Forage Fish Assemblages in the Brazos River Upstream and Downstream from Possum Kingdom Reservoir, Texas

The forage fish assemblage of the Brazos River was sampled at one location above and four locations below Possum Kingdom Reservoir each month for one year. A total of 13,936 individuals representing 18 species, 14 genera and five families were collected. Five of these species, Notropis stramineus, Notropis atherinoides, Hybognathus placitus, Hybopsis aestivalis and Cyprinodon rubrofluviatilis were found only upstream from Possum Kingdom Reservoir. Hybognatus placitus accounted for 45% of fish captured at the upstream site. In contrast, nine species were collected exclusively in the tailwaters, including Etheostoma spectabile, Percina sciera, Campostoma anomalum, Notropis venustus, Pimephales notatus, Labidesthes sicculus and Fundulus notatus. Only four species were obtained at all five stations—Gambusia affinis, Menidia beryllina, Pimephales vigilax and Notropis lutrensis. N. lutrensis was the most common tailwater species equalling 87.9% of the total downstream catch. Median species diversity indices ranged from 0.129 to 0.451 for the five stations, with the highest value at the upstream station. Coefficients of biotic similarity ranged from 0.20 to 0.62, with the upstream station clearly being the most dissimilar. These findings are discussed relative to environmental effects of hypolimnetic release of reservoir waters.