Biologists hunting for North America’s largest freshwater crayfish have crowned a Tennessee bottlebrush crayfish measuring 86.6 millimeters as the continent’s record-holder, according to findings published in the journal Ecology. The discovery establishes a baseline size threshold for the region’s aquatic crustaceans and points to physiological limits rather than environmental factors as the primary cap on their growth.
The Search for North America’s Largest Crayfish
The collaborative project began after Caitlin Bloomer, a teaching assistant professor in the Department of Natural Resources and Environmental Sciences at the University of Illinois Urbana-Champaign, pulled a large specimen known locally as “Crawzilla” from Kentucky waters during a bio-survey. Convinced she had caught a record-breaking animal, Bloomer brought the crayfish back to campus to show colleagues, sparking a friendly rivalry.
To settle the debate, Bloomer enlisted museum curators and biologists nationwide to inventory their collections. Armed with precise measuring calipers, the research team identified 20 individuals across 18 species that exceeded typical dimensions. While Bloomer’s specimen secured a spot in the top 20 and stood out as the only burrowing crayfish on the list, the crown went to a Tennessee bottlebrush crayfish housed in the West Liberty University Astacology Collection in West Virginia.
Record-Holders and Institutional Collections
According to Zackary Graham, an assistant professor of biology at West Liberty University, the winning specimen was collected in 2011 by Dr. Zac Loughman and university students. Its carapace matches the length of a credit card, while its full span with claws and tail extends nearly the width of a notebook sheet. Both that record-holder and a second massive specimen are housed at West Liberty University.
The Illinois Natural History Survey, part of the Prairie Research Institute at the University of Illinois, claimed six spots among the top 20. Meanwhile, the Smithsonian Institution’s National Museum of Natural History contributed four specimens to the elite list.
Investigating Growth Limits in Freshwater Crustaceans
The inventory provided researchers with some of the first upper size thresholds for North American crayfish, which consistently maxed out around the 80-millimeter mark. This ceiling prompted the team to analyze potential environmental drivers of body size, including latitude, oxygen availability, and specific habitat types.
However, the analysis revealed no clear correlations between environmental conditions and body size. Because massive crayfish species thrive in other parts of the world, the absence of an environmental pattern led researchers to hypothesize that North American species are constrained by internal physiology. Bloomer noted that future research will examine whether the composition of their exoskeletons or specific muscular traits dictate their maximum dimensions.
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