The Smell of Fear: Ruffe “Alarm” Pheromones
It’s lunch time in Peter Sorensen’s laboratory at the University of Minnesota. Goldfish gobble flakes and trout go wild for their pellets while fathead minnows gulp brine shrimp. However, the finicky Eurasian ruffe, an exotic fish from the Duluth-Superior Harbor, are kept primed for their tests and mazes on a diet of hotdogs. Sorensen’s staff had problems getting ruffe to eat anything but worms. They also had a hard time raising and buying enough worms to keep the ruffe alive, so they came up with this tubular alternative. Hotdogs are hardly brain food but, judging from peripheral research results, at least they smell appetizing to ruffe.
Like most freshwater fish, Eurasian ruffe have a keen sense of smell. Sorensen, a pioneer of fish pheromone research, and his colleagues in the Department of Fisheries and Wildlife understand that smells can often be powerfully attractive or repulsive. They are attempting to harness the capacity of pheromones to help manage fish populations.
“Pheromones are chemical signals that pass between members of the same species that evoke potent, instinctual responses,” said Sorensen. “Pheromones are environmentally-benign, highly-specific, and conceivably an inexpensive way to manage populations of nuisance fish.”
Map of Confirmed Ruffe Sightings in Lake Superior
During an investigation of attractant (sex) pheromones, Sorensen and his colleagues switched tactics and discovered that Eurasian ruffe repel other ruffe with an offensive odor, an alarm pheromone, that seeps from their injured skin. “Damaged ruffe skin emits an extremely repugnant odor that suppresses the swimming and feeding activities of exposed ruffe,” said Sorensen. “Ruffe respond almost immediately and very dramatically to this alarm pheromone and, when possible, avoid it. Clearly, this cue has potential for managing ruffe. The key remaining question is how effective it will be in the large open spaces of the lake,” he said.
Pheromones aren’t just “smells.” They are probably the most ancient form of animal communication. “Fish commonly use pheromone cues to navigate and coordinate intraspecific activities in waters that are often turbid, vast, and relatively featureless,” said Sorensen. Pheromones are already common for controlling insects. Generally, insect pheromones are species-specific and the same seems true of fish pheromones. In Sorensen’s study, ruffe did not respond to the alarm pheromones of injured yellow perch (a member of the same subfamily as ruffe) nor did goldfish respond to injured ruffe.
Although organisms can lose their sensitivity to a stimulus after long-term exposure, Sorensen doesn’t believe wild Eurasian ruffe would normally become desensitized to their alarm pheromone; the Great Lakes are so huge and the initial response of the fish is to swim away. “There is no obvious reason why they would continue to expose themselves to it.”
The perch-like Eurasian ruffe became part of the fauna in the Duluth-Superior Harbor in the early 1980’s. Presumably, they crossed the Atlantic Ocean as accidental passengers in the ballast tanks of cargo ships. Within a decade of their detection, Eurasian ruffe became the most abundant fish trawled from the bottom of the harbor.
Currently, ruffe have spread along Lake Superior’s south shore to the Fire Steel River, east of Ontonagan, MI; to several harbors along the north shore to Thunder Bay, Ontario; and to Alpena, MI, on Lake Huron. Attempts to control the expanding population of ruffe with predators and piscicides (chemicals that kill fish) have failed and alternatives are being sought.
Managing invasive fish species with their own non-toxic pheromones is a new and attractive idea. Authorities in Alpena have approached Sorensen about using the alarm pheromone to exclude ruffe from areas where they are not wanted, such as docks where ships take on ballast water. Sorensen and his coworkers also characterized a ruffe sexual attractant that might be used in conjunction with the alarm pheromone.
Sorensen’s results were published in the Journal of Great Lakes Research. To find out more, you can order a reprint of the article, Injured Eurasian Ruffe, Gymnocephalus cernuus, Release an Alarm Pheromone that Could be Used to Control their Dispersal, from Sea Grant (JR 462 on the journal reprint order form).
By Sharon Moen