June 27, 2013
Vampire Fish Like It Hot
Michael Harper for redOrbit.com - Your Universe Online
Male sea lampreys, often called vampire fish, have a long ridge running across their backs that contains a long row of brown fat cells. Other animals also have stores of brown fat similar to the ridge found on the male lampreys. In mammals, this fat is used to regulate body temperature and warm the animal when their surroundings are too cold. Scientists from Michigan State University (MSU) were curious why the male lampreys had this store of fat, called rope tissue, as they have no need to use this fat to keep themselves warm. After conducting some research, Weiming Li, a professor of fisheries and wildlife and a team member at MSU, discovered that male lampreys heat this row of rope tissue to attract females just before mating. Professor Li's research is now published in the Journal of Experimental Biology.
"We initially thought this might be a mechanical device," said Li in a press statement.
"Females are more passive [and] the male will wrap its body around the female's belly - almost like he's stripping the eggs out of her."
After attaching some probes to this rope tissue, the MSU team discovered the temperature of this tissue increased by as much as 32 degree Fahrenheit when in the presence of a female lamprey.
The researchers even found that the temperature increase is directly proportional to how attracted the male lamprey is to the female.
If this warmth attracts a female, the male lamprey attaches himself to her head with his primitive mouth, which contains many rows of teeth and a rough tongue. The two then begin to writhe around and finally emit sex cells that combine and develop in the nest.
Lampreys are andromous creatures, meaning they are born in fresh water and migrate to the sea for their adult lives. They return to freshwater when it's time to spawn and it is here where they eventually die.
Li said he wanted to conduct this research to better understand how lampreys mate so they can find better methods to control the population of these species. Though relatively welcome in other parts of the world, these 18-inch long lampreys are considered a parasitic animal in the Great Lakes region. The sea lampreys get their vampire nickname from the way in which they feed on other fish in their ecosystems. They attach themselves to passing fish with their mouths, biting down on the fish and scouring its scales with their tongue where it then feeds on blood and other body fluids. Though fish can survive this attack, not many do. According to the MSU press release, only one in seven fish survive an encounter with a sea lamprey.
With no natural predators in the Great Lakes, lampreys can kill up to 40 pounds of fish in their life times and are responsible for the extinction of two species of whitefish. The US and Canadian governments estimate they spend about $10 to $15 million a year on lamprey control.
"I have been involved in lamprey biology for many years and I really believe you should know your enemy," said Li in an interview with the BBC.
"Because the reaction is so apparent, I suspect the male is sending a signal so if we can find a way to stop this signal then we can probably have an effective way to stop them from reproducing."