Freshwater Mollusks Survive Fish Gut Passage

Randy J. Brown


Freshwater mollusks figure prominently in the diets of humpback whitefish (Coregonus pidschian) and broad whitefish (C. nasus), two benthic-feeding coregonid species. A recent examination of pea clams (Sphaeriidae), valve snails (Valvatidae), and pond snails (Lymnaeidae) from the lower digestive tracts of these fish found that many of the mollusks were alive. Survival completely through gut passage would indicate a dispersal mechanism for freshwater mollusks that has not been previously recognized. A field investigation was conducted with wild-caught humpback and broad whitefish to test the hypothesis that clams and snails are capable of surviving complete gut passage. Wild fish were captured alive and held in collection totes to obtain feces samples. Pea clams and valve snails were abundant in fish feces, and pond snails were present but not abundant. An average of 483 pea clams and 833 valve snails per fish were observed to have survived complete gut passage, while only a single surviving pond snail was found. These findings suggest that fish may play an important role in the dispersal of freshwater mollusks within freshwater systems.

Key words: Sphaeriidae, clams, Valvatidae, Lymnaeidae, snails, coregonid fish, gut passage

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