Luring Ruffe with Smell
New research shows promise for controlling Eurasian ruffe through their sense of smell. Photo courtesy of the U.S. Geological Survey
It's official: Eurasian ruffe (Gymnocephalus cernuus) have sex lives propelled in part by the odor of a female ruffe's urine. Odor is a logical way for these invasive fish to "hook up" since males and females look alike and spawn in murky waters. Unlike vividly hued fish from coral reefs, which rely more on their eyes for information, the drab ruffe depend on their noses and sensitive lateral lines.
Sea Grant-funded researchers at the University of Minnesota have shone the first light onto the reproductive hormones and pheromones of ruffe, opening a potential means of managing invasive populations using pheromonal attractants. Pheromones are chemical compounds produced by an animal that influence the behavior or development of other members of the same species.
After four years of laboratory investigation, Peter Sorensen, professor of fisheries, wildlife, and conservation biology, and his colleagues found that the urine of female ruffe approaching ovulation contains a pheromone, 20β-S, which influences the behavior of their male counterparts.
20β-S is shorthand for "4-pregnen-17,20β,21-triol-3-one", a steroid that stimulates egg production and helps trigger male passion. The discovery of how 20β-S affects reproduction may also apply to walleye and perch, close relatives of ruffe.
The study, published this October in General and Comparative Endocrinology, found that 20β-S surged through female ruffe just prior to ovulation and spawning and that the odor of pre-ovulatory females provoked three- to five-fold increases in male swimming activity and increased the amount of nudging (what might pass for kissing). Injecting female ruffe with 20β-S produced similar male responses.
"I've been studying pheromones for 20 years, and this one is unusual," said Sorensen. "It's different because itís related to a maturation-inducing steroid, it drives a behavioral response, and it operates prior to spawning. It is also the first time that the sex steroid 20β-S has been associated with pheromonal communication in fish. Likely it is associated with pre-spawning aggregation in this species."
Although the field of knowledge about ruffe pheromones is in its infancy, Sorensen's research is making critical steps that could advance fisheries management. In a January 2001 Seiche article concerning ruffe (The Smell of Fear: Ruffe "Alarm" Pheromones), Sorensen and his colleagues discovered an alarm pheromone that radiates from the skin of a wounded ruffe. Alarm pheromones scare off members of the same species. Sex pheromones do the opposite. Conceivably, ruffe could be managed in places like the Duluth Superior Harbor using combinations of pheromonal repellants and lures. The U.S. Geological Survey estimates 4.4 million ruffe spawned in the harbor last spring.
Sorensen is enthusiastic about the next step, should this line of research receive more funding. "It's like a needle in the haystack," said Sorensen. "We've determined that the needle exists and have a very good idea of what it looks like, but now we've got to locate it and make copies. Eventually, we might be able to apply it, thereby inventing new, non-toxic, species-specific ways to manage these invasive fishes in the Great Lakes."
Sorensen has also hunted for pheromones in goldfish, carp, and lamprey.
Reprints of the article, Evidence that 4-pregnen-17,20β,21-triol-3-one functions as a maturation-inducing hormone and pheromonal precursor in the percid fish, Gymnocephalus cernuus, are available free from Sea Grant. Look for JR 496 on the products order form, page 7 under the journal reprint category.
By Sharon Moen