Skate

A small skate shows off its camouflage. Image taken at the Monterey Bay Aquarium.

This flat sandy colored fish is one of many types of skates. Sometimes these fish bury themselves in the sand, with just their eyes and spiracles sticking out. Spiracles are the holes behind their eyes that pull in water to push across their gills so they can breath while sitting still. Several species of skates have been found to have electrical tissue in their tail. So they can produce electrical energy (much more than is required for simple muscle movement), but no one has ever been shocked by a skate and at the moment, we don’t really know what they have this ability for, although it is thought that it might be for reproductive and social interactions.

 

skate

This skate swims over us in a large tunnel at the Aquarium of the Bay.

Skates are closely related to rays and sharks. Just like rays and sharks, their skeleton is made of cartilage, which is more flexible and lighter weight, instead of bones. They have several gill slits visible instead of a gill cover. You can tell the males from the females the same way (by looking for claspers-long, thin protrusions on their underside). And the coolest similarity, is that they can detect electricity. If you look closely at the last picture, you can see small golden spots on the underside of the skate’s body. In this picture, you can see them most clearly around its mouth. These spots are the ampullae of Lorenzini. These spots can pick up very small electrical pulses, so if the skate is hunting and there’s an animal buried in the sand but the skate can’t see it, or smell it, or hear it, it can still detect the electrical pulses from its heart beat. But then what? Well, notice the two holes above its mouth that look like the eyes of a happy face? Well, their eyes are actually on top of their head and these holes are its nostrils. They can actually shoot jets of water out of their nostrils to push sand away and find food living underneath, such as clams. Another trick they have is to cup their wings toward the sand creating a suction cup to pull the sand away. This little trick has led to many disappointed fishers, because the great force required to dislodge this fish when it’s suctioned to the ground makes them think they are getting a much bigger fish than they actually are.

Although skates have a flattened body shape similar to a ray and are closely related to rays, they have their own separate order. A couple of major differences help to distinguish them. One is that skates will never possess a venomous barb, while many rays do (manta rays have lost their barb). The other is that skates lay eggs, while rays give live birth.

Skate eggs are particularly cool. They are often called mermaids purses. One cool trick aquariums like to do is replace part of this leathery egg with clear plastic so that we can watch the embryo develop. Here is a video of a skate embryo, inside its flat sea weed-looking egg:

Is that cute or what? That little yellow ball in the middle of its chest is the yolk, which is giving the embryo nutrition. When that ball is gone, the embryo will make its escape through the sides of the egg and emerge as a miniature version of the adults. Some skate eggs can have as many as 7 embryos in them! That’s pretty cramped.

While watching these embryos develop, scientists noticed that they go through a number of stages very similar to shark embryo development before continuing on to a skate shape. Also, they discovered many malformed skates, where their embryonic development was arrested and they looked like a cross between a shark and a skate. Based on this, they believed that rays and skates evolved from a shark ancestor. However, the molecular studies now show that they share a common ancestor with sharks rather than evolved directly from an ancient shark species, so they are not modified sharks.

If you are interested in learning more about skates, the Florida Museum of Natural History has two great pages filled with ray and skate information here and here.

Lastly, skates are not a sustainable seafood, as they are overfished and frequently caught with high amounts of by-catch. Read more about this here. Are you eating imitation scallop? Imitation scallop is just one of the common market names for skates. The rest can be found at the aforementioned site. How is this vertebrate being misidentified as a shellfish? Well, if you can’t sell skate to consumers, use a cookie cutter to cut out chunks of a skate’s wings and call it scallop. Apparently, it works.

About these ads