Specimens of the river shiner were collected from three locations in Pool 4 of the upper Mississippi River in Wisconsin and Minnesota during June, July, and August 1995. All individuals from the first collection (21 June) displayed early maturing, late maturing or mature ovaries, indicating that spawning commenced prior to this date. Ovarian cycling continued over the next seven weeks but ended by 18 August, when 100% of the individuals were atretic. Clutch sizes varied from 436 to 2754 ova in mature females that ranged from 48.3 to 87.9 mm standard length (SL). Clutch size was significantly dependent on SL, but slopes and intercepts declined significantly over time. Mean clutch size declined significantly from 1600 on 30 June to 1056 and 1010 on 8 July and 11 August, respectively. This decline remained significant after means were adjusted for fish size. Mean mature oocyte size remained constant (0.89 mm) during the same period and was not dependent on standard length. Ovulated ripe oocytes in two fish ranged from 1.06 to 1.22 mm. The overall ovarian cycling schedule supported the hypothesis that the river shiner is a multiple clutch spawner in the upper Mississippi River.
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ACKNOWLEDGEMENTS We thank Becky Maxson, Mark Stopyro, Konrad Schmidt, Roland Sigurdson, and Dick Reynolds for assisting with collections. We thank Jack Enblom for his generous loan of equipment. A special thanks to Richard Baker and Jack Wingate for their long-term support of nongame fish research. This research was funded in part by the Minnesota Department of Natural Resources Natural Heritage and Nongame Research Program and by the Undergraduate Research Opportunities Program, University of Minnesota.