Fleming B Paul, Huffman David G, Bonner Timothy H, Brandt Thomas M
Department of Biology, Aquatic Station, Texas State University, 601 University Drive, San Marcos, Texas 78666, USA.
J Aquat Anim Health. 2011 Sep;23(3):117-24. doi: 10.1080/08997659.2011.616840.
We examined the gills of wild fish collected from central Texas for Centrocestus formosanus metacercariae to determine whether this temperature-restricted parasite had invaded the thermally dynamic Guadalupe River via an introduced population in its thermally stable tributary, the Comal River. We collected fish from three sites in the Guadalupe River near its confluence with the Comal River (upstream, at, and downstream) and one site in the Comal River. Centrocestus formosanus infected 14 of the 25 species examined (56.0%) and 171 of the individual fish (27.1%). Several of the infected fish represent new host records for the parasite, and two are listed as species of special concern by the state of Texas. Mean metacercarial intensities varied from 8 to 616 among species, and the highest recorded intensity was greater than 800 in two Guadalupe roundnose minnow Dionda nigrotaeniata. Among the 24 species examined from the Guadalupe River, 11 (45.8%) were infected with C. formosanus. Thorough surveys at the study sites yielded no living specimens of the first obligate intermediate snail host (red-rim melania Melanoides tuberculatus), which must be present to perpetuate the parasite. Thus, the infections were probably due to drifting cercariae that had been shed into the water column upstream of the study area in the Comal River. We therefore investigated spatial patterns in cercarial acquisition using caged fish to determine whether drifting cercariae were present in the water column at the study sites. Of 57 uninfected blacktail shiners Cyprinella venusta exposed to Guadalupe River water downstream from and at the confluence, 52 (91.2%) became infected with C. Formosanus metacercariae at a mean rate of 4 metacercariae/d. This finding extends the known geographic range of this invasive exotic parasite and is the first report of the life cycle being advanced in the fish assemblage of a thermally variable temperate stream in the USA.
我们检查了从得克萨斯州中部采集的野生鱼类的鳃，以寻找台湾棘带吸虫的后尾蚴，从而确定这种受温度限制的寄生虫是否通过其热稳定支流科马尔河中引入的种群，侵入了热动态变化的瓜达卢佩河。我们在瓜达卢佩河与科马尔河交汇处附近的三个地点（上游、交汇处和下游）以及科马尔河的一个地点采集了鱼类。在所检查的25个物种中，有14个（56.0%）感染了台湾棘带吸虫，171条个体鱼（27.1%）被感染。一些被感染的鱼类代表了该寄生虫的新宿主记录，其中两种被得克萨斯州列为特别关注的物种。不同物种间后尾蚴的平均感染强度从8到616不等，在两条瓜达卢佩圆吻米诺鱼（Dionda nigrotaeniata）中记录到的最高感染强度超过了800。在从瓜达卢佩河检查的24个物种中，有11个（45.8%）感染了台湾棘带吸虫。在研究地点进行的全面调查未发现第一种专性中间螺宿主（红边黑螺Melanoides tuberculatus）活体标本，而该宿主的存在是寄生虫得以延续的必要条件。因此，这些感染可能是由于在科马尔河研究区域上游释放到水柱中的尾蚴漂流所致。因此，我们使用网箱鱼研究了尾蚴感染的空间模式，以确定研究地点的水柱中是否存在漂流的尾蚴。在下游和交汇处接触瓜达卢佩河水的57条未感染的黑尾亮鲃（Cyprinella venusta）中，有52条（91.2%）感染了台湾棘带吸虫后尾蚴，平均感染率为4个后尾蚴/天。这一发现扩展了这种入侵外来寄生虫已知的地理范围，并且是该寄生虫在美国温度变化的温带溪流鱼类群落中完成生命周期的首次报道。
