Reproductive ecology of red shiner Cyprinella lutrensis in the Brazos River, Texas
Knabe, Douglas W.
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I studied the reproductive ecology of red shiner Cyprinella lutrensis at four sites on the upper Brazos River, Texas from January 2008 through December 2009. Using gonadosomatic indices, vitellogenic oocyte diameter, and histological analyses, I found that red shiner exhibited a protracted spawning season lasting from April through August. Spawning occurred continuously throughout the spawning season with two apparent primary times of reproductive activity. While the relationship between reproduction and discharge was not statistically significant, there was some evidence that high stream discharge may delay the onset of reproductive activity. I did not find evidence of any mass-synchronized spawning event within the population in relation to discharge throughout the year; rather red shiner exhibited a gradual peak in reproductive activity twice during the reproductive season. Histological analyses indicated that individual red shiners spawned on a daily basis throughout the spring and summer regardless of discharge levels. This spawning typology is in sharp contrast to that of many other cyprinids found in the upper Brazos River, such as plains minnow Hybognathus placitus, smalleye shiner Notropis buccula, sharpnose shiner Notropis oxyrhynchus, which are known to be broadcast spawning fishes that spawn asyncronously throughout the reproductive season, as well as synchronously in response to flood events or increased base flow. The ability of red shiner to spawn under a wide range of streamflow conditions likely plays a large role in its ability to persist in the highly variable habitat of the upper Brazos River and other Great Plains streams. This reproductive strategy is also likely an important factor in the ability of red shiner to easily become established in systems where it is nonnative and hybridize with many congeners including blacktail shiner Cyprinella venusta and spotfin shiner Cyprinella spiloptera.