UW Student Examines How Salinity and pH Impact Wyoming Fish Page Title
Maya Gilmore, University of Wyoming Extension
Miles Milbrath became a master’s student in UW’s zoology and physiology program in January 2025—but before he’d even earned his bachelor’s degree, he’d already published a scientific paper in an international, peer-reviewed scientific journal.
Milbrath’s first paper, “Evaluating How Growth and Diet of Native Freshwater Fishes Change in Response to Salinity and pH in a Semi-Arid Landscape,” examined how harsh conditions impact native Wyoming fish. It was published in 2025 in the journal Fishes.
He was the lead author of the paper. Co-authors were Audrey Lindsteadt, UW doctoral student, and Lusha Tronstad, lead invertebrate zoologist for UW’s Wyoming Natural Diversity Database and an adjunct faculty member in the Department of Zoology and Physiology.
Milbrath conducted his research through the Wyoming Research Scholars Program (WRSP). WRSP pairs undergraduate students with faculty mentors, giving students a chance to participate in hands-on scientific research and connect with established scientists.
Mussels, beetles, and intermittent streams
In 2023, Milbrath began working in Tronstad’s lab as a student researcher supported by WRSP. For his first project, he helped graduate student Samantha Poratti study freshwater mussel populations in the Bear River watershed in southwest Wyoming.
During his second summer with WRSP, Milbrath helped Lindsteadt survey the distribution of rare aquatic beetles throughout Wyoming. As the researchers traveled through the state, they encountered fish living in very saline intermittent streams.
Agricultural runoff, road salts, and warm, dry weather have gradually made waterways throughout Wyoming more saline as additional salts concentrate in smaller amounts of water. Intermittent streams, which flow when there’s heavy precipitation but disappear completely during drier months, are particularly prone to salt concentration. Milbrath decided to study how these harsh conditions affect the few fish that live in these pools.
Surviving, not thriving
Most of Wyoming’s native fish are adapted to a neutral pH and very little salt. In contrast, some of the salty pools where Milbrath found fish were almost as salty as the ocean and had a high, or basic, pH.
Milbrath studied two of Wyoming’s native fish known for tolerating harsh environments: the northern plains killifish and fathead minnows. Unlike commonly fished game species like trout, these fish are found in both fresh and saline water.
“By no means are they super abundant, and I wouldn’t say they’re thriving, but they’re able to survive these environments,” says Milbrath.
He found that the fish did not grow as quickly when the water had more salt or a higher pH. That’s probably because these fish had to direct more of their energy toward survival, Milbrath explains.
He also examined the fishes’ diets. In more saline, higher-pH water, prey was less available. While there was significant variability, the fish in these harsher pools had a more limited diet and were more likely to have empty stomachs.
These diets likely have a negative impact on fish health in the long term, especially in combination with the other environmental stressors fish experience in these pools.
Changing waterways
Milbrath found some pools that were about twice as salty as the ocean; no fish were living in these pools.
Many fish use intermittent stream habitat to lay their eggs and to move throughout the state. As some of these pools become too salty to survive, fish lose vital habitat.
Milbrath’s research demonstrated that even killifish and fathead minnows, some of Wyoming’s most resilient native fish, struggle with high salinity and pH. Other fish species may simply die off as Wyoming’s waterways change.
“Since we have the ability to alter ecosystems so substantially, we have a duty to go in and make sure that these fish are protected,” says Milbrath.
The power of mentorship
Milbrath is passionate about protecting all the life forms that rely on Wyoming’s waterways, even the ones that are often overlooked. In March 2026, he published a second scientific paper based on the research he conducted with Poratti on Wyoming’s native mussels. As a master’s student, he is now studying how man-made beaver dams affect fish, macroinvertebrates, food webs, and water quality.
Milbrath believes his research as an undergrad has helped him succeed as a graduate student. The Wyoming Research Scholars Program connects undergraduates not just with faculty, but also with a community of passionate, knowledgeable graduate students, he says.
“Working with grad students early on was one of the most influential factors starting out in my academic career,” he says. “It can be really a helpful step so you’re not figuring it all out while you’re in your master’s or your PhD.”
In his first year as a master’s student, he mentored a WRSP undergraduate himself, sharing his passion for ecological research with the next generation of WRSP scholars.