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An apparatus for testing the effects of drugs on the ciliary beating rate of clam gills has been modified to rapidly (15 min to 1 h) assess the effects of water quality factors on a sensitive organism, the fingernail clam, Musculium transversum. The gill and adductor muscles of the clam are excised and placed in a petri dish through which a continuous flow of molluscan Ringers solution or a test solution can be maintained. Normal ciliary activity of the gill preparation can be maintained for at least eight days. The ciliary beating rate is determined by synchronizing the rate of flashing of the substage lamp of a microscope, with the rate of beating of the cilia. Synchronization is achieved when the metachronal ciliary wave appears to stand still.
The first water quality factor selected for testing by the rapid method was potassium, because potassium concentrations are higher in the Illinois River where fingernail clams have largely died out, than in the Mississippi River where the clams are still abundant. The apparatus provided statistically reliable results in a short period of time. There are significant differences in the responses of large (7 to 11 mm) and small (1 to 5 mm) clams to: (a) removal and subsequent addition of potassium, (b) variation of maintenance dosage of potassium in the washing solution, and (c) lag period of response to a specific dose. The results suggest that an intracellular trans-membrane potential change (surface effect) is necessary to activate ciliated cells of small clams. This latter change in small clams would account for the relatively short lag period for potassium activation. Potassium levels required for maintenance of a basal ciliary beating rate are 10−3 M (39.1 mg/litre) for small clams and 10−6 M (0.039 mg/litre) for large clams. Greater concentrations are cilioinhibitory. Lesser concentrations are generally cilioexcitatory, but concentrations less than 10−3 M (0.00039 mg/litre) and 10−9 M (0.000039 mg/litre) are insufficient to sustain basal rates in large and small clams, respectively.
Potassium concentrations in certain rivers, such as the Illinois and Mississippi, are high enough to cause cilioinhibition in gill preparations from large fingernail clams. Inhibition of ciliary activity in intact clams would impair feeding and respiration.
The effects of potassium on the survival, growth, and reproduction of intact fingernail clams are currently being determined and will be related to the effects observed by means of the rapid method.
aquatic biology, water pollution, water analysis, water quality, water pollution effects, bioassay, bioindicators, animal physiology, fingernail clams, Musculium transversum, (Sphaeriidae), cilia, gill, potassium
Assistant professor of anatomy, Southern Illinois University, Carbondale, Ill.
Assistant aquatic biologist, Illinois Natural History Survey, River Research Laboratory, Havana, Ill.