Research Highlights
Kentucky Researcher Works to Improve Soy Meal as Feed for Commercially Raised Fish

Hybrid striped bass juvenile. Photo: Waldemar Rossi

By Carol Brown

The United States is one of the largest seafood markets in the world, according to the Soy Aquaculture Alliance. And it is a growing U.S. industry, working to meet consumption demand with domestically raised fish and seafood.

In facilities that raise freshwater and saltwater fish for human consumption and for lake-stocking, fish need feed just like any livestock operation. But what do fish eat? For fish raised commercially, fishmeal is regarded as the most nutritious protein feedstuff, but fish are needed to make fishmeal. Over the last few decades, availability of fishmeal produced from forage fish stocks has been stagnant and prices for it have escalated. Both aquaculture and crop researchers have been exploring fishmeal alternatives for years and the soybean has risen as a prime choice. 

Waldemar Rossi, an assistant research professor at Kentucky State University’s School of Aquaculture and Aquatic Sciences, has been researching how diet formulations containing soybean meal can be fine-tuned to enhance digestibility in commercially raised fish. This project, as well as several of his other aquaculture projects, are supported by the Kentucky Soybean Promotion Board.

“Soybean meal is a high-quality protein ingredient, however there are some anti-nutritional factors that go against the digestibility of protein by some fish. Plant-based formulations also contain non-starch carbohydrates that fish are unable to digest. We are looking at exogenous enzymes to help improve digestion,” Rossi says.  “We are supplementing a mixture of different enzymes that break down some of the non-starch carbohydrates and assist in protein digestion.”

The exogenous enzymes have been developed and used in the swine and poultry industries for decades, Rossi says. The aquaculture industry is expanding research for development of these enzymes to improve the nutritional value of plant-based diets in fish as well. 

“We already know, based on previous research, that soybean meal can provide more than 50 percent of the total protein in the diets of many fish species, including the hybrid striped bass, which is the species we’re using in this project,” Rossi says. “The goal is to optimize the diet to enhance its nutritional value to the fish.”

Rossi and his students are conducting two feeding trials, evaluating the effects of diets containing carbohydrase and protease enzymes in different combinations and levels for the hybrid striped bass. One trial focuses on digestibility and the other looks at fish growth and feed efficiency. The trials began in 2020 but were delayed due to Covid-19. Rossi is hopeful the outcomes will show improved performance of the plant-based formulations using particular amounts of enzyme additives. 

“We are looking at performance of the fish, but as the aquaculture industry intensifies, we are also looking into providing nutrition solutions that help to support a more environmentally friendly industry,” says Rossi. “We are trying to minimize the amount of nutrients that enter the water as fish waste.”

Kentucky State University research assistant Kasondra Miller (left) and graduate student Michelle Loftus work on fecal matter collection of hybrid striped bass. The fecal matter helps the researchers with soybean meal enzyme additive digestibility determination.  Photo: Waldemar Rossi

As in swine, poultry and other livestock industries, producers must deal with manure, which can be physically moved and used as crop fertilizer. Fish also have waste, which enters the water in which they are raised. By refining soy-based diets to be as highly utilized by the fish as possible, less nutrients could be expelled as waste.

“Many aquaculture operations are in open waters and they are increasing production in open waters, even the sea,” he says. “The nutrients that aren’t digested and absorbed by the fish are exiting and being received by the water. We are paying close attention to this as well.”

With facilities producing fish and shrimp indoors using recirculating systems, there are advantages, Rossi says, including minimum use of water for production and the ability to remove solids and dissolved nutrients from the water, allowing control over the waste. But in these situations, producers also need to use nutritionally balanced and highly digestible feeds to reduce the amounts of solids, nutrients and metabolites entering the system.

“In these systems, excessive amounts of fish waste can be overwhelming and reduce production capability,” he says. “For these scenarios, we are trying to optimize the feed to have as low as possible output of waste.”

A priority of the Kentucky Soybean Promotion Board is to find new uses for soybean meal in the U.S. and aquaculture is a promising industry for farmers. 

“Our research aligns with the board’s priorities,” Rossi says. “We’re providing baseline research on the optimum levels of soybean meal and specific additives in commercial feeds for the aquaculture industry. This is information feed companies need so they know how much soybean meal to include in feeds, and the extent to which the use of enzyme additives may help to enhance nutritional quality, ultimately increasing the utilization and market for soybeans.”

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.