The future of vegetarian fish diets

A major criticism of the salmonid aquaculture industry is that despite its ability to reliably provide farmed fish, thereby diverting consumer demand for wild-caught fish, the industry is ironically traditionally heavily dependent on wild-sourced fish meal and oil in its feed production. In addition to environmental concerns, the status of wild fishery stocks, as well as the nature of wild fishing, mean that wild-sourced fish meal and oil prices have been increasingly high and volatile. 

One solution to address environmental and price concerns surrounding the use of wild-sourced fish meal and oil in salmonid feeds is the incorporation of plant-based feed additives and concentrates to supplement or replace fish meal and oil.  

This approach to decreasing the environmental impact and cost of animal feed is not new or unproven. Dr. Rick Barrows, a former fish nutritionist with the U.S. Department of Agriculture (USDA), told Global Seafood Alliance in 2019 that introducing plant-based additives in feed can provide farmers with more versatility. 

“We could see a growing trend toward increasing the number of ingredients in diets and more flexibility to change diets as the price of ingredients changes. This is done all the time in terrestrial animal feed,” he said.

Further highlighting the promise of plants, Dr. Ken Overturf, a research geneticist with the USDA, was quoted in the same article as saying, “It’s worth noting that they are produced at much greater levels than fishmeal… With higher volumes, the price can be kept lower and won’t shift as much as it does for rarer commodities.”  

One reality, however, that seemingly stands in the way of the widespread use of a plant-based diets is the fact that salmonids are naturally carnivorous. Rainbow trout, for example, have typically exhibited a tendency to develop enteritis when they are fed largely plant-based diets. Sound research is needed to support a transition into these compositions so that it is done in such a way that production efficiency and animal welfare are either not impacted, or are improved, and that does not create costs that are unbearable for producers.  

The USDA’s Agriculture Research Service (USDA-ARS) has been conducting extensive and impactful research in this space through the execution of National Program 106: Aquaculture. As per the USDA-ARS website, the mission “is to conduct research and deliver technologies that improve domestic aquaculture production efficiency and product quality while minimizing impacts on natural resources.”  

This year, the USDA-ARS published an Accomplishment Report for Program 106, which covered research conducted through 2018-2022.  As it pertains to the reduction of the need for fish meal and oil in Salmonid production, research efforts and accomplishments by year can be summarized as:

2018
Researchers in Aberdeen, Idaho assessed the feasibility of using various processes to increase the protein enrichment of commercial high-protein rice flour (HPRF) and showed that these processes increased protein levels more than seven-fold.  However, the inclusion of this enriched HPRF causes animals to excrete excess phosphorous due to high phytate levels.  

The researchers also developed a wet method to process barley and oats into fractions enriched with protein, beta-glucan, starch, and other carbohydrates.  This method secured a U.S. patent and was licensed to a U.S. startup company.

2019
Completely replaced dietary fishmeal. Unlike non-selected fish, which develop enteritis on these diets, these fish do not develop enteritis and they demonstrate improved performance, as compared to conventional commercial trout strains fed fishmeal-based diets.  

In 2019, the third largest rainbow trout producer in the U.S. stocked one million of these selected fish. 

The second largest trout egg retailer in the U.S., Riverence, obtained germplasm from the USDA-ARS and is now selling eggs from these selected lines. The company is marketing these eggs as hardier and has demonstrated their improved growth rates under different environmental conditions

Researchers in Aberdeen, Idaho developed two methods for measuring trypsin inhibitors (TI) in soybean products. TIs are anti-nutritional and can cause digestive and metabolic diseases and slow growth in animals.

2020
Researchers in Hagerman, Idaho, developed an improved method for simpler and more accurate measurement of total starch and gelatinized starch in situ for wet and dried products.

2022
Feeds that substitute plant-based proteins for fishmeal can compound effluent-based problems, such as algal blooms because these feeds can reduce fecal stability, increase fecal fine particles, and add nutrients to the water. 

Researchers in Hagerman, Idaho, and Bozeman, Mo., determined that rainbow trout feeds comprised of a mixture of poultry byproduct meal, corn protein concentrate, and soy protein concentrate with guar gum binder produced more stable feces characterized by larger fecal particles and fewer fine fecal particles, compared to standard fishmeal-based and commercial feeds.

 “There are big producers, not just niche producers, that are willing to make significant changes, putting these fish into widespread production,” said Overturf, when asked to reflect on the successes in selective breeding for plant-based diets in rainbow trout to date.  “Right now, the germplasm from our selection group makes up the majority of the rainbow trout in the U.S. … The fish are out there, and the potential is there.”

With the benefits of a plant-based transition apparent, the question of why plant-based diets and plant-based friendly Salmonid strains have not become the industrial norm remains. Dr. Wendy Sealey, a fish research physiologist with the USDA, speculated on the cause. 

“The concentration methods are there, the commercialization is where we’re still struggling a little bit in the plant-based world,” she said. “What we need are cheaper methods for producing these concentrates. They are physiologically, nutritionally sound products.”

When looking to the future though, Sealey pointed out that this may shift soon, as complementary processing infrastructure is coming online across the United States.

“There is a huge number of soy crushers in the U.S. We’ve never had this many before, and this is in response to some of the bio-fuel initiatives and so that’s going to shift the ingredient market more,” said Sealey. “I think there are a lot of things that are going to happen in the near future that are going to continue to increase plant utilization in fish and a lot of them have nothing to do with how well the nutrition matches with the fish.”

Sealey added that the thing that gets her excited about the future of plant-based fish feeds is the possibilities to learn more about the classes and different products. 

“A lot of that does carry over between the different plant products, and how we can use them carries over so that we’re all getting better at how to formulate feeds… Everyone is learning to use them better,” she said.