I’ll be honest, I originally picked this animal solely because of its name. I mean, what kind of name is plainfin midshipman? Its ridiculous. It doesn’t even tell you at all what kind of animal it is. Well, I guess it lets you know the animal has fins, but that’s about it. When you dissect the name, however, it becomes far less random, and thus, less exciting. But, the actual animal is pretty cool, so that’s okay.
It turns out that the plainfin midshipman is a type of fish. It’s called a midshipman due to the presence of photophores on their body. Photophores are light producing organs, most often used by deep sea creatures to attract prey (think of the anglerfish). That’s how it got its name, actually, since the photophores apparently look like buttons on a naval uniform, hence midshipman. The plainfin part pretty much speaks for itself, I’m assuming that it’s because the midshipman has, well, plain fins.
The plainfin midshipman is an ugly fish, and spends the day burrowed under the sand in intertidal zones (probably to hide its bad looks from the light of day). At night it comes out to feed, using those photophores to attract prey. Here’s a picture of the fish to show you just how pretty it is:
Plainfin midshipman come in three types: females, type I males and type II males. Type I males are much larger than type II males, while type II males have vastly larger reproductive organs. The two different types of males use different reproductive strategies. Type I males are territorial and use specialized vocalizations to attract females. Type II males are much cleverer, disguising themselves as females and sneaking into nests to fertilize previously laid eggs.
The most well-known and well-studied feature of the plainfin midshipman is its vocalizations. Those calls that type I males use to attract females are complex and central to reproduction in the fish. The midshipman can produce a variety of sounds, including low grunts, and hums that can last upwards of an hour. These calls can be so loud that they have been known to wake houseboat owners. Not too shabby for a 10 inch fish that spends its time floating just above the seabed.
It seems the plainfin midshipman cannot mate without the use of these vocalizations. Rising hormone levels in type I males lead to the onset of vocalizations, which are designed to attract females. Once the males produce the sound, hormone levels in the females change, and cause the lady fish to develop a special sensitivity to the male’s calls. She then lays her eggs in the male’s nest, and he fertilizes them.
The sound system of midshipman fishes turns out to be similar enough to humans, and simple enough, that they are used as model organisms to study human speech and hearing. Through research on the midshipman it may be possible to better treat people who have lost speech or hearing because of damage to the brain.
Whatever the case, I think plainfin midshipman deserved a post, and not only because of the name. One day I’d like to be out on the ocean listening to the soothing calls of midshipman. I’m putting that on my list of things to do before I die.