Leino, R.L. and J.H. McCormick, 1997.  Histological Evidence for Repeat Spawning of Ruffe from the St. Louis River Estuary on Western Lake Superior, University of Minnesota-Duluth, U.S. Environmental Protection Agency

Histological Evidence for Repeat Spawning of Ruffe from the St. Louis River Estuary on Western Lake Superior

Abstract
Ruffe, Gymnocephalus cernuus, have experienced phenomenal reproductive success after their introduction into the Duluth-Superior harbor - St. Louis River estuary in the mid 1980's. They are now the most numerous trawl-caught fish in the harbor and are extending their range to other parts of Lake Superior and beyond. An important component of this striking population increase appears to be related to the ruffe's manner of spawning. In a typical year, 1994, spawning commenced within a week or two of ice-out and extended over the following 8 weeks. Histological observations revealed that females of different age groups spawned somewhat in succession, with older fish ovulating first. As the season progressed, earlier spawners were capable of repeat spawning, probably two or three times before the end of the spawning period. These observations suggest that the unstable spring weather characteristic of this region has a minimal effect on the success of a new ruffe year class. This is in contrast with several native species that spawn only once per year, and that consequently may suffer year class failures during post-spawning cold spells (at this latitude, year class strength can be reduced significantly by low water temperatures during the post-spawning period). Studies of ruffe ovarian histology also revealed that in 1994 most spawning involved age 3+ females. Most age 2 females resorbed their oocytes which were nearly mature. This suggests that with different conditions, e.g., shorter winters or less density-dependent growth inhibition, large numbers of age 2 ruffe could contribute to the exceptional reproductive success of this species. Strong age 2 contributions to spawning may have occurred in the Duluth-Superior harbor in other years and would be likely to occur more often in warmer parts of the Great Lakes.

Contact: Richard L. Leino, Department of Anatomy and Cell Biology, School Of Medicine, University of Minnesota, Duluth, MN 55812 or rleino@d.umn.edu
Keywords: Ruffe, Basic_biology, Environmental_impacts
Product Type: Publication, Proceedings, Impact
User Type: General