Zebrafish have long been used as animal models for human research for many reasons, including that we share a similar genetic structure and have the same major organs and tissues. Researchers can also manage many factors that may influence behavior, such as diet, age, and sex of the fish—things not so easily controlled in humans.
“Back when I was studying for my master’s degree at the University of Glasgow in Scotland, I researched how to exercise Arctic charr held in aquaculture facilities to increase the quality of their muscle growth. I enjoyed that work, and the idea of how I can influence fish behavior as a result of exercise stuck with me.” Eleven years later, Cairsty DePasquale is still studying fish, although the scope of her work has shifted. She has been an assistant professor of biology at Penn State Altoona for five years, and in that time, she has conducted multiple studies on fish. Her current research uses the tropical, freshwater zebrafish as a proxy for the human brain to determine how exercise can impact it.
Penn State Altoona engineering faculty recently finished constructing a swim tunnel for the research that can hold about 40 fish. The tunnel, essentially a treadmill for the zebrafish, has 40 different channels. In each channel, water flow can be controlled separately. DePasquale and her research assistant, Jordan Wolfkill, are just beginning the process of administering tests.
They start by taking the fish from their home tanks and putting them into the swim tunnel. The flow of the water is increased incrementally at different rates in each channel until what is called a critical swimming speed, or U(crit) level is reached and the fish begin to fatigue. Then, the pair can look at changes in behavior and cognition. “One way to look at fish cognition is to put them in mazes and watch them complete the maze to get food or find their shoal mates. The fish are able to use different landmarks in their environments, like plastic plants if we place them in different parts of the maze, to navigate through.”
Another type of learning DePasquale is hoping to look at is spatial pattern separation. In humans, an example would be like trying to remember where you parked your car when you leave work every day. Imagine you park it in the same parking lot, but a different parking space each day. It’s often hard to remember day-by-day where you parked your car. This is called spatial pattern separation—trying to separate similar, yet slightly distinct memories. This can be measured in fish by using what is called a Radial Arm Maze and use food as the cue instead of a car.
The idea behind the research is to fill in the gaps where research on humans and rodents is lacking. “We are better able to control duration, frequency and intensity of exercise with fish than we are with humans and rodent models, so we will have a better picture of how exercise changes the brain and behavior. We can then use these results to make inferences about what is happening in humans, because there is quite a bit of overlap in terms of how a fish brain works compared to the mammalian brain.”
A second prong of DePasquale’s research involves determining whether exercise physiology can be used on fish to improve their welfare and survival rates in the wild. “People tend to think only of the cute cuddly pandas, the dolphins, and other charismatic animals, but there are a lot of fish populations that are declining, and we need to understand how better to conserve them. Each different population of animal is dependent on the other. It's a web of different animals that are surviving together. If one population declines, that tips the balance.” DePasquale points out that the survival rate of fish released from hatcheries is low, so, in theory, if fish were exercised in a hatchery environment before their release, perhaps they would be better equipped cognitively to survive. “I just like the idea of how we can apply exercise physiology to problems that we have with fish welfare and populations in the wild.”
Because this is a long-term goal, DePasquale is still considering options on how to develop this area of her research. She would love to work with local hatcheries to create an exercise program for fish that are going to be released. Hatchery fish, such as salmon and trout, are typically held in large tanks in high densities so a flow of water could be introduced into some of the tanks to force the fish to swim. Upon release, survival rates can be compared to the fish that did not receive exercise. DePasquale surmises that the fish forced to exercise would have greater survival rates thanks to muscle growth and cognitive development from the exercise.
DePasquale enjoys having the opportunity to continue her research at Penn State Altoona and to include students in her work. “I love doing research here and being able to mentor undergraduates through the research process. They are a little apprehensive when they first come in, but they get into a rhythm of understanding how to look after the fish, how they behave, and what influences fish behavior. I love seeing that growth in students.”
Wolfkill, a biology major and chemistry minor, is grateful for the chance to conduct research and the experience it provides. “I feel very fortunate to be a part of this. It’s really engaging and interesting work, and I love how many hands-on things I get to do. It’s all so valuable to my education.” Wolfkill would eventually like to conduct research in his professional career and thinks this is a great foundation to prepare him for that.
Both Wolfkill and DePasquale enjoy the process of research and the thought and skill behind it. Says DePasquale, “It's the challenge of every day being different and not knowing what's going to happen. You don't know what the results are going to show you. You can make predictions but ultimately it's the animals making decisions. I like the challenge, I like the idea of always discovering new things. I'm constantly reading new literature and figuring new things out all the time.”
DePasquale says she would like to continue this research and involve more students. The research doesn’t have a deadline, and there are many variable and open-ended ways to study the fish. She was recently awarded a grant through Penn State’s Center for the Study of Sports in Society that will aid in her work. In collaboration with faculty in Penn State Altoona’s engineering department, DePasquale is in the process of building a more sophisticated swim tunnel that can more accurately control water velocity. A portion of the grant money will used to build new mazes and ways to test fish behavior.
As the research continues and data becomes available, DePasquale says she would ultimately like to get the findings published in peer review journals. Students will also be able to present the research at the Penn State Altoona undergraduate research fair held every April, and at regional and national conferences so that results are easily accessible to the scientific community and the general public.