By: Adrienne Flowers
Most of us consume seafood without questioning what our seafood had for dinner. With funding from the Mississippi-Alabama Sea Grant Consortium, scientists at Auburn University, in collaboration with Hubbs SeaWorld Research Institute and the Alabama Marine Resources Division, are learning how dietary taurine, an essential amino acid, improves the health, growth and survival of California yellowtail and Florida pompano.
Researcher Guillaume Salze, Ph.D., and Professor Allen Davis, Ph.D., of Auburn University addressed important knowledge gaps in aquaculture research by investigating the impact of taurine supplementation on broodstock and larval fish. They investigated the impact of taurine supplements on broodstock (mature fish used in aquaculture for breeding) and their larval offspring to address gaps in aquaculture knowledge.
Their efforts played a key role in securing approval from the American Association of Feed Control Officials (AAFCO) for allowing synthetic taurine supplements in fish feeds, a move that allows people who raise fish to have more options. Now U.S. manufacturers can produce fish feeds that are more sustainable, provide better nutrition at a lower cost and are more competitive in a global marketplace.
Why does taurine matter?
Taurine is an amino acid. It is an essential nutrient for many fish species. In the wild, fish get taurine from eating other fish or aquatic animals, such as clams and shrimp. It is absent from most plant sources. Taurine benefits people, too, which is why it is readily available in baby formula, over-the-counter supplements and some energy drinks.
Effects of taurine status in fish broodstock
Prior research showed improvements in growth and survival of larval and juvenile fish when consuming taurine-supplemented feed and reduced growth and survival when there is a taurine deficiency. Nutrition research on broodstock involves a different focus, according to Salze.
“The goal is to have them reproduce effectively, to produce a lot of eggs and to produce a lot of high-quality eggs that will lead to high-quality larvae,” he said.
Salze and his colleagues focused on the effect of amino acid composition of fish feed and how it affects broodstock maturation and reproduction. Most research emphasizes the role of lipids (omega-3s, for example) in broodstock nutrition, while less research highlights amino acid requirements. Salze’s group showed that broodstock produced more eggs when they received taurine supplements. Taurine also improved larval quality.
In the California yellowtail experiment, there was no difference in the hatching rate between taurine-supplemented and standard broodstock. However, there was a significant improvement in the number of larvae that survived to first feeding, the point at which the larvae have resorbed their yolk sac and start feeding on external food particles. This improvement stemmed from supplementing the broodstock diet with taurine, Salze said.
When Salze’s group compared survival, they saw zero survival in standard larvae that came from standard broodstock—in other words, no taurine supplementation at all. These broodstock produced eggs and larvae, but none of the larvae survived to 20 days. Researchers saw this result over two years of rearing fish.
Another interesting outcome, and one that surprised the research team, was that the double supplementation (taurine-supplemented larvae from taurine-supplemented broodstock) survived well, but they were smaller overall by the end of the larval cycle when compared to their counterparts. Embryos and larvae survived when the broodstock, the larvae or both received taurine supplementation. And, when both received taurine, it negatively impacted growth of the fish.
“There was no impact on egg morphometrics (size and shape) or composition,” he said. “The measured differences were in the embryonic and larval stages.”
These findings have broad implications for aquaculture. Taurine supplementation usually has beneficial effects, especially in marine species that are highly carnivorous.
“Given what we see in larval and juvenile stages, it makes sense to supplement broodstock,” Salze said. “From what we see in yellowtail, I would not be surprised if supplementing broodstock would benefit other species.”
U.S. manufacturers can compete in the global market
U.S. companies can now use synthetic taurine in their feeds due to this Mississippi-Alabama Sea Grant Consortium-supported research team and their partnerships.
The process to change fish feed regulation was a five-year endeavor. In the Alternative Feeds Initiative-The Future of Aquafeeds (https://spo.nmfs.noaa.gov/sites/default/files/tm124.pdf ), the National Oceanic and Atmospheric Administration and the U.S. Department of Agriculture named taurine as an important nutrient for fish that is absent from plant-based feed sources, recommending it as a focus for nutritional studies.
In 2012, a process began with collaboration among various research groups to gather scientific data to support the safety and efficacy of taurine as a feed ingredient. Their work led to a petition presented to the AAFCO and the U.S. Food and Drug Administration (FDA). In early 2017, regulators officially adopted a definition of synthetic crystalline taurine that included it as a nutritional supplement for fish foods.
Approval of synthetic taurine removed a roadblock for the United States in terms of being globally competitive. Prior to approval, fish feed produced in the United States depended on ingredients, such as fish meal, squid meal, fish oil and poultry byproducts, to deliver essential nutrients. These ingredients are not sustainable and can be very expensive.
“In the big picture, this work is about having more resources available to aquaculture experts,” Salze said. “Fishmeal is an expensive ingredient, and it comes with economic and environmental costs. Removal of animal proteins from fish feed and replacing those with plant proteins, such as soybean, is a good strategy. Being able to supplement feed with synthetic taurine is one piece in this complex puzzle.”
Other individuals collaborated with Salze and Davis on the broodstock research, including Mark Drawbridge and Kevin Stuart of Hubbs SeaWorld Research Institute, Kevin Anson of the Alabama Marine Resources Division, and Kevan Main and Nicole Rhody from the Mote Marine Laboratory. Also, Delbert Gatlin of Texas A&M University, Gibson Gaylord of the U.S. Fish and Wildlife Service and Ron Johnson of NOAA Northwest Fisheries Science Center contributed to the petition for approval of taurine.
Source: Mississippi-Alabama Sea Grant Consortium