Fish help keep us healthy. The least we can do is return the favor.

Like any other farmers, fish farmers face challenges in keeping their stock disease-free, because the production environment is more stressful for animals than their natural environment is. Unfortunately, the few antibiotics and chemicals approved for treating sick fish can be pricey, often don't work, and may pose environmental concerns.

Jesse Trushenski, a doctoral student in zoology, and Chris Kohler, zoology professor and director of SIUC's Fisheries and Illinois Aquaculture Center, want to produce naturally healthier fish through nutrition. Their research suggests that augmenting fish feed with a certain form of vitamin E can help fish resist disease.

For their test case they're using hybrid striped bass, a popular aquaculture fish that Kohler's research team has worked with extensively. Compared to more-tolerant species like catfish, these bass are nervous Nellies, easily stressed and therefore more vulnerable to disease.

The research, which began as part of a $600,000 National Science Foundation Partnerships for Innovation grant to develop new fish feeds, has been done in collaboration with Archer Daniels Midland Co. Trushenski also won a two-year, $60,000 fellowship from the National Sea Grant College Program to support the work.

Most vitamin E supplements that we buy at the drugstore contain a synthetic version of a type of vitamin E called d-alpha tocopherol. Trushenski has been studying the nutritional effects of a naturally derived d-alpha that Archer Daniels Midland makes from soy.

Natural d-alpha has a molecular shape perfectly fitted to the protein in the body that grabs vitamin E and ferries it to body tissues. The synthetic form has a mix of molecular shapes, some of which don't fit the protein and are simply excreted.

Trushenski and Kohler were intrigued by studies with other species, including humans, indicating that the natural form of d-alpha can boost the immune system.

Trushenski's first experiments with the hybrid striped bass established their minimum nutritional requirement for vitamin E using the natural form rather than the synthetic form. The natural form was almost three times as potent in the body, she found.

She then raised groups of bass on six different diets: a control diet with no natural vitamin E, and experimental diets with one, two, five, 10, and 100 times the minimum requirement. Within each group, some fish were left at their leisure, while others were subjected to various stress levels (being chased with a net for one minute or confined submerged in a net for an hour). In a second, similar experiment, other groups of fish faced a different stressor: "working out" in a swim tunnel, the fish equivalent of a treadmill.

Blood chemistry analysis indicated that the fish on the enhanced diets held up to the stress better:

• Macrophages (immune cells) taken from some of these fish were better able to kill bacteria.

• Lysozymes (an enzyme in the blood that breaks up pathogens) taken from the fish were up to 25 percent more effective at killing pathogens in lab cultures.

• The activity of prostaglandins, hormones that regulate metabolism and influence immunity, was boosted.

The diet containing five times the nutritional requirement for natural vitamin E had the optimal effect on these markers for improved immune function. Although vitamin E is known for its antioxidant properties, other properties of the vitamin appear to be responsible for the changes, Trushenski says.

But are they biologically significant changes?

To find out, Trushenski is running a "real-world" test with fingerling hybrid striped bass. She's raising fish on four different diets: feeds with one and five times the nutritional requirement for synthetic vitamin E, and feeds with one and five times the requirement for natural vitamin E. After 12 weeks, she'll expose all of the fish to a common fish parasite and compare the rates and severity of infection in the four groups.

If the findings look good, researchers in other areas may be interested too.

"In terms of lipid [fat] metabolism, fish would be a great experimental model for human nutrition studies," says Trushenski. "A lot of what we're doing has implications for human health."

—by Marilyn Davis