[Particulate Matters]

filtering mechanism laboratory


Oysters are filter-feeders, drawing water in over its gills through the beating of cilia. Suspended food (plankton) and particles are trapped in the mucus of the gills and transported to the mouth, where they will be eaten, digested and expelled as feces or psuedofeces. Feeding activity is greatest in oysters when water temperatures are above 50°F (~10°C).

The procedure for performing a live filtering experiment is simple and requires only a few pieces of equipment. Viewing this experiment is best accomplished with a stereoscope to get the full effect of the movement and transport of particulate matter by the oyster. Follow the procedure and you will be able to see how an oyster is able to filter materials from the environment and selectively process them as food or pseudofeces.

[oyster gill]
A longitudinal view into a live oyster showing the gills and tentacles of the mantle.


  • live oysters (as many as you need; fresh if possible)
  • shucking knife
  • saltwater or artificial seawater (14-21 ppt)
  • microscopes (stereo or dissecting scopes work best)
  • Carmine Alum Lake (dye) – Carolina Biological Supply, pp.758
  • transfer pipette or eyedropper
  • large glass bowls or containers for oysters
  • small cup, beaker, or test tube


  1. Oysters need to be held in a saltwater tank for 24 hours prior to the lab.

  2. Prepare the dye suspension by placing 0.1 g of carmine alum lake and 5 ml of seawater from the oyster tank into a small cup, beaker, or test tube. Mix until all of the dye is suspended.

  3. Carefully shuck the oyster taking care not to damage any tissues. For help, see step 11 of the Oyster Anatomy: Internal Laboratory.

  4. Remove the right valve. The oyster should be lying in the left valve or "on the half shell" (Figure 1). Place the oyster in a glass bowl or other container submerged in seawater from the oyster tank.

  5. Locate the gills and the region of the mouth (for help, see step 14 of the Oyster Anatomy: Internal Laboratory). Make a hypothesis about the fate of the dye once the oyster begins to filter it from the water.

  6. With a pipet or eyedropper, gently add two drops of the dye suspension to the posterior end of the gills. Try not to touch the gill tissue with the pipette or dropper (Figure 2, Figure 3, Figure 4).

  7. Observe the process of filtration and particle movement under a stereomicroscope. You will see the action of the gill cilia and mucus as it transports particles of dye toward the mouth.




Write a conclusion about the fate of the dye and how the oyster altered it. What importance does this process have for the health of the Bay?


Oyster Anatomy Laboratory, interactive lesson on oyster anatomy and how to properly "shuck" an oyster.

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Selected by the SciLinks program, a service of National Science Teachers Association. © 2001.