How Freshwater Clams Feed

Filter Feeding in Freshwater Bivalves

Freshwater clams (unionid mussels, sphaeriids) are filter feeders. They do not hunt; they strain microscopic particles from water.

Anatomy of Feeding

• Inhalant siphon draws water into the mantle cavity.
• Gills (ctenidia) trap particles (algae, bacteria, detritus, plankton) in mucus.
• Cilia move mucus-food strings to the mouth.
• Exhalant siphon expels filtered water and pseudofeces (rejected particles).

Diet

Phytoplankton, bacteria, organic detritus, dissolved organic matter. They also inadvertently filter silt and sand.

Factors Affecting Feeding Rate

• Clam size (larger = more filtration)
• Water current (faster flow = more particles encountered)
• Food concentration (seasonal, location-dependent)
• Temperature (metabolic rate)

Habitat Needs

Clean, well-oxygenated water with moderate flow and stable substrate. Pollution, sedimentation, and flow alteration threaten populations.