The Chestnut Lamprey, Ichthyomyzon castaneus, is a Native Species commonly found in Lakes and Rivers throughout the Great Lakes region. They are considered to be an indicator species and their presence in a body of water has been closely associated with healthy clean water. There is, however, one negative component to their presence in a watershed and that is the negative impact they can have on fish populations during their parasitic phase.
The chestnut Lamprey has two primary life stages to complete its life cycle. The first life stage is the larval phase, commonly referred to as ammocoetes, in which the larval form is primarily a filter feeding organism. The larva will live in the fine and silty bottom sediments in slower backwater pools for an average of 5-7 years. When the larva reach 4-6 years of age they go through a metamorphosis and develop teeth and a sucking mouth disk characterized by the adult parasitic phase of their life cycle.
The metamorphic phase appears to take place from October through the end of January as the ammocoetes enter the second life stage as parasitic adults. As the water begins to warm up in April the larva exit their burrows and enter the parasitic feeding phase of their life cycle. The Chestnut Lamprey tends to be more active at night and during low light periods. Peak feeding periods for the adults range from May through July with some adults holding over until the following spring to spawn. The adult chestnut lamprey will continue to feed until the peak spawning season occurs from June to July. After spawning the adults will die and the cycle is repeated. (Hall, 1963)
In Michigan, most of our trout streams have an established population of Chestnut Lamprey, but, the Manistee River has been mentioned as having a highly abundant population in the upper portions of the watershed, especially from County Road 612 to Sharon Road. As the water temperature reaches 50 F degrees the adults begin to feed. (Hall, 1963) This temperature change coincides nicely with the obvious annual appearance of Chestnut Lamprey on the trout we catch throughout the first half of our trout season. Most of the trout in our streams will react to streamer patterns tied with a long and “leechy” appearance and lots of undulating movement in the materials.
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In late April to early May the Chestnut Lamprey larvae metamorphosis occurs and they become parasitic. To say our trout dislike them is an understatement. Here are a couple of color combos that I like for our streams using the HFGC format. Flymen micro shanks, Chocklett’s finesse chenille for fill, MFC buggerbou for tail and top, MFC Kreelex fish flash for accent, and Senyo’s Chromatic Brush for the head. There are 9 articulations and a weighted cone hidden in the head.
Matching the Hatch
Chestnut Lamprey will range in size from 4-5” early in their adult development and will attain lengths of +7” at maturity. It’s not a coincidence that as the lamprey continue to become more active that the streamer fishing becomes more consistent for us, especially on the Manistee River. The trout are not only actively feeding at this time, but they are also combating the presence of an “alien intruder” that will parasitize them if they let their guard down! It is not uncommon to see some pretty exciting visuals while fishing “leechy” patterns at this time of year. Some fish will recklessly chase them out of their territory and oftentimes will strike with violent takes.
Take this information for what it is worth, but having an understanding of the natural phenomenon that occurs during this time of the year can only help you. Fly selection, fly movement, and presentation are all critical components to angling success and having one more arrow in the quiver can only be a positive. The Chestnut Lamprey life cycle is really just an example of one more hatch that you should pay close attention to as we move closer to the opening day of trout season here in Michigan.
Hall, J. 1963. An ecological study of the chestnut lamprey, Ichthyomyzon castaneus, in the Manistee River, Michigan. Ann Arbor, MI: University of Michigan.