Exotic Armored Catfishes in Texas: Reproductive Biology, and Effects of Foraging on Egg Survival of Native Fishes (Etheostoma fonticola, Endangered and Dionda diaboli, Threatened)
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Armored catfishes (Loricariidae), native to Central and South America, were introduced into North American waters through the aquarium trade, and became established in Texas waters in 1964. There has been concern that breeding populations of these exotics could affect native species through dietary overlap, egg predation, and other factors. This study focused on two related topics: 1. the reproductive biology of Hypostomus in the San Marcos River, Texas; and 2. the potential effect of the foraging activities of the exotic on the egg survival of two native central Texas fishes (the endangered fountain darter, Etheostoma fonticola, and the threatened Devils River minnow, Dionda diaboli). Based on the oocyte diameters and estimated mean fecundity (2,109) of the exotics, the Hypostomus population in the San Marcos River is reproducing as well in their new habitats as could be expected, and is not yet suffering from the effects of crowding. Photoperiod was the only environmental influence that could be associated with a peak in spawning activity, which occurred during the months of March through September. Size-frequency distribution plots of oocyte diameters from Ripe ovaries revealed two distinct modal diameters, suggesting a modified group-synchronous mode of ovarian development. Potentially deleterious effects of Hypostomus foraging on Devils River minnow and fountain darter eggs were assessed experimentally to evaluate the threat to these native species. The survival rate for fountain darter eggs was substantially lower when exposed to foraging Hypostomus, and three whole eggs were found in the digestive tract of the two experimental Hypostomus. These findings suggest that the exotic is positively trophotaxic toward fountain darter eggs, and may substantially reduce the breeding success of the darter in shared habitats. In contrast, egg survival rates for the Devils River minnow were only slightly lowered by foraging Hypostomus, and no eggs were recovered from the digestive tracts of the experimental Hypostomus.