California Singing Fish

Kingdom Animalia
Phylum Chordata
Class Actinopterygii
Order Batrachoidiformes
Family Batrachoididae
Genus Porichthys

Concrete ship hulls on the waters near Sausalito, California vibrated with a hum coming up from the sea floor.

The hum came between 9pm and 5am — nice hours, for those of us who need sleep to survive. Houseboat residents found themselves tormented by something like a B-17 bomber running wide-open under the waves. So imagine their suspicion when the hum started near a Naval base in the state of Washington.

Conclusions were reached. During the 1980s people voiced a number of theories: Government tests, water treatment plants, extraterrestrials.

Eventually all three were absolved of responsibility by recordings of some rather homely fish contracting their swim-bladders.

The California singing fish is known officially as the plainfin midshipman because of the flourescent dots running in rows along its belly like buttons on a midshipman's uniform. The photopheres act as a deterrent to predators by advertising poison. We call that Batesian Mimicry¹ — midshipmen look more poisonous than they really are. The light spots also attract prey, mostly small crustaceans. These are ugly little brutes. They look like giant tadpoles, with purple backs and yellow bellies, achieving a length of ~38cm.

Winters find these fish on the sea floors from the Gulf of California up to Alaska; in the summers they migrate up to the intertidal zone and males begin the dreadful hum that characterizes the mating ritual. The sound is a product of rapid swim bladder contraction — six thousand contractions per minute, twice the speed of a hummingbird's wings. The fish maintain this vibration for hours. This incredible stamina is provided by the structure of the swim bladder's muscle fibers: they're tubes filled with ATP. Batteries of the natural world.

The midshipman's unusual muscle fibers are a source of interest for medical scientists looking to treat degenerative muscle disorders in humans — specifically, nemaline myopathy.

The mating of California singing fish is of paramount interest.

Males come in two forms, named Type 1² and Type 2. Type 1 males are larger and capable of louder humming than Type 2s. Because the hum is really the only tool the midshipman's got for atttracting females, Type 1s are much more popular breeders. They are the alpha males of the midshipman world.

Type 2s are smaller and hum more quietly. They do not attract females. But they fertilize as many eggs as Type 1s, compensating for their lack of appeal by cunning and sheer balls.

I don't say something like "sheer balls" lightly. Type 2 males have enormous testicles - a full 15% of body weight, compared to a paltry 1% in a type 1. To match, yours truly would have to waddle around with some 27 pounds of testicle.

Midshipmen frequently do not mate directly — females deposit eggs in the homes of appealing males, which are fertilized later. Because a Type 2 looks like a female, he is able to subvert the Type 1's territorial nature, enter his den, and fertilize his eggs.

Balls indeed.

The mating ritual is hard on singing fish. While these creatures can withstand great variations in salinity and can survive 24 hours outside of water, the throes of parenthood are frequently more than the little creatures can handle. Scientists have never found a two-year-old female; males emerge from brooding emaciated and exhausted and frequently do not see another spawn.

Recent study has suggested that the transformation of the generic male into a Type 1 or Type 2 results from both genetic and environmental factors. It was once believed that inheritance was linear — 1s spawned 1s, etc. but closer observation shows that once the number of Type 1 males becomes proportionally large enough, other males take on the sneaking and morphologically different characteristics of Type 2s.