The American paddlefish is an interesting but relatively unknown fish species. These fish have large paddle-shaped appendages on their foreheads, and they inhabit the murky waters of the Mississippi River and its tributaries. They can grow to six feet (183 cm) and weigh 150 pounds (68 kg). So what is the purpose of the paddle? The electroreceptors of paddlefish answer that question.
You might think that the paddle is a device to dislodge food from river bottoms. Some people called them “shovelnose fish,” assuming they used their paddles as a shovel. But paddlefish don’t dig for food, and lab experiments in 1993 showed the paddle’s real purpose.
Paddlefish are filter feeders that feed on tiny crustaceans and insect larvae that drift through the water as plankton. Many whale species are filter feeders that use comb-like baleen in their mouths to strain their food from the water. Paddlefish have comb-like rakers in their gills. They swim with their mouths open and filter their food from the water. But that doesn’t explain the paddle.
Paddlefish have poor eyesight and no sense of smell, so how do they know where to swim to find food? The paddle is covered with tens of thousands of electroreceptors that can sense extremely minute electric fields. Plankton emit signals that are similar to what doctors measure in electrocardiograms. Paddlefish use their electroreceptors to detect those signals and locate the plankton, even in murky waters.
The electroreceptors of paddlefish are similar to those of the platypus found in Australia. Many marine fish, including sharks, skates, rays, and some freshwater fish, can use weak electrical signals for feeding and communication. Those fish don’t need light or clear water to eat and maintain a balance in the environment. This ability is not something that evolved in the paddlefish because fossil evidence seems to indicate that they had electrosense ability very early in Earth’s history. We are amazed by God’s designs that we see in living things.
— John N. Clayton © 2020
Those of us who have spent many happy hours snorkeling in coral reefs tend to look at the big fish that we see in the reef. Groupers, sharks, rays, and parrotfish attract our attention. We can easily miss what makes the reef ecosystem work so that the larger fish can live there. Scientists are learning about cryptobenthic fish in the coral reefs.