Election Section

Deciphering the Call Of the Toadfish By JOE EATON Special to the Planet

Tuesday August 09, 2005

Sausalito may have forgotten about the humming toadfish—the Toadfish Festival with its marching kazoo bands is history—but Andrew Bass hasn’t. The Cornell biologist, formerly at the Bodega Marine Laboratory, is still learning unexpected things about this curious creature and its perceptual world. 

The toadfish is more properly known as the plainfin midshipman (Porichthys notatus). There is also a specklefin midshipman. It’s a homely bottom-dweller with a flattened head, a gaping mouth, and bulging eyes; “very distinctive and fairly unattractive,” says marine biologist Milton Love of UC Santa Barbara. Love, something of a standup ichthyologist, is the author of the indispensable Probably More Than You Want to Know About the Fishes of the Pacific Coast, in which he describes some of the midshipman’s quirks. 

Their sides and bellies are covered with dots called photophores that produce a blue-green light—but only if they’ve eaten the right kind of ostracod, a planktonic crustacean. The ostracod manufactures the bioluminescent chemicals; the fish only stores them. The lines of photophores supposedly resemble the buttons on a naval uniform, hence “midshipman.” There’s also that venomous spine on the gill cover, which doesn’t prevent the midshipman from being eaten by everything from loons and murres to sea lions and elephant seals. Love says friends of his who have sampled the fish were not impressed. 

But it’s the hum that made the midshipman notorious. In late spring and early summer, males travel from deep water to the shallows and begin their courtship. They use their swim bladders to produce a sound which has been variously likened to revving motorcycles, chanting monks (I suspect Tibetan Buddhist, although this was not specified), and a whole orchestra of oboes. If you happen to live on a houseboat moored above the spawning grounds, this can be distracting. In a 1994 article, Bass and Richard Brantley of Cornell characterized the hum as having a fundamental frequency of 100 Herz, sustained for up to 14 minutes. 

This is music to a female midshipman’s ears. Females are attracted by the hum to nests the males have excavated under near-shore rocks. They lay a clutch of 200 or so eggs on an overhanging ledge as the male fertilizes them, then depart. On average, five to six females may use a single male’s nest, but up to 20 have been recorded. The male dutifully guards the eggs until they hatch in a couple of weeks, then keeps an eye on the fry for another month until they’re independent. He stays at his post even at low tide, having a limited air-breathing capability. 

That’s what a Type I male does, anyway. Bass and Brantley also described a second type of male with a very different mating strategy. 

Type II males don’t hum, build nests, or defend eggs. They’re smaller than Type I’s, and their only vocalization is a grunt similar to that of the females. A Type II male hangs around the nest of a Type I until a female enters, then either sneaks in for a quick fertilization or broadcasts his sperm from the nest entrance. (The Type I male is either preoccupied with the female or mistakes the Type II for another female).  

Any eggs the Type II manages to fertilize are cared for by the Type I as if they were his own progeny, which makes the Type II a cuckoo-like reproductive parasite on his own species. Type II’s invest more than Type I’s in sperm production: a Type II’s testes make up 8.3 percent of its body weight, as opposed to 1.2 percent in Type I’s.  

With variations, such goings-on are widespread among fish. Spawning by “sneaker” males has been observed among coho salmon, desert pupfish, sunfish, wrasses, and cichlids, among others. 

Stanford biologist Joan Roughgarden regards these different male types—and multiple female types in some other species—as distinct biological genders. Gender, though, is a conceptual minefield that I’d just as soon stay out of.  

Andrew Bass and Joseph Sisneros of the University of Washington reported in Science last year that a female midshipman’s response to the male’s hum depends on her hormonal levels. Without high levels of estradiol, the natural form of estrogen, they are apparently unable to hear the sound, or at least its higher-frequency components. Bass told a reporter that this finding could have important implications for hearing loss in older women. 

More recently, Bass (with his colleagues M. S. Weeg and B. R. Land) has figured out how the male fish avoid deafening themselves with their own hums. With sustained drones of up to a quarter-hour, you’d think the midshipman would miss out on other acoustical cues that might signal approaching predators. Not so, according to the research team’s recent article in Neuroscience. Nerve impulses from the brain to the swim bladder, generated 100 times a second, produce the hum. At the same time, the same part of the brain signals the hair cells of the ear, inhibiting their sensitivity to sound. The synchronization is perfect.  

Neurologists had known that humans have a reflexive protection against sudden loud noise, tightening muscles in the inner ear that reduce the sound-transmitting efficiency of the eardrum and inner-ear bones. But this response weakens with repeated exposure, and doesn’t work for the sounds we produce ourselves that travel through the bones of the head. The mechanism discovered in the midshipman blocks the sound of the fish’s own “voice”, though. We may have something similar going on; if so, says Bass, it might play a critical role in how we learn to speak, and how we recognize our own voices. 

So this ugly, noisy fish may have useful things to tell us about the sense of hearing in humans. That seems like a fair trade for a few sleepless summer nights on the Sausalito waterfront.