Lampreys of the St. Joseph River Drainage in Northern Indiana, with an Emphasis on the Chestnut Lamprey (Ichthyomyzon Castaneus)

Abstract

This study was initiated in response to concern about parasitism by lampreys on trout in the
Little Elkhart River of the St. Joseph River drainage in northern Indiana. Identification of 229 lampreys
collected in the St. Joseph River drainage during 1998–2012 revealed 52 American brook lampreys
(Lethenteron appendix), one northern brook lamprey (Ichthyomyzon fossor), 130 adult chestnut lampreys
(I. castaneus), five possible adult silver lampreys (I. unicuspis), and 41 Ichthyomyzon ammocoetes. The
brook lampreys are non-parasitic and do not feed as adults, so most if not all parasitism on fish in this
system is due to chestnut lampreys. Electrofishing surveys in the Little Elkhart River in August 2013
indicated that attached chestnut lampreys and lamprey marks were most common on the larger fishes
[trout (Salmonidae), suckers (Catostomidae), and carp (Cyprinidae)] at each of three sites. This is consistent
with the known tendency for parasitic lampreys to select larger hosts. Trout in the Little Elkhart River
may be more vulnerable to chestnut lamprey attacks because they are relatively large compared to
alternative hosts such as suckers. Plots of chestnut lamprey total length versus date of capture revealed
substantial variability on any given date. This may be due to variability among individual streams and
individual years and may also result from variability among individual lampreys in when they initiate and
terminate parasitic feeding.