Looking Through a Windowpane Flounder

Looking though a juvenile windowpane flounder with a flashlight. The stomach and spine can clearly be seen. 

By Joe Reynolds
www.nyharbornature.com

​Although the friendly flounder from the classic Disney movie, The Little Mermaid, will probably not be found swimming around New York Harbor, there are several fascinating flounders or flatfish that do throughout the year. These fish are normally anything but sociable.
 
Carnivorous bottom-dwelling thin creatures often found solitary on the bottom of the bay or estuary waiting for potential prey to ambush. They have voracious appetites and will strike at a shrimp or other prey when they get too near a flounder’s face.
 
Winter flounder have small mouths, and summer flounder or fluke have large mouths with sharp teeth. Both are sizeable flounders highly prized by anglers. There are also little brown flounders known as hogchokers, not exactly a friendly title. Legend has it this flat fish got its quirky name from farmers who used to feed it to hogs or pigs, but often had difficulty swallowing the fish’s bony body and would choke on the fish’s rough scales. I don’t know who to feel worse for, the pigs or the fish.
 
Another flounder with an interesting name living around New York Harbor are Windowpane flounders or sand flounders. Its curious name comes from young windowpanes being so thin-bodied they appear transparent, enabling a curious person to easily recognize the fish’s internal organs, such as the outline of the stomach.
 
I’m not kidding. The fish is so slim and skinny that if you hold up a juvenile fish to a light source you will be able to see clear through it. Like looking through an opaque glass window. 

​Although these unique flatfish have less muscle than most other flatfish, windowpanes are not malnourished or feeble and should never be confused as a juvenile fluke. Windowpanes have evolved and adapted to living on the bottom of sandy bays by blending in extremely well to their surroundings. Being the color of silt and sand they blend in perfectly well with their undersea environment. 

​Windowpanes have translucent pale olive-green to light brown rounded bodies, with countless small dark spots, some white spots, and many larger spots that go along the length of the body and continue onto the fins. Its underside is uniformly whitish. A coloration that makes the fish well-camouflaged to forage on a sandy or muddy shallow bottom.
 
But playing with pigments is not their only tool to survive. They have a lateral line, used to sense the surrounding environment, which is highly arched, and a wide mouth. When an unlucky sand shrimp, small crab, or small fish swims nearby, a windowpane will quickly open its mouth wide to rapidly overwhelm and gobble down its prey.
 
Flounders are generally shrewd, ravenous predators, and windowpanes are not unlike their larger and more famous cousin, the fluke. Just like the summer flounder both eyes of the windowpane flounder are on the left side of the body, and the mouth points to the left.
 
Similar to both the fluke and winter flounder, windowpane flounder undergo seasonal migrations. During the winter, adult windowpanes will generally move offshore at depths of 140 to 260 feet, but swim inshore starting in the spring following warming water temperatures.
 
Windowpanes have a split spawning season around New York Harbor, with peaks in spring and autumn. They generally spawn at night on or near the bottom of an estuary at temperatures from 60.8 to 66.2°F in the Mid-Atlantic Bight. 

​The fish do not live long. Windowpanes attain a maximum age of about eight years, with females reaching maturity between three and four years of age and males around two years of age. It’s a medium-sized fish, only growing up to 12 to 18 inches long, and rarely exceeding one pound. So people fishing do not readily seek windowpanes as opposed to the meatier summer or winter flounders.
 
Historically, windowpane flounders were harvested for their use as bait, or they were ground into fishmeal. But today their biggest problem comes not from recreational fishing, but commercial fishing. Bottom trawls catch many windowpane flounder as bycatch. They are also prey by larger fish including various sharks, skates, stingrays, cobia, and bluefish.
 
Yet, despite these troubles the windowpane flounder is still abundant and has the distinction of being the slimmest flounder fish to be found in New York Harbor. An unlikely place for such a scrawny fish, but don’t let it fool you. Windowpanes are tough aquatic creatures, swimming and making its home in the busy and bustling waters near New York City.