Luminescent Photophores No Longer Necessary : Odd Fish, Melodious Midshipman, May Be De-Lighted by Evolutionary Change

Whistling and grunting as it cruises the blue waters off the California coast, the melodious midshipman, a homely looking fish with a lumpy body and a larger-than-usual head, knows how to get attention.

This fish not only sings, but its nocturnal serenade often is punctuated by a show of lights that the midshipman produces with a bit of flair and a lot of flash.

The operative word here is flash.

As it turns out, those lumps on the midshipman’s body are not evidence of underwater cellulite, but button-like, seafaring headlights “that they are able to flash on at night,” said marine biologist Steve Kamolnick of Sea World in San Diego.

“The midshipman,” he contends, “is not your average fish.”

Indeed, as studies show, the midshipman may be a living example of Darwinian theory in action; marine scientists believe they are witnessing the beginnings of an evolutionary change in the fish that may one day result in the loss of its luminescence.

“He has more than 700 little organs, photophores,” said USC marine biologist Basil Nafpaktitis. “My question is why would nature maintain them?”

Apparently nature asked the same question long ago regarding some of the midshipman’s relatives that inhabit Friday Harbor in Washington and the shallow waters off the coast of Chile because their lights have been permanently turned off.

Because these fish are no longer capable of switching on their lights, scientists believe their condition serves as a clear warning of what lies ahead for the midshipman.

Although Nafpaktitis says he is unable to pinpoint exactly when nature will phase out the lights, he is convinced that it won’t be any time soon.

“Evolution doesn’t work overnight, but we think that this fish probably will lose his capability of bioluminescence. It’s possible that we are looking at the elimination of the photophores by natural selection because they are not important for mating any longer in similar fish.”

Natural selection, the process by which the members of a species that have more favorable variations are better able to survive to produce successive generations, is a key concept in Darwin’s theory of evolution.

“What’s the use of having these exquisitely made photophores if they can’t use them?” Nafpaktitis asks. “Sooner or later nature will step in and eliminate them.”

USC scientists have found that the midshipman obtains the luminescent chemical it needs by eating crustaceans containing luciferin, the same chemical that fireflies produce to manufacture their tiny flickers of green-yellow and red-orange light.

Although the fish is incapable of producing its own luciferin, it can preserve the substance in the red cells and plasma components of its blood for as long as two years.

Nafpaktitis speculates that the lights may also serve the same purpose of the silver bellies of tuna, which supposedly give the impression of shimmering light to hungry predators looking up from below.

The singing midshipman, which got the name because its photophores look like brass buttons on the jackets of naval midshipmen, also has the dubious distinction of causing trouble above sea level.

Some say the nocturnal concert has been the bane of houseboaters in San Francisco Bay who complain that the noise keeps them up at night but, said Sea World’s Kamolnick, “I think that’s probably more folklore than fact.”