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Fat threeridge

Amblema neislerii

Listing Status

  • Federal Status: Endangered
  • FL Status: Federally-designated Endangered
  • FNAI Ranks: G1/S1 (Critically Imperiled)
  • IUCN Status: CR (Critically Endangered)


The fat threeridge is a midsized freshwater mussel that can reach a length of four inches (10.2 centimeters). This species has an outer shell color of dark brown to black with seven to nine horizontal ridges, and an inner shell color range of bluish-white to light purple. The fat threeridge has two equal-sized teeth in the left valve and a larger and smaller tooth in the right valve (Florida Areas Inventory 2001, University of Georgia 2008).


Life History:

The fat threeridge is a filter feeder – filters food out of water. Their diet primarily consists of plankton and detritus (dead organic matter).

Little is known about the life history of the fat threeridge. It is believed that males release sperm in the water and the females receive the sperm through a siphon. Eggs are fertilized in the female’s shell and the glochidia (larvae) release into the water. The larvae attach to the gills or fins of a host fish to develop. The preferred host fish are different types of minnows and different species in the sunfish family (University of Georgia 2008). When the larvae metamorphose into juvenile mussels, they release from the fish and settle in their primary habitat.


Habitat and Distribution:

fat three ridge map

The fat threeridge inhabits slow to moderate current rivers with sand, gravel, and rocky rubble floors. This species can be found in the Apalachicola River and the lower Chipola River in northwest Florida (Florida Natural Areas Inventory 2001).


Freshwater mussels face a host of threats due to an increased human population and development. The main threat is the impoundment of fresh waterways. Waterways are impounded for many reasons including for fresh water supply, flood control, and hydropower. Impounding waterways causes the water current’s velocity to decrease causing sediment to build up in the river and covering the mussels located in the substrate (surface of habitat). Impoundments also cause habitat fragmentation, separating mussel populations and also individual mussels from algae and host fish (U.S. Fish & Wildlife Service 2006). River dredging also threatens to destroy freshwater mussel populations on the river floors. The Asian clam (Corbicula fluminea), an invasive species, can out-compete the fat threeridge for resources in its habitat (Florida Natural Areas Inventory 2001). Pesticide and chemical pollution poses a significant threat to mussels, since they are filter feeders and may ingest chemicals directly from their habitat.


Conservation and Management:

The fat threeridge is protected as an Endangered species by the Federal Endangered Species Act and as a Federally-designated Endangered species by Florida’s Endangered and Threatened Species Rule.  It is one of the target species in a 7-species Federal Recovery Plan.  Specific actions needed to recover the species include (USFWS 2003):

  • Secure extant subpopulations and currently occupied habitats and ensure subpopulation viability.
  • Search for additional subpopulations of the species and suitable habitat.
  • Determine through research and propagation technology the feasibility of augmenting extant subpopulations and reintroducing or reestablishing the species into historical habitat.
  • Develop and implement a program to evaluate efforts and monitor subpopulation levels and habitat conditions of existing subpopulations, as well as newly discovered, reintroduced, or expanding subpopulations.
  • Develop and utilize a public outreach and environmental education program.
  • Assess the overall success of the recovery program and recommend actions.



Florida Natural Areas Inventory.  2001.  Field guide to the rare animals of Florida.    

University of Georgia. (2008). Fat Threeridge Amblema neislerii. Retrieved July 11, 2011, from   Museum of Natural History:

U.S. Fish and Wildlife Service.  2003.  Recovery Plan for Endangered Fat Three ridge (Amblema neislerii), Shinyrayed Pocketbook (Lampsilis subangulata), Gulf Moccasinshell  (Medionidus penicillatus), Ochlockonee Moccasinshell (Medionidus simpsonianus), and    Oval Pigtoe (Pleurobema pyriforme): and Threatened Chipola Slabshell (Elliptio        chipolaensis), and Purple Bankclimber (Elliptoideus sloatianus).  Atlanta, Georgia.  142     pp.

U.S. Fish & Wildlife Service. (2006, June 8). Current Threats. Retrieved July 7, 2011, from Freshwater Mussels :


Image Credit FWC