U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3103 

September 2005

Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin

Host Fish Identification and Early Life Thermal Requirements 

for the Federal Endangered Winged Mapleleaf Mussel

Printed on recycled paper

The winged mapleleaf mussel (Quadrula fragosa, WML) is a 

Federal endangered species historically inhabiting at least 34 

river systems in 12 Midwestern states. Only four populations are 

currently known to exist, including one confirmed reproducing 

population in the St. Croix National Scenic Riverway (NSR) 

bordering Minnesota and Wisconsin. Recovery efforts are 

limited by a lack of life history information, particularly which 

species of fish serve as host to the mussel’s parasitic larvae 

(glochidia).

Since 1997, biologists at the University of Minnesota have tried 

to identify host fish for the WML. Department of the Interior 

colleagues working in western Wisconsin at the U.S. Fish and 

Wildlife Service’s La Crosse Fishery Resources Office and 

Genoa National Fish Hatchery, the National Park Service’s St. 

Croix NSR, and the U.S. Geological Survey’s Upper Midwest 

Environmental Sciences Center (UMESC) in La Crosse joined 

the team in 2001 to expand and accelerate the laboratory host 

fish identification program by making use of the well-equipped 

aquatic research facilities at UMESC. We report on several 

WML early life history investigations conducted at UMESC 

since autumn 2003 to identify suitable host fish species and 

evaluate thermal requisites for the development of glochidia into 

free-living juvenile mussels.

A series of WML host-fish identification trials were conducted 

with as many as four species of the catfish family (Ictaluridae) 

including blue catfish (Ictalurus furcatus; BCF), channel catfish 

(I. punctatus; CCF), flathead catfish (Pylodictus olivarus; FHC), 

and slender madtom (Noturus exilis; SMT). On four dates in 

autumn 2003, fish were infested with viable glochidia from 

several winged mapleleaf mussels from the St. Croix River. 

One group of BCF and one group of CCF (5 fish/group) were 

infested each day by placing them in 2 L of vigorously aerated 

well water innoculated with about 150 ml of a glochidial slurry. 

Groups of SMT and FHC (2 fish/group) were infested by 

pipetting glochidia (5–15 mL) directly onto the gills.

Infested fish were then assigned to one of three water 

temperatures (Test I, II, or III): 

The only known reproducing population of winged mapleleaf mussels 

(Quadrula fragosa) inhabits the St. Croix National Scenic Riverway.

Fish were kept in laboratory aquaria during all tests to monitor the daily 

excystment of juvenile winged mapleleaf mussels (Quadrula fragosa).

Water siphoned from the aquaria each day was filtered through a 

series of sieves (53, 153, and 202 μm mesh). Materials retained 

on sieves were illuminated with cross-polarized light and 

examined with a dissection microscope to enumerate mussels. 

Juvenile mussels were considered viable if either external 

(foot, valve) or internal (ciliary) movement was observed. The 

consecutive 5-d period during each test when the maximum 

number of viable juveniles was recovered from an aquarium 

was considered the period of peak juvenile excystment.

About 11,600 viable juveniles were recovered within 7 weeks 

from groups of BCF and CCF held at a constant temperature of 

19.6°C (Test I). Production by BCF accounted for 95% of this 

total. Peak recovery from CCF and BCF occurred 4–5 weeks 

Test I – fish were maintained 49 d in aquaria that received a 

continuous flow of 19.6°C water; 

Test II – one group of CCF was maintained 45 d at 12.5°C, 

then acclimated and placed in aquaria that received a 

continuous flow of 19.5°C water; 

Test III – one group of CCF was maintained 45 d at 12.5°C, one group of CCF was maintained 45 d at 12.5°C, 

then held in a thermal regime similar to the St. Croix River 

from November 2003 to June 2004.
and 5–6 weeks after infestation, respectively. The 

rate at which glochidia successfully transformed 

into viable juveniles was 50% on BCF, but only 7% 

on CCF. Juveniles were not recovered from FHC or 

SMT. These results suggested that BCF is a suitable 

host whereas CCF was a marginal host. 

In Test II, about 9,300 viable juveniles were 

recovered from the CCF after 11 weeks of 

development in temperatures that ranged 11.8–

19.7°C (Test II). When compared to the results 

from Test I, this was a 64-fold increase in the 

mean number of juveniles produced per CCF. A 

combination of factors may explain this difference. 

First, the mean weight of CCF used in Test II (156 

g) was much greater than that of CCF (18 g) and 

BCF (60 g) used in Test I. This likely provided more 

gill surface area on which glochidia could encyst. 

Second, more glochidia were used to infest fish for 

Test II than for Test I. Overall, these results suggest 

record of the mean daily water temperature and the number of 

juveniles recovered daily from each aquarium during Tests I and 

II, we estimated the temperature threshold for development of 

CCF-encysted glochidia into juveniles to be 9.24°C.

The validity of this estimate was evaluated during Test III. Peak 

excystment began 21 June when WML attained an estimated 

453°C•d of development. Based on the results of Tests I and 

II, peak excystment during Test III was predicted to start 14 

June when 395°C•d of development was attained. Thus, we 

successfully predicted the dates of peak excystment to within 1 

week during a 37-week developmental period, representing an 

error rate of < 3%. As the predicted dates of peak excystment 

came and passed, few juveniles were recovered at cold test 

temperatures (<15°C), but warmer temperatures (17–20°C) later 

appeared to act as a thermal cue and initiate excystment. This 

test was repeated the following year (September 2004 – June 

2005) when peak excystment was predicted to begin 11 June but 

actually began 9 June, representing an error rate of < 1%. This 

test also provided supporting evidence for the 17–20°C thermal 

cue that we speculate is needed to trigger excystment.

These results confirm the validity of our approach to quantify 

the period of thermal development necessary for transformation 

of WML glochidia into juveniles on CCF and present a model 

to quantify temperature dependent development for other 

mussel species. This information will aid recovery teams in 

establishing successful propagation programs for mussels with 

historically wide-ranging distributions and multiple hosts (such 

as the WML) and can be used to improve juvenile mussel 

production for other listed species with existing propagation 

programs.

A juvenile winged mapleleaf mussel (Quadrula fragosa; foot extended) 

recovered after 266 days of development in a simulated St. Croix River thermal 

regime and <24 hours after excystment from its channel catfish host (Ictalurus 

punctatus).

CCF is also a suitable host. This finding is useful to 

managers wanting to develop propagation strategies 

to recover WML populations throughout its historical range, 

including the St. Croix and other northern locations where CCF 

are often present year-round and BCF are usually absent or rare.

After fish were maintained in warm water (19.5°C) such as that 

used throughout Test I, peak recovery of juveniles from CCF 

during Test II occurred about one week earlier than it did during 

Test I. This finding suggested the physiological mechanisms 

responsible for transformation of glochidia into juveniles on 

CCF proceeded more slowly at colder temperatures.

A species-specific temperature threshold for early life 

development of poikilotherms can be empirically derived 

from repeated embryological observations made over an 

environmentally relevant temperature range. Given a complete 

Recovery of juvenile winged mapleleaf mussels (Quadrula fragosa) from channel catfish 

(Ictalurus punctatus) reared in a simulated St. Croix River thermal regime, September 2004–

June 2005.

For more information, contact

Mark Steingraeber

U.S. Fish and Wildlife Service, Fishery Resources Office

555 Lester Avenue, Onalaska, Wisconsin 

608.783.8436

or 

Teresa Newton

U.S. Geological Survey, Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road, La Crosse, Wisconsin

608.781.6217