NOT THE UNIFORM. Called midshipman fish because some varieties of Porichthys notatus have bioluminescent spots that resemble rows of uniform buttons, they are also known as California singing fish and canary bird fish. Females probably aren't attracted to the uniform but rather to the male's song.

PICENE BOOMBOXES. When the midshipman migrate from the deep Pacific waters to the west coast of North America to mate each summer, the intertidal zone becomes a noisy place. Courting males hum to attract egg-laying females. The love song, described as a motorboat-like drone, comes from rapidly contracting muscles on the male's swim bladder and proves irresistible to female midshipman. Each female deposits all her eggs for that season in one nest and swims away. Hoping to lure more females to the nest, the male resumes singing, all the while remaining on guard until the offspring hatch and mature.

SNEAKER MALES. Not guys in Air Jordans but morphs with an attitude, the so-called Type II or sneaker males are smaller and less vocally talented than Type I males. Unable to attract females because they can't sing, sneaker males hang around nests where Type I males are humming and quickly dart in to fertilize some eggs. They frequently get away with this behavior, probably because they closely resemble the smaller females.

THAT TAKES TESTES. What sneaker males lack in vocal repertoire and size, they more than make up in reproductive capacity. Studies at Cornell have shown that the gonads of Type II sneaker males comprise up to 15 percent of their body weight, compared with only 1 percent in Type I males. The equivalent in a 150-pound human male would be 22.5-pound testes.

BIG VOCABULARY. Don't think humming fish hum because they don't know the words. They produce two others kinds of vocalizations that, if not especially eloquent, do get the message across: A series of grunts that bioacoustic scientists call a "grunt train" and a low growl both come from Type I males guarding their nests. Type II males have been heard making an occasional grunting sound but always in non-spawning situations.

ALL EARS. Only certain fish species are capable of vocalizing, but virtually all fish have ears to keep them in tune with their sound-filled environment. Cornell biologists who conduct acoustic playback experiments with midshipman fish in outdoor aquariums report that female midshipmen are easily attracted to their computer-synthesized hums. But simulated grunts, they say, "seem to do nothing for the females."