A Little Bit More
It’s not at all difficult to identify this unusual fish – it’s hard to imagine anyone mistaking it for anything else! Paddlefish have had a variety of names in the past and, as you might expect, most are focused on its paddle. In various places across North America, people have called it a spoonbill, spoonbill cat, and shovelnose, among others, but Paddlefish seems to be the common name that has the greatest following today.
Despite the fact that this large fish - they get up to 100 pounds or more - is so distinctive, the function of its paddle eluded scientists for years. In recent years, researchers were able to place fish in special tanks to see how they oriented to food. It was soon evident that the fish weren’t simply straining water in the “hope” of obtaining food, they were able to home-in on specific food items quite accurately using their electrosensory cells on their paddle and head. Although scientists have known that several species of sharks key in on electric signals from prey hiding beneath the sand, no one knew that Paddlefish were using a similar sensory technique. But don’t get the idea that Paddlefish are using this sensory ability to track down individual planktonic animals. Plankton is usually found in large concentrations and these are often large enough to make a real meal for Paddlefish, once they’re found.
As settlers moved into the heart of the North American continent, they found the Mississippi, Missouri, and Ohio Rivers and their tributaries had especially large numbers of Paddlefish living in some of the quieter, backwater areas. Since Paddlefish won’t take a hook like typical fish, people soon learned to net these fish and discovered that their roe (fish eggs) was delicious, much like sturgeon caviar. Today’s many changes to the streams across North America, especially the dams that prevent spawning runs, has dramatically reduced Paddlefish numbers but current conservation projects are underway to bring Paddlefish back into many of their former waters.
Activities
Plankton Scoop
Objectives: See how a filter-feeder picks up tiny bits of food
Materials: Materials: Dish pan or sink, tap water, pencil sharpener shavings, an old toothbrush
As the result of many TV programs on baleen whales, the feeding activities of whales are well known by school children all over the world. Almost everyone knows that the largest of all the whales, the Blue Whale among others, feeds on small creatures that it filters out of the water. The Paddlefish, accomplishes the same task, collecting and swallowing small creatures that are floating in the water column, but does so in a different way. Instead of the hair-like projections within their mouths, called baleen in whales, Paddlefish have small projections on their gills, called gill rakers that act as a kind of screen to remove plankton from the water. As these fish swim through the water with mouth wide open, water and plankton move into their mouth , into their throat and then pass out through their gills. The gill rakers screen this water, catching any floating plankton as the water moves through.
Visualizing this process may be a bit difficult for some so why not see if we can simulate what is happening, at least to some small degree. This is a very easy exercise that students can engage in that I hope will demonstrate how effective filter-feeding actually is.
- Fill a dish pan or sink with tap water
- Take the shavings from a pencil sharpener and sprinkle a heaping tablespoon’s worth into the water
- Gently move the shaving around so they are spread throughout the water (most will float on or near the surface)
- Ask your students what would be an efficient way to gather up all of those shavings. Allow the students some time to see what they might come up with to accomplish this task. Remember, they need to do so efficiently, they can’t pick up one piece at a time or “they’d starve to death”!
- Now, take an old toothbrush and have a student move the brush sideways gently through the water to concentrate and pick up the shavings (our artificial plankton). It should be readily apparent that this is a very effective and efficient way to gather up “plankton”
The idea here is to see how effective the brush, which acts much like the Paddlefish’s gill rakers, is in scooping up the individual bits of food. If a large animal is feeding on really small food items, it needs to be especially efficient in obtaining that food or there will be too much wasted energy for what is gained.
Key Concepts
Adaptations and Diversity, Identification, Predator/Prey Relationships, Structures and Functions
Questions
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Posted by Somes Michael on March 23, 2006 at 02:04 PM
Q: Do frogs and toads pass out when they are on their backs?
A: Well, they don't actually "pass out" but they do stop moving and seem to be in a trance-like state. I've never done this myself but I've heard of people who have gotten frogs, toads and lizards to do this. Of course, there's a biological reason that makes sense. Reptiles and amphibians don't have diaphrams, a muscle that allows us to draw air into and force air out of our lungs, so they use their torso muscles to fill and empty their lungs. When a toad or frog is on its back, this position makes breathing difficult so to reduce its oxygen needs, the animal simply goes into a trancelike state. Hope that helps. Thanks for asking.
Posted by Olivia, Fletcher on March 30, 2005 at 01:23 PM
Q: How do frogs make their cheeks so big?
A: Basically, it's the same as you can do. Hold your mouth shut, then force air from your lungs into your mouth without letting it escape. When you do, you'll find your cheeks puffing out. Well, a frog does something quite similar although it does it to make their croaking sounds in spring and also to intimidate (I'm a bigger, meaning frog than you are) other male frogs. Hope this helps.