Observing Otoliths | Ohio Sea Grant

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Observing Otoliths

12:00 pm, Tue March 26, 2024 – Otoliths — and the ability for fish to hear sounds and detect predators — are the subject of newly funded Ohio Sea Grant research studying fish species raised in captivity

Do fish have ears? Yes, and while they might not be visible on the outside, their inner ears contain tiny, stone-like structures called otoliths that help them process sound.

Otoliths — and the ability for fish to sense sounds and detect predators — are the subject of newly funded Ohio Sea Grant research project looking at trout and salmon species raised in captivity. The goal is to ensure fish aquaculture in the state is both efficient and humane.

“Fish that are raised in captivity oftentimes develop a different type of calcium carbonate in their otolith,” said Dr. Kevin Neves, an associate teaching professor in Bowling Green State University’s Department of Biological Science who is leading the project. “So we started looking at what is causing these otoliths to change and more importantly what the impact is.”

Watch Dr. Neves discuss his upcoming research on steelhead trout.

Neves, alongside Bowling Green researchers Drs. John Farver and Jeffrey Miner, will study these impacts in salmonid species of fish raised in hatcheries and commercial fish farms. The project is a part of Ohio Sea Grant’s 2024-2026 research grants program.

Otoliths are found within a fish’s cranium, where they sit on nerves that detect disturbances created by soundwaves vibrating through the fish. The structures grow throughout a fish’s lifetime in proportion to their length and accumulate a certain form of calcium carbonate: aragonite.

However, researchers found that large proportions of fish raised in captivity under “high stress” conditions tend to have deformed otoliths with a different form of calcium carbonate called vaterite, potentially affecting their hearing. Why this occurs is unknown, Neves said.

“State hatcheries, for example, will release millions of juvenile trout for fishermen to catch, and oftentimes there’s a really low return rate of these fish to streams later in life,” he said. “These fish with vateritic otoliths may not be able to detect sounds, which might be causing them to be more susceptible to predation in the lake before returning to streams.”

Through the upcoming project, Neves’ team will examine why fish otoliths develop vaterite instead of aragonite, the role crowding and environmental conditions might play, and how these otolith changes affect fish predation risk and rates of return to the mouths of tributaries each year.

a round shape with many rings inside of it

A cross-section of a fish otolith taken by researchers at Bowling Green State University. Otoliths are calcium carbonate structures found inside the heads of bony fish. Each fish has three pairs of otoliths, which vary in shape and size.

Starting this spring, researchers will collect steelhead trout returning to various tributaries of Lake Erie to check the proportion of fish with normal and abnormal otoliths. Others will conduct stomach content analyses of trout predators to look at the effects of predation. Then, in the fall, researchers will perform laboratory experiments on fish to see what specific conditions, such as carbon dioxide levels or temperature, might be causing abnormalities.

“We’re hoping to identify what actually causes the fish to develop their otoliths as vaterite because that will allow for more efficient and humane production of fish,” Neves said.

Findings from the study could benefit Ohio’s fisheries as a whole as well, Neves said, including those stocked by the Ohio Department of Natural Resources Division of Wildlife’s six state fish hatcheries.

“To have a higher return of fish coming back means that the fishery will essentially be more effective,” he said. “People will have more fish to catch as they come back into the rivers, and those programs will be deemed as more successful.”

For more information about this ongoing research, contact Dr. Neves at

Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.

ARTICLE TITLE: Observing Otoliths PUBLISHED: 12:00 pm, Tue March 26, 2024 | MODIFIED: 3:01 pm, Wed March 27, 2024
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Alex Meyer
Authored By: Alex Meyer