Documentation of giant floater (Pyganodon grandis) glochidia attached to larval lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes

Native freshwater mussels (family Unionidae) are in decline globally, including in the Laurentian Great Lakes. Glochidia, the parasitic larvae of unionid mussels, typically attach to sub-adult and adult fishes. Attachment of glochidia to larval fishes is more rare, and a lack of documentation exists on glochidial attachment on fish in the Great Lakes in general. We document the attachment of four glochidia to three larval lake whitefish (Coregonus clupeaformis) in shallow waters of Lake Superior, and we genetically identified the glochidia as giant floater (Pyganodon grandis). We only observed glochidia at 3% of all sites sampled on ∼0.02% of all fish (∼15,000) collected across lakes Superior, Michigan, and Huron. Although glochidial encystment on larval lake whitefish may be rare, it may also be difficult to detect with conventional sampling methods. Regardless, the association could have important implications for the ecology and conservation of both unionids and coregonines in the ever-changing Great Lakes.