Bits & Pieces: Fish Speed, Fish Hearing, and Lunker Genetics

Science Discoveries: Directional Hearing in Fish

Whether it’s a firecracker popping, a car horn, or a dog barking in the distance, we can tell which direction a sound is coming from. Sounds travel through the air as oscillations of motion and pressure, and humans and other terrestrial animals determine the direction of the source of a sound based on the time difference when pressure is detected in one ear versus the other.

Now, if you’re submerged underwater and someone in the area slaps the water surface, you wouldn’t be able to determine the direction of the sound’s source with any accuracy. That’s because sound travels so much more quickly underwater—about 5 times faster than in air—that we lose our ability to detect time delays in pressure from one ear to the other. Because sound underwater travels so much quicker, it would seem fish also would also have a difficult time detecting the direction of sound sources. Yet fish do have directional hearing, and several theories of how they accomplish it have been proposed. Recently, scientists have solved the mystery of directional hearing in fish.*

The scientists offer that fish have two auditory pathways that might enable directional hearing. One is the inner ear, which contains small ear bones called otoliths and hair cells, which function as a system to detect particle motion. But they explain that the inner ear only allows detection of the axis of the sound, not the actual direction it’s coming from. They term this the 180-degree ambiguity problem of directional hearing. The swim bladder, however, acts as a second hearing pathway. Gas in the swim bladder compresses and decompresses as sound waves oscillate, and a system of specialized bones (Weberian apparatus) then send signals to the inner ear.

To test various theories of directional hearing, the scientists performed tests on a very small fish, Danionella cerebrum, which measures only about 12 mm (about a half inch) long with a distance of less that 1 mm between their inner ears, making them the ultimate test subject. Tests were performed in laboratory tanks with elaborate setups, including speakers to produce various sounds, overhead cameras to trace fish movements, as well as microscopic examinations utilizing laser scanning of fish hearing structures on anesthetized subjects. To distinguish hearing in the inner ear from the lateral-line sense, which detects low-frequency water flow, directional hearing tests were replicated using fish that underwent ablations to make their lateral lines dysfunctional. Directional startle responses to sounds were analyzed, with some tests even done to trick fish by manipulating pressure waves. In those cases, fish were actually tricked into moving in the opposite direction toward the sound. Important to note that the responses were similar between the fish with functioning lateral lines and those that had non-functioning lateral lines.

Their experiments provided new evidence of directional hearing in fish, supporting a hypothesis proposed by Arie Schuijf in 1975. By controlling for pressure and particle motion, they found both cues are needed for directional hearing. While particle motion acting on the inner ear is one part of this dual sense, sound pressure also plays a role as it acts on the swim bladder, which sends signals detected by hair cells in the inner ear. This series of small bones that connects the swim bladder to the inner ear is found in 66 percent of all living freshwater fish, the researchers report.

–In-Fisherman

*Johannes, V., T. Chaigne, A. Svanidze, L. E. Dressler, M. Hoffman, B. Gerhardt, and B. Judkewitz. 2024. The mechanism for directional hearing in fish. Nature 631:118-124. https://doi.org/10.1038/s41586-024-07507-9

Ecoscience In Action: Swim Speed Results

Swimming speed varies greatly among fish species, from the sedentary meanderings of the bullhead to the blazing bursts of barracuda or salmon. Swimming speed affects strike distance as well as how hard a fish can pull against drag. Fish ecologists say that habitat, as well as feeding ecology, are important determinants of swimming speed.

Tracy Leavy and Timothy Bonner of Texas State University at San Marcos used a flume-like device to test swimming speeds (calculated as body-lengths per second) of 37 warmwater species found in streams of Texas and Louisiana.*  Most of the stream fish were minnows, 24 species in all, while blue catfish, largemouth bass, longear sunfish, redbreast sunfish, and bluegill were also tested.

And the winner is—the emerald shiner, swimming nearly 20 body lengths per second, beating the silverband shiner by a nose. Blue catfish swam a respectable 14 body lengths per second, while the sunfish species lagged. Bluegills led that group at 8.1, edging redbreasts (7.5), and largemouths (7.3).

The faster species inhabit medium to larger rivers and occupy fast-water habitat like riffles and runs. Slower fish favor slackwater spots like pools and backwater pockets. The faster families of fishes generally are more streamlined with longer pectoral fins and greater height of dorsal and caudal fins.

–Steve Quinn

*Leavy, T. R., and T. H. Bonner. 2009. Relationships among swimming ability, current velocity association, and morphology for freshwater lotic fishes. N. Am. J. Fish. Mgmt. 29:72-83.

Field Science: Genetic Links in Lunker Largemouths

Since 1986, the Texas Parks and Wildlife Department (TPWD) has conducted an operation to spawn giant bass caught by anglers in Texas waters, initially called the Share A Lonestar Lunker Program, now Toyota ShareLunker (texassharelunker.com). The first “participant” in the program was “Ethel,” a state-record 17.67-pounder caught at Lake Fork by Mark Stevenson. She became famous as a star of Bass Pro Shops Aquarium, viewed by millions of bass fans.

Ever since, largemouths over 13 pounds (labeled Legacy Class by TPWD) caught from January 31 through March 31 are brought to the Texas Freshwater Fisheries Center in Athens to spawn in controlled conditions with select male bass. Since the early 1990s, those males have been offspring of ShareLunker females spawned in previous seasons and held for several years as broodstock.

Over the years, Fishery Center staff have noted family trees of ShareLunkers, since tissue has been collected for DNA genetic testing, and scales or bones are available from the earliest ShareLunkers, from which DNA can also be extracted. ShareLunker Director Natalie Goldstrohm noted that ShareLunker (SL) #9 was caught in 1988, a 16.13-pounder from Gibbons Creek Lake. One of her daughters was stocked into Lake Fork and grew into SL #184, caught in 1994, as she had grown to over 14 pounds. One of her offspring (SL #305), exhibited her grandma’s and mother’s inclination toward large size, as she was caught at Fork in 2000 at 14.67 pounds. Her daughter (SL #365) was caught at Fork at 13.19 in 2009. The family trait for size continued into the next generation, as SL #578, the great granddaughter of SL #9, was caught at a TPWD Research Lake by bass pro Gary Klein who had been invited to fish there.

“Five generations of ShareLunkers is the record so far,” Goldstrohm says, “but we’ve found many other close familial ties. SL #567 and #625 are sisters, spawned at the Texas hatchery, daughters of SL #446 and granddaughter of SL #371. They’re one of the five pairs of sisters to reach ShareLunker status.”Goldstrohm also points out the contribution of male broodfish, the sons of ShareLunkers, to later generations of giants. “Males that were ShareLunker offspring contributed to four generations out of the five I mentioned earlier,” she says. “The male paired with SL #9 was unknown since none were available yet.

“We call the offspring of ShareLunkers ‘Lonestar Bass’ and we’ve greatly expanded the stocking of fingerlings in more waters, so we expect further production of huge bass for Texas anglers and visitors. Genetically, just over 50 percent of ShareLunkers are pure Florida bass. About seven percent are F1 (first-generation) hybrids. Only 3 percent show a majority of northern bass alleles. We’re learning more about the genetic backgrounds of big Texas bass, as we have a program in which anglers collect three scales from bass over 8 pounds or 24 inches and send them to us with catch information. We can extract DNA from the scales and decipher heritage.” 

–Steve Quinn

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