Definitely not the best looking creatures, the sea lampreys have a unique secondary sex characteristic to help them mate better.
A research team from the Michigan State University has discovered how a male sea lamprey creates heat when it approaches a female sea lamprey, which makes them practically irresistible.
The male sea lampreys possess a small bump (also known as rope tissue), located near the anterior dorsal fin. This tiny bump, which was previously thought to be ornamental, actually works as a secondary sex organ, which generates heat, and makes it hard for the female to say 'no.'
Originally, it was believed that the male sea lampreys managed to attract their female counterparts by releasing pheromones.
The research team closely examined the bump, and discovered that it was full of fat cells, similar to those found in mammals, which play a role in maintaining body temperature.
They further evaluated the temperature rise generated by the bump by inserting a probe into the bump. A 0.3 degree Celsius temperature rise was noted when the male sea lamprey approached the female.
"We thought it was just a structure that was used for some kind of mechanical stimulation that they needed to trigger the female to lay eggs," a professor of fisheries and wildlife, Weiming Li, explained.
Sea lampreys, which are basically parasitic, destructive invasive species, need to have controlled growths. Closely resembling 18-inch eels, these parasites, with their sharp sucking discs and teeth, attach themselves to the host fish, and suck out their body fluid.
The sea lampreys can kill around 40 pounds or fish, sometimes even more, and some scientists also assume just one from seven host fishes survive an attack of a sea lamprey.
Being held responsible for the extinction of certain species of fishes (around three different species), including whitefish, the population of these sea lampreys need to be controlled.
Every year, the US and Canadian government shell out $10-$15 million specifically on lamprey control.
This study, which is expected to be extended further, may help scientists better understand the reproductive biology of the sea lamprey, and find a way to reduce their rapidly growing numbers.
The findings of the study are published in Journal of Experimental Biology.