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US Fish & Wildlife Service FieldNotes

Genoa National Fish Hatchery mussel biologists dazzled by 50,000 juvenile winged mapleleaf mussels.

Region 3, December 8, 2016
Displaying winged mapleleaf (Quadrula fragosa)
Displaying winged mapleleaf (Quadrula fragosa) - Photo Credit: n/a
Juvenile winged mapleleaf in petri dish for counting (1,922 total)
Juvenile winged mapleleaf in petri dish for counting (1,922 total) - Photo Credit: n/a
Juvenile winged mapleleaf under microscope
Juvenile winged mapleleaf under microscope - Photo Credit: n/a

Each fall, hatchery biologists working with U.S. Park Service staff, MN DNR mussel biologists and staff from other U.S. Fish and Wildlife Service offices visit the St. Croix as many as 15 times looking for the federally endangered Winged Mapleleaf that thrive in the clean, clear water. Females holding mussel larvae are brought back to Genoa National Fish Hatchery, the larvae (glochidia) are allowed to attach to channel catfish and then the female mussels are returned to the St. Croix River. (displaying winged mapleleaf photo)

In the wild the larval mussels remain attached to the catfish until late spring when the water begins to warm. Hatchery staff have worked hard to replicate this experience for the catfish and their mussel riders in the lab, but it has proven to be challenging. In early November 2016 Genoa’s mussel biologists moved 38 channel catfish, just a small part of the 410 infested with winged mapleleaf more than a month before into an aquarium system where they are warmed up to replicate spring’s warming water temperatures. By the week of Thanksgiving the first juvenile winged mapleleaf of 2016 were collected.

The first vision of newly transformed juvenile mussels is more akin to stars in a very dark sky. Only by putting the dish on the microscope do the tiny moving spots take on the shell and foot characteristic of their adult counterparts. Juvenile mussels are counted on the microscope by estimating the number in each square of the dish. Some days this takes 10 minutes, other days it can take an hour. Every other day juveniles are collected and counted and moved from their dish into the system where they’ll eat and grow. Winged mapleleaf are a challenging species to culture and are especially delicate when young. Very few have been laboratory cultured to more than 0.5 mm.

Contact Info: Megan Bradley, (608) 689-2605, megan_bradley@fws.gov