An attempt to differentiate sympatricIchthyomyzonammocoetes using meristic, morphological, pigmentation, and gonad analyses

Abstract

We assessed characters that could be used to differentiate ammocoetes of chestnut lamprey ( Ichthyomyzon castaneus Girard, 1858), northern brook lamprey ( Ichthyomyzon fossor Reighard and Cummins, 1916), and silver lamprey ( Ichthyomyzon unicuspis Hubbs and Trautman, 1937). We sampled ammocoetes of the three species from 25 streams around the Great Lakes. Existing genetic markers were used to identify chestnut lamprey for this study, but the lack of genetic markers for silver and northern brook lampreys forced our preliminary classification of these two species to be based on stream-specific catch records of adults. Comparison of ammocoete gonads was inconclusive as a technique to distinguish between these two species. Other characters examined (including pigmentation patterns, morphometric characters, body shape, and myomere counts) varied significantly among species, but were inadequate for use as diagnostic characters because of high intraspecific variation and overlapping ranges. Chestnut lamprey ammocoetes were sometimes distinguishable by their pigmented lateral line organs, but this character was not always apparent. The lack of distinguishing characteristics makes existing taxonomic keys misleading for identifying Ichthyomyzon lamprey larvae.