With horn-like facial fins and a diamond-shaped body that stretches about 30 feet in diameter, manta rays are one of the strangest fish in the ocean. But the most puzzling feature of this giant creature is its whip-like tail, which is as long as the rest of the fish's body.
It has long been a mystery why manta rays and related rays have such long tails. Fish do not use their tails to propel themselves through the water or attack potential predators. And while the stingray's tail has a fearsome reputation for having a deadly sting, the manta ray's tail has no defensive barbs at all.
Instead, these elongated tails may act as finely tuned antennae, specialized for detecting approaching danger. In a paper published Wednesday in Proceedings of the Royal Society B: Biological Sciences, two researchers analyzed the tails of cowrays, a smaller relative of manta rays. Researchers found that this elongated structure contains specialized organs that help sense underwater stimuli, suggesting how other marine rays use their hindlimbs. .
“The complexity inside the tail was quite surprising,” said study author Julia Schomell, a marine biologist at Harvard University. “I didn't know that this huge structure had sensory capabilities.”
Most species of stingrays live near the ocean floor, but manta rays and other members of the ray family spend most of their time in the open ocean. These fish flap their enlarged triangular pectoral fins to fly through the water and travel long distances.
Most stingrays have short, muscular tails that they use to bend their venomous spines, said Matt Ajemian, a researcher at Florida Atlantic University who studies sharks and rays. However, the Myriobat line has a very different flip side.
“When you pick it up, it's almost like a giant noodle, but it becomes very hard in the water,” said Dr. Ajemian, who was not involved in the new study. “No one really knew what this tail was used for.”
To understand this anatomical feature, Dr. Schaumel and colleague George Roeder took a close look at the tail of the cownose ray, a type of stingray with a sturdy bilobed snout. They dissected the tails of several pickle specimens in the collection of the Harvard University Museum of Comparative Zoology. They also acquired two recently deceased rays. They created three-dimensional micro-CT scans of the tail and cut thin slices to study its tissue structure.
The research team discovered a hole in the hard tissue of the cow ray's tail. 3D scans revealed that these holes are connected to the fish's lateral line canal, a sensory organ found in fish and amphibians. The lateral line runs the entire length of the fish's body and is connected to receptors in the fish's skin to detect the movement of water around it.
In most aquatic vertebrates, the lateral line is most complex near the fish's head and becomes more streamlined as it approaches the tail. But in the cowray, a more complex system ran the length of the tail and branched into pores in the fish's skin.
The researchers claim that this network helps the ray's tail to pinpoint stimuli in the water around it. This is especially useful when cownose rays descend to the ocean floor to scavenge burrowing bivalves. Burying their heads in the sand exposes the rays to predators.
A finely tuned antenna protruding from the backside helps the beam detect trouble before it's too late. “When a shark attacks from behind, there's this big water movement that tells the rays it's time to move away,” says Dr Schomell.
Dr. Ajemian agrees that it is plausible that cownose ray tails function as antennae, but this is a bit surprising since his team often encounters rays with damaged or missing tails in the wild. be. “I thought the tail would come off easily,” he says.
Dr. Schaumel believes there is more to the tail than early warning. Her team is analyzing other species, including manta rays, to see if these structures, like kite tails, help these fish stabilize as they swim.
