This post is a great example of why I love the Internet. It starts out with an observation I've made several times over the past 10 years or so while bass fishing, that being the prevalence in some waters for bass to have very small leeches attached inside their mouths. Cool thing I noticed, but never thought much more about it. Then recently I stumble upon this piece of research and the lightbulb goes off - this is what I've been seeing.
Faisal M, Schulz C, Eissa A, Whelan G.
Widespread mouth ulcerations were observed in largemouth bass collected from eight inland lakes in the Lower Peninsula of Michigan during the summer months of 2002 and 2003. These ulcerations were associated with, and most likely caused by, leech parasitism. Through the use of morphological dichotomous keys, it was determined that all leeches collected are of one species: Myzobdella lugubris. Among the eight lakes examined, Lake Orion and Devils Lake had the highest prevalence of leech parasitism (34% and 29%, respectively) and mouth ulcerations (53% and 68%, respectively). Statistical analyses demonstrated that leech and ulcer prevalence varied significantly from one lake to the other. Additionally, it was determined that the relationship between the prevalence of ulcers and the prevalence of leech attachment is significant, indicating that leech parasitism is most likely the cause of ulceration. The ulcers exhibited deep hemorrhagic centers and raised irregular edges. Affected areas lost their epithelial lining and submucosa, with masses of bacteria colonizing the damaged tissues. Since largemouth bass is a popular global sportfish and critical to the food web of inland lakes, there are concerns that the presence of leeches, damaged buccal mucosa, and general unsightliness may negatively affect this important sportfishery.
Then, of course, finding one study leads to a list of references and more searching, and I find another paper;
which backs the first one nicely, actually coming out much earlier and from the east coast, and assures me this is what I've been noticing. The cycle continues as I now learn that this particular leech is highly present in the freshwater fishes of Lake St. Clair;
and most recently, this leech was found to be able to harbor the disease Viral Hemorrhagic Septicemia virus (VHSV) and is highly likely the/a vector for the transmission of this fish killer;
which brings this story full circle for me, as this disease and the subsequent federal ban on transportation of game fish from and between Great Lakes states several years back was the reason we didn't get our local lake stocked that year with fish from a hatchery in Wisconsin that I had ordered. It really is a small world after all...
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