Changes in the Trematode Fauna of Clams in the Little Brazos River, Texas

Abstract

Before the 1950-56 drought, six (possibly seven) species of trematodes were found in the Little Brazos River clams. Seven years after the drought the clams were found to contain two species of flukes found previously and one species not previously found. The range of Aspidogaster conchicola von Baer, 1826, and Cotylaspis insignis Leidy, 1857, is extended to include Texas. The Little Brazos River is a small, shallow tributary of the Brazos River. Before the drought of 1950-56, nine species of clams were found in the river, some in great numbers. Sporadic collections of Little Brazos mollusks have been made by students for various research projects since 1935, and trematodes representing six, and possibly seven, species in five families have been found in clams. Five previously named species were identified, and an additional genus was represented by either one or two unnamed species. During the drought the river ceased to flow; many isolated pools were formed and later became stagnant. In the summer and autumn of 1956 a fairly intensive search failed to reveal any living clams. The Little Brazos River rose and overflowed its banks in the spring of 1957 and has since continued to flow. Several species of clams now live in the river but not in their former abundance. A study was undertaken from February to May 1964, to determine the effect of the drought on the trematode fauna in the clams. MATERIALS AND METHODS One hundred and ninety-seven clams of nine species were collected before the drought, while 90 clams of seven species were collected 7 years after the drought ended. In both instances the clams were collected by hand or scoops from approximately a mile and a half of the Little Brazos River in Brazos County, Texas. Since the river became dry in many places during the drought, clams were collected from several different pools of the river to increase the probability of obtaining a representative sample. The viscera, foot, and mantle of the clams were examined under a dissecting microscope for larval and adult trematodes. Cysts of metacercariae were broken with needles or by gently applying pressure Received for publication 6 December 1965. on a cover slip. The larval flukes were pipetted onto a slide and stained by adding a small amount of neutral red.