they absorb as much of the feed nutrients as possible, transforming our feed investment into fish biomass,” he said. “They will retain and excrete the balance.”

This system is designed in such a way that it’s not producing or exporting manure, Chappell said.

The initial system operated for several years with various demonstration projects conducted by researchers and students, Chappell said.

“In the last two to three years, we’ve been able to link up with the Campus Dining Services,” Chappell said.

The original greenhouses, for both fish and plants, have been refurbished, and two additional greenhouses are being built to produce even more vegetables for student dining facilities.

“We provide 250-350 lb. of live fish per week [tilapia] that are dressed and made available for use in the campus kitchens,” Chappell said. “We produced peppers during the hot summer season, and we’re now growing fall crops and those that tolerate more moderate temperatures.”

Chappell has worked with pond aquaculture for many years, but he believes the multi-trophic system represents a different, better way of doing things.

He envisions a 2,000- to 3,000-acre tract of land with a feed mill as its central hub to provide the feed necessary for an array of fish production barns.

The idea of this type of system is already being discussed in Asia, he said.

“If a feed mill can generate 40,000-50,000 tons, you could easily produce 30 million lb. of tilapia out the back door in thermally controlled barns,” he said. “Right now, there’s not enough tilapia produced and processed in the United States to push back against the avalanche of product coming in from all over the world. Many of our fish businesses are small, family-owned businesses, and it’s very difficult for them to compete with large-scale, integrated businesses located abroad.”

This concept, Chappell said, makes economic sense because so many cost points can be eliminated. Everything can be done on one tract of land to fully capture and re-task the investment made in nutrients, water and energy.

“Using an Auburn-developed technology, we’d take the slaughter plant waste and turn it into fish meal, with no odor nor wastewater,” he said. “It’s a flash-drying technology that turns discarded processing waste into dry meal in about two minutes. We can sell or use that fish meal. It’s currently selling for $1,700-1,800 per ton for the quality meal this technology provides.”

The water recovery element will reprocess the water from fish systems, taking the manure out of the water and digesting it to form methane or biogas to provide energy to help operate the machinery in the feed mill or processing plant -- “or we can make heat with it. There are a variety of things you can do with biogas,” Chappell said. “We can take residue from methane production and put it out as a land application side-dressing on our hybrid poplar or eucalyptus trees. We make biogas from the solids we capture and produce a lot of vegetables, fruits and flowers using nitrate-rich water.”

Current fish production systems are monocultures, and producers spend a lot of money dealing with the waste load, Chappell said.

“We can offset the cost completely and often earn more on the plant biomass than on the fish,” he said. “In traditional aquaculture, we fill ponds, but we don’t pass water through ponds. We need a fair amount of water to operate our ponds, but the controlled environment system we envision reduces water use by more than half. This approach reduces our water budget and our carbon footprint because we don’t have trucks running up and down the road as typical in traditional systems. Each aspect feeds the other using this approach.”

In the end, Chappell said, it’s all about good business.

A good pond manager with catfish or tilapia in Alabama might produce 10,000 lb. of fish per acre, but a very crude multi-trophic system routinely produces 350,000 to more than 1 million lb. of live fish per acre, depending on the type of system used, Chappell said.

Auburn’s aquaponics research has attracted more than $1 million in competitive grants thus far, according to aquacultural economist Hanson.

“Producers ultimately want to know if they can make money,” Hanson said. “They need to know if they can get a return on their investment and make a profit, and that’s part of the work we’re doing.”

The vision of Hanson and other researchers is that U.S. consumers will eat more fish when it comes from commercialized aquaponics technology.

“At its height, the U.S. consumption of fish reached 16.5 lb. per person per year, and that’s much lower than the remainder of the developed world, where per-capita consumption is at least 30 lb.,” Hanson said. “I hope people will eat more when the fish come from an aquaponics system, where consumers can get their protein and vegetables all from one source.”

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