Species Replacement in a Reservoir Fish Community: Silverside Feeding Mechanics and Competition

Abstract

The brook silverside (Labidesthes sicculus) was the only atherinid species found in Lake Texorna, Oklahoma, from 1944 to 1953. Inland silversides (Menidia beryllina) were first collected in Lake Texoma in 1953 and had completely replaced Labidesthes by 1955. We conducted comparative studies of feeding mechanics and feeding efficiencies of Labidesthes and Menidia to see if there was a competitive differential between species that could have been a factor in the replacement of Labidesthes by Menidia. Menidia has a protrusible and tube-shaped mouth that is more successful capturing evasive copepod prey than the v-notched mouth of Labidesthes. While both species have similar feeding rates for slow-swimming daphnids, Menidia has higher feeding rates than Labidesthes for cyclopoid and calanoid copepods. Menidia's use of copepod prey is a competitive advantage over Labidesthes in laboratory competition experiments. We hypothesize the same advantage was an important factor in displacing Labidesthes from Lake Texoma.Key words: planktivory, Labidesthes sicculus, Menidia beryllina, Lake Texoma