Prozac works on clams and mussels.

As far as Peter Fong knows, he's the first researcher to prescribe Prozac to fingernail clams and zebra mussels.

Whether the animals cheered up, the scientist at Gettysburg (Pa.) College declines to say. The popular antidepressant did jump-start reproductive behavior, prompting the fingernail clams to give birth and the mussels to release sperm or eggs. Two other antidepressants, Luvox and Paxil, triggered the same effects. Fong and his students described their findings at the annual meeting of the Society for Integrative and Comparative Biology in Boston earlier this month.

In humans, all three drugs block the molecular mopping up of serotonin, making more of the compound available for transmitting neural messages. Serotonin is known to help regulate bivalve sexual activity, although the underlying mechanism is not clear. Fong sees the antidepressants' effect as a hint that bivalve serotonin chemistry resembles that of humans.

Fong points out that the finding might lead to a cheaper way to trigger spawning. Currently, clam farmers use serotonin at 100,000 to 1 million times the concentrations at which Prozac and Luvox produced results in Fong's experiments.