The US Department of Agriculture National Institute of Food and Agriculture has awarded two grants totaling $1.15m to the Texas A&M research.
Hybrid striped bass are the fourth most farmed fin fish in the US, behind only catfish, salmonids, and tilapia.
The work will be led by Guoyao Wu, College of Agriculture and Life Sciences University Distinguished Professor and Texas A&M AgriLife Research Faculty Fellow in the Department of Animal Science.
Collaborating with Wu on one study is Delbert Gatlin, Regents Professor in the Department of Ecology and Conservation Biology, Bryan-College Station, Texas A&M. The scientists are set to assess the biosynthesis and nutritional roles of glycine in hybrid striped bass.
On the second study, Wu will collaborate with Mike Criscitiello, professor of veterinary pathobiology and associate dean for research and graduate studies in the College of Veterinary Medicine and Biomedical Sciences, Texas A&M. They will examine the impact of dietary glutamate on the development of gut mucosal immunity in hybrid striped bass.
The scientists believe both glutamate and glycine should be considered functional amino acids in animal nutrition. They are the cheapest amino acids, and yet hold great promise as cost-effective feed additives, remarked Wu.
Finite supplies of marine resources
Fishmeal and fish oil production are environmentally and ecologically sustainable, Gatlin said. Their production has not varied much over the past few decades, and both have rather good life cycle assessments compared to other feed resources, he argued.
“However, their supplies are limited, so as world aquaculture is projected to continue growing, the costs of these marine ingredients are expected to increase,” he said. “So, there will likely be greater need to substitute larger portions of fishmeal and fish oil in the diets of various fish species, especially the ones with more carnivorous natural feeding habits. Thus, our project should allow greater flexibility in formulating diets to meet the nutritional requirements of hybrid striped bass without relying on fishmeal or other feedstuffs.”
While there has been a growing interest in using plant proteins such as soybean meal to replace fishmeal in farmed fish feed, success has been variable, said Wu.
“We found that glycine, the most abundant amino acid in the body of fish and fishmeal, is relatively low in plant proteins,” Wu said. “Based on results of our preliminary study, we believe that dietary glycine plays an important role in hybrid striped bass growth by maximizing protein synthesis, antioxidative capacity and creatine production in their tissues.”
Glutamate, the second most abundant amino acid in the body of fish and fishmeal, acts with glycine to promote metabolic processes, they explained.
It is a precursor of glutathione, an abundant antioxidative substance, and a major metabolic fuel for the intestinal mucosa, said the researchers. So glutamate is crucial for intestinal integrity and health. However, for over a century, glutamate had been regarded as a nutritionally nonessential amino acid in fish and other animals, they noted.
“Based on results of our preliminary study, we believe that dietary glutamate plays an important role in the development of the intestinal immune system in hybrid striped bass,” Wu said. “We expect glutamate to increase the production of anti-infectious and antioxidative molecules by immune cells in the intestinal mucosa of the fish.”
Additionally, he said, the ability of mucosal immune cells to use glutamate for energy production increases with age as the cells mature.
“Our findings will have a significant impact on US aquaculture by generating new fundamental knowledge about glutamate in improving intestinal mucosal health and survival of hybrid striped bass,” Wu commented. “The findings will also provide a new nutritional method for the use of glutamate as an adjuvant in vaccine development for the fish.”
Besides glutamate, fish also require a large amount of glycine for growth and health. And like glutamate, glycine had also long been regarded as a dispensable nutrient in animal diets, they reported.
However, Wu believes that the supply of glycine in fish diets may have a crucial role in converting feed into body protein.
He and Gatlin will determine how glycine and creatine are synthesized in different fish tissues. This team will also study the roles of glutathione and creatine in mediating the effect of glycine in diet to improve growth, anti-oxidative responses, intestinal integrity, metabolic health, and immunity in the hybrid striped bass.
Additionally, they will look to determine the role of the target of rapamycin, which is the master regulator of protein synthesis, and autophagy/proteasomes in mediating the effect of dietary glycine to promote protein synthesis and inhibit proteolysis in fish tissues.
“Skeletal muscle is the major site for creatine synthesis from glycine in hybrid striped bass,” Wu said. “Glycine activates the target of rapamycin cell-signaling pathway to promote protein synthesis in skeletal muscle, all while reducing intramuscular protein breakdown via the autophagy/proteasomes pathways. This promotes muscle growth.”
Wu said that, according to their preliminary findings, adding 2% glycine to soybean meal-based diets can replace 45% fishmeal in hybrid striped bass diets.