Understanding complex reproductive ecology in fishes: The importance of individual and population-scale information

Many riverine cyprinids native to the Great Plains of North America are members of a reproductive guild that broadcast spawns pelagic, semi-buoyant ova. The task of fully understanding and appreciating the complexity of the reproductive ecology of this guild has been difficult. Although various efforts to understand their reproductive ecology have been conducted over the last 60 years, the results of these studies and the conclusions drawn from them have been inconsistent and oftentimes seemingly contradictory. The result has been varied and ill-informed conservation and management strategies based on an incomplete understanding of the reproductive ecology of these fish. We used gonadosomatic index, oocyte development, oocyte size distribution, and histological techniques to assess the reproductive ecology of sharpnose shiner Notropis oxyrhynchus in the upper Brazos River, Texas, between April 2003 and March 2005. Histological analyses of ovarian tissue revealed that reproduction occurred over a six-month period between April and September during which individual fish spawned multiple times. Patterns in gonadosomatic index, oocyte development, and oocyte size distribution indicated that sharpnose shiner spawn asynchronously except during periods of increased streamflow when spawning is synchronized within populations. Reproductive ecology of the sharpnose shiner reported in this study appears to be nearly identical to that recently reported for two other broadcast spawning cyprinids in the Great Plains, indicating that a more complete and consistent understanding of their reproductive ecology is beginning to emerge. We attribute this to the inclusion of both individual and population-scale analyses used in the most recent studies.