Dr. Dong-Fang Deng: Researching Aquaculture Nutrition

Meet Dong-Fang. She’s a nutritionist researching better fish feeds to support the aquaculture industry and conservation efforts. Dong-Fang works with students ranging from high school interns to international postgraduates. Her dynamic team learns from one another as they tend to many species of fish—including yellow perch, rainbow trout, Atlantic salmon, tilapia, and even lake sturgeon—in the School of Freshwater Sciences’ extensive aquaculture lab.

One of Dong-Fang’s projects is to optimize fish feed to meet the specific nutritional needs of yellow perch. Since the Great Lakes species popular for the traditional Wisconsin fish fry has taken a hit in recent decades, there’s been interest in farm-raising yellow perch, but fish diets developed for other species are not ideal for perch metabolism. Feeding perch with food developed for raising salmon or rainbow trout results in “big bellies, lots of visceral fat,” Dong-Fang says, “which means the nutrients from the diet—some of them just go to the waste product. Long-term wise, maybe it’s also not good for their health as well. So what we try to do here is optimize the feed recipe based on the nutrient requirement of this fish.”

Another challenge Dong-Fang’s lab is working to address involves decreasing mortality for very young perch. Larval perch are tiny and frail. Often only 5% to 10% of new hatchlings survive to adulthood in captivity. Increasing the survival rate is critical to support large-scale aquaculture that makes business sense for would-be farmers and their investors. “We need to have enough fingerlings—young fish—for the industry people to raise up for food. That’s one of the bottlenecks we need to solve,” Dong-Fang says. “In our lab, we try to work out not only the feed but also the culture system. Because if you have seen the perch baby before, it's like an eyelash! Very tiny! It’s hard to push this baby to eat a pellet food. They can’t swim a lot. Even one centimeter could be a long distance for them. We try to integrate how the culture system and how the food work together to help them survive.”

Dong-Fang’s lab pays a lot of attention to yellow perch. She’s also involved in the effort to package the right diet for fast-growing perch, the result of selective breeding with fast-growing parents. “Otherwise the potential won’t show up,” she says. Without the right nutrients in the right proportions at the right time, those good genes can go to waste.

Dong-Fang’s research is also important in terms of addressing global aquaculture issues.

As the human population continues to grow and global fisheries face further stress, aquaculture is expected to become an increasingly significant part of humankind’s portfolio of food strategies. Fish are nutritious and—relative to other animal protein sources like cattle or pork—require less feed to produce the same amount of product. But there’s a catch. Most fish feed comes from wild-caught fish. In order to raise fish sustainably, alternate protein sources for fish feed are therefore in high demand.

Dong-Fang notes that much research has been done exploring soybeans and corn as a “next generation” fish food, but the drawback to relying on those crops is they require a lot of land, energy, and water. Dong-Fang and her lab are interested in exploring other fish meal alternatives, including algae, duckweed, food waste, or even insect protein. Dong-Fang’s current research in 2020-2021, funded by the U.S. Department of Agriculture, explores alfalfa leaf protein. If this strategy proves viable, she notes it would help both the aquaculture and agriculture industries by dramatically expanding the market for alfalfa crop.

She finds her work motivating. “If you feel that your work can help out society, can help out the industry,” she says, “you have the passion.”

She shares that passion with students working in her lab. Her research also connects her students with other scientists and professionals in the aquaculture and agriculture industries. Students get hands-on experience working in a fish lab and also learn how that research is applied to the efforts to scale up sustainable aquaculture enterprises. Questions and ideas from farmers, Dong-Fang says, can help focus and guide new research questions that are needed to advance the aquaculture industry.

Dong-Fang grew up on a tropical island in China where she was surrounded by fish. Eating wild-caught fish for any meal was common. In college, her professor introduced her to dissecting a fish and she was fascinated by the differences in fish intestinal tracts. This curiosity ignited a passion that led her to multiple degrees involving aquatic nutrition. She’s studied in China, California, Mississippi, and worked as a research scientist for several years at The Oceanic Institute of Hawaii Pacific University studying shrimp before finding a home at the School of Freshwater Sciences in 2015.

“With the Great Lakes we are very fortunate to have this rich freshwater resource…” Dong-Fang reflects. “I think I ended up in the right place at the right time.”