Using pheromonal attractants to control Eurasian ruffe—a fish that hitchhiked to the Great Lakes in ship ballast water and now competes with native fish for food and habitat—is one step closer to reality thanks to research funded by Minnesota Sea Grant. Pheromones are chemical compounds animals produce that influence the behavior or development of other members of the same species.

Peter Sorensen, professor of fisheries, wildlife, and conservation biology at the University of Minnesota, and colleagues spent four years of laboratory investigation to find that the urine of female ruffe approaching ovulation contains a pheromone, 20b-S, that influences the behavior of male ruffe. 20b-S is shorthand for 4-pregnen-17,20b,21-triol-3-one, a steroid that stimulates egg production and helps trigger male passion. Although knowledge about ruffe pheromones is in its infancy, Sorenson hopes it will eventually lead to “new, nontoxic, species-specific ways to manage these invasive fishes in the Great Lakes.”

The study found that 20b-S surges through female ruffe just before they ovulate. The urine 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). Males responded similarly when female ruffe were injected with 20b-S. “I've been studying pheromones for 20 years, and this one is unusual,” said Sorensen. “It's different because it’s 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 20b-S has been associated with pheromonal communication in fish. Likely it is associated with pre-spawning aggregation in this species.”

Previously, Sorensen and colleagues discovered an alarm pheromone that radiates from the skin of wounded ruffe, scaring off members of the same species—the opposite effect of sex pheromones. In places like the Duluth Superior Harbor, where an estimated 4.4 million ruffe spawned last spring, they could conceivably be managed using combinations of pheromonal repellants and lures. Reprints of the study article, “Evidence that 4-pregnen-17,20b,21-triol-3-one functions as a maturation-inducing hormone and pheromonal precursor in the percid fish Gymnocephalus cernuus,” published this fall in General and Comparative Endocrinology, are available free by contacting Minnesota Sea Grant at seagr@d.umn.edu

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