Art Hasler, Bluntnose Minnows and How Salmon Get Back Home

Happy Fish Fry Day! It’s the day that, like restaurants across Wisconsin, we put fish on our menu. Today’s main course – bluntnose minnows.

Bluntnose minnow on "Fishes of Wisconsin" poster. Photo: Marilyn Larsen
Bluntnose minnow on “Fishes of Wisconsin” poster. Photo: Marilyn Larsen

As we tackle the “Fishes of Wisconsin” challenge, striving to write a post for each of the 183 species of fish found in Wisconsin, one might expect to stumble across a species that, well, just isn’t all that interesting.
I’m happy to report that the bluntnose minnow is NOT that species. In fact, it’s the second species of minnow in as many weeks with connections to an iconic historical figure in our field of study.
Bluntnose minnow.
Bluntnose minnow.

Sure we could tell you that ol’ Pimephales notatus is very likely the most common freshwater fish in the eastern half of North America. We could divulge what it eats and what eats it. Or discuss the new look it gets during the breeding season. But the important thing here is to know that, like many fish, the bluntnose minnow follows its nose.
And that nose played a pivotal role in Art Hasler’s discovery of how salmon return to their natal streams to spawn.
Flash back to the spring of 1945. World War II is over and Art Hasler, a well-established limnologist from the University of Wisconsin-Madison, is serving his country, cataloging the damage done to research stations and laboratories and other scientific edifices as a member of the U.S. Air Force’s Strategic Bombing Survey.
In Salzburg, Germany an American jeep pulls up to the cottage that Professor Karl von Frisch, a scientist well-known for his work on the sensory abilities of animals like fish and bees, fled to when his Munich home was destroyed. Von Frisch just so happens to be a “scientific hero” of Hasler who is, of course, the man in the jeep. Thus begins a long and fruitful friendship. (Funt fact: von Frisch went on to win a Nobel Prize in 1973).
Later that year, Hasler returns to Madison, Wisconsin still pondering the question of fish sensory physiology and, with his students, launches into research on the topic.
Art Hasler. Perhaps pondering how salmon get back home. Photo: CFL Archives
Art Hasler. Perhaps pondering how salmon get back home. Photo: CFL Archives

Around this time, Hasler developed his fascination with the homing instincts of salmon. How in the world, he wondered, does a fish head out to the open ocean, swim around for thousands of miles as it grows up, then head back to the exact place where it hatched out of an egg?
According to Hasler’s obituary in The New York Times, a 1946 hike pointed him in the right direction:

Serendipity led Dr. Hasler to explain how migrating salmon find their way back to their home streams to spawn. Hiking near his birthplace in Utah in 1946, he had a homing epiphany.
At a waterfall, the fragrances of mosses and columbine enveloped him, evoking forgotten memories. And he wondered whether salmon might have a similar experience.

And that (finally) leads us back to the humble bluntnose minnow. Around 1951, Hasler graduate students, Theodore Walker and Warren Wisby, began a series of experiments training bluntnose minnows to use their sense of smell to discriminate between different odors.

Warren Wilsby
Warren Wisby training bluntnose minnows to identify the water from different Wisconsin rivers and streams. Photo: Center for Limnology Archives

Walker trained his fish to differentiate between the smells of various species of aquatic plants, while Wisby began training his fish to identify water from two different streams near Madison – Otter and Honey Creeks. Fish were rewarded with food when they swan toward the odor of one stream and “discouraged” by a mild electric shock when they swam toward the other In a couple of months, Wisby had trained them to head toward water from the stream with the positive association of food.
Soon thereafter, Hasler conducted similar research on hatchery-raised salmon in Lake Michigan. In one study, he and his students “imprinted” young hatchery salmon with the smell of waters from tributaries of Lake Michigan. They then turned those fish loose in the lake and tracked them as they headed up those very same rivers and streams to spawn.
In the years that followed Hasler published his findings in journals and authored The Homing Salmon what’s now considered a classic article in Scientific American.
And, after 35 years or so of study, in which Hasler explained many other mysteries of salmon behavior – like their ability to navigate using the sun – we can thank the bluntnose minnow for being the “guinea pig” that got it all started!
Art Hasler hoisting a salmon near Lake Michigan. Photo: Center for Limnology archives.
Art Hasler hoisting a salmon near Lake Michigan. Photo: Center for Limnology archives.

 

2 thoughts on “Art Hasler, Bluntnose Minnows and How Salmon Get Back Home”

  1. In the 21st century, due to the molecular biology revolution and the progress in sensory neurobiology, we know that odorant receptors play an important role in homing. Both vomeronasal and olfactory receptors are the relevant sensory organs involved.
    The most amazing discriminatory homing mechanism to me is that used by King salmon migrating back to their birth place to spawn, in the Susitna River basin in Alaska. So many tributary streams, but widely divergent loci of return to the vast potential spawning grounds. Since these are glacial feeder streams to the Susitna, perhaps the ionic composition differences are responsible for this discriminatory behaviour?
    It would be nice to have a molecularly oriented update to Professor Hasler’s important research.

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