In Booming Aquaculture Industry,
By John H. Tibbetts
Aquaculture production has more than doubled since 2000, putting pressure on the stocks of small fish used to feed farmed salmon and other species. But researchers are now developing plant-based feeds that could put the industry on a more sustainable path.
A Move to Plant-Based Food for Fish
03 Sep 2015
In a quiet valley just outside Bozeman, Montana, a trout stream by the name of Bridger Creek flows past a circle of low-rise buildings, including a structure that holds about 250 tanks of rainbow trout in recirculating water. It is here that a plainspoken scientist is helping to lead a seafood revolution.
For years, Rick Barrows, a fish physiologist with the U.S. Department of Agriculture’s (USDA) Research Service, and other scientists have sought to develop all-vegetarian feeds for farmed carnivorous fish
Plant-based feeds have shown considerable promise in salmon and trout aquaculture.
such as salmon and trout. Their goal has been to reduce reliance on overfished stocks of sardines, anchovies, and other forage fish, but the scientists have faced considerable hurdles.
As recently as the late 1990s, the aquaculture industry was heavily dependent on marine protein, using about three to four pounds of fish — in the forms of fishmeal and fish oil — to grow one pound of salmon. And the biological challenges of using soybeans and other plants to replace the long-chain fatty acids and amino acids found in forage fish have been considerable.
Now, though, Barrows and his team at the Bozeman Fish Technology Center
report that rainbow trout fed a patented all-plant feed, rich in supplemental nutrients, are healthy and grow quickly.
“I was told by many [people] that fish require fishmeal because that’s what they eat in the natural world,” says Barrows. “But that’s just wrong.”
Developing all-vegetarian feeds for fish farming comes at a crucial time for the rapidly expanding aquaculture sector.
Barrows and his scientific collaborators have been on the forefront of creating alternative and all-vegetarian feeds for carnivorous fish farming — a development that comes at a crucial time for the rapidly expanding aquaculture sector. From 2000 to 2012, farmed seafood production doubled from 32.4 million to 66.6 million metric tons
. And aquaculture is expected to play an increasingly important role in providing marine protein
as wild fish stocks decline and the human population soars to an estimated 9 billion by 2050.
At the same time, fishing pressure on sardines, anchovies, menhaden, and other forage fish used in aquaculture feed also has intensified
, in some cases leading to depletion of those stocks. About three-fourths of global supplies of fishmeal and fish oil are produced from these oily and bony small pelagic fish. Tighter fishing quotas and tougher regulation of small pelagic fisheries have pushed up prices of fishmeal and fish oil in recent years.
These developments have led to a push to use ever-greater quantities of plant protein in aquaculture food. In the late 1970s, some scientists began thinking about the possibility of developing an entirely vegetarian feed for carnivorous fish. About a decade ago, scientists began making rapid progress in developing technologies to enhance the nutritional values of plants, particularly soybeans, as replacements for fish in aquaculture feeds. The industry has embraced many of these advances while also continuing to rely on fishmeal and fish oil.
Now Barrows and other scientists have taken another major step, creating the first all-vegetarian feed for nine carnivorous species, and the aquaculture industry has taken notice. The new vegetarian
To create a healthy plant-based feed, researchers have first sought to understand the complex nutrients available in fishmeal and fish oil.
meal formulations and ingredients, however, have not yet been scaled up to commercial production and at this point are costly, says Barrows.
Today the main ingredient in fish feed continues to be soybean meal, and it is chosen primarily for one reason: cost. Peruvian fishmeal can cost more than $2,000 per ton at the high end, while soy-based feeds can cost less than one quarter that amount. Large amounts of fishmeal also are sold to pig, poultry, and cattle producers.
To create a healthy plant-based feed, researchers have first sought to understand the complex nutrients available in fishmeal and fish oil. Over the past decade, scientists tallied 40 ingredients in the fish-based diet, including micronutrients (such as vitamin A, D, riboflavin, and niacin), amino acids (such as
Rainbow trout at the Bozeman Fish Technology Center are fed plant-based foods.
methionine and lysine), minerals (such as iron, zinc, selenium, and iodine), and long-chain fatty acids.
Two crucial omega-3 fatty acids — DHA and EPA — found in fish are associated with human brain health and heart health. Fish derive these fatty acids from marine algae; terrestrial plants do not have them. An algae-based supplement allows the fish’s metabolism to naturally produce DHA and EPA. It is now added to feed pellets that are used by some fish farmers and has helped make plant-based fish food a good alternative to fish-based feed.
“Fishmeal is almost a perfect feed,” says Robert Reigh, director of the Aquaculture Research Station at Louisiana State University. Farmed fish and shrimp can easily digest fishmeal and fish oil, which allow for good growth and survival. “Predatory fish like salmon tend to thrive in an aquaculture environment where they are fed things that they would eat in nature — fats and protein from other fish,” says Reigh. “If you feed them things that they are not attuned to metabolically and physiologically, then you can have problems with poor growth and health problems.”
Scientists, though, have made great strides in meeting those nutritional needs with plants. “If you are going to replace fishmeal with soybeans, then you obviously have to make up those other elements that fishmeal supplies,” says Albert Tacon, an aquaculture nutritionist based in Hawaii.
Thanks to plant-based foods, it is common to use 1 pound of fishmeal to grow 1 pound of fish, a significant decline from the 4 pounds used earlier.
Thanks to the spread of plant-based foods, it is now common to use 1 to 1.5 pounds of fishmeal to grow 1 pound of a fish such as salmon, a significant decline from the 3 to 4 pounds used two decades ago. New research shows that the volume of fish needed in feeds for many carnivorous fish is very low or zero, says Barrows.
At the Bozeman research station, Barrows and his team screen 30 or 50 different feed ingredients a year for rainbow trout, and they ship other feed formulations to labs around the country for nutritional testing on farmed species such as cobia, Atlantic salmon, and Florida pompano. Each species has grown well and quickly on these fishless feeds, though some are not entirely vegetarian.
Barrows has collaborated with other U.S. researchers and with a scientist in Norway who is testing alternative feeds for Atlantic salmon. Barrows and others say that the new feeds are nutritionally identical to fish-based ones. “Once we provide these extra supplements to a feed,” he says, “we’re not turning carnivores into herbivores, we’re turning soybeans and corn into meat.”
One major challenge in formulating plant-based feeds is that each plant develops a mechanism to prevent its seed from being eaten by predators. Soybeans developed chemical means, called “anti-nutrients,” to defend against predators. These anti-nutrients cause an inflammatory condition in some fish called intestinal enteritis, which can slow growth. But researchers have been able to add enzymes
‘With these extra supplements, we’re not turning carnivores into herbivores, we’re turning soybeans and corn into meat,’ says one researcher.
and use other processing methods to eliminate anti-nutrients in plant-based feeds.
This is not to say that farmers are moving entirely away from fishmeal and fish oil. Omnivores and herbivores such as tilapia and carp don’t require fishmeal or fish oil, but many farmers still use them because they are such nutritious and cost-efficient ingredients in the latter stages of production. These farmers often use primarily plant-based feeds until late in production and then use fishmeal and fish oil to “finish” their farmed animals’ growth and nutrition and provide the taste that consumers want.
“When are you looking at the price of ingredients, sometimes fishmeal just makes more sense,” says Jesse Trushenski, a fisheries scientist at Southern Illinois University. “It still delivers the most digestible protein per dollar. But its price is going to continue to climb because of its unique ingredients, growing demand, and limited supply.”
Still, recent advances in aquaculture research have shown that farmed carnivorous fish do not require any fishmeal or fish oil in their feeds. “We have been hit over the head with the notion that farming carnivorous fish means that you have to catch fish in the ocean for its diet, but that’s wrong,” says Michael Rust, science coordinator of the NOAA Fisheries’ Office of Aquaculture.
For 25 years John H. Tibbetts was editor of
Coastal Heritage magazine, covering coastal and marine science and the consequences of climate change. His freelance work has appeared in
Environmental Health Perspectives and other journals.