Use love traps to kill 'water vampires'

Thanks to a synthetic chemical, US scientists can destroy aggressive fish that live on the blood of other species, causing the decline in freshwater fish in the largest lake in the United States.

A sea rock grouper in the Great Lakes region.Photo: arkive.org.

Sea-rock grouper (also known as water vampire fish) is a parasite on animals that live in the Great Lakes (including 5 freshwater lakes in the border between the US and Canada). The natural lifespan of sea rock grouper takes place in both freshwater and saltwater environments. They were born in streams and grew up in the ocean.

Previously, sea lamprey only appeared in the Atlantic Ocean, but they accidentally entered the Great Lakes after it erected the Erie Canal to connect the region with New York in the early 19th century. Rocky grouper survives in freshwater environment. In the ocean sea bream is a predator of many fish. But in the Great Lakes they were not hunted by any species.

Sea grouper teeth grow thickly around the mouth. When hungry, they use their mouths to cling to other fish's skin and put the sharp tongue through the scales to suck blood. Usually the prey often dies after the blood of the grouper's blood.

The 'invasion' process of the Great Lakes seabass was completed when several other channels were dug to connect the lakes together in the early 20th century. Soon after, the number of native fish species decreased. fast. During the life of parasites, each stone fish can eat up to 20 kg of meat from other fish. If given the money, the amount of native fish killed by rocky grouper each year can reach several billion USD. According to calculations by scientists, efforts to control the raging of rocky grouper amounted to 20 million USD per year.

The corpses of two fish were sucked by blood grouper.Photo: biology.duke.edu.

By the time of estrus, the grouper finds a stream to breed and die. Salmon always return to the stream where they were born to give birth, but rocky grouper is much more 'easy', because they are ready to lay eggs in every stream if it is suitable. Many scientists believe that sex pheromones help sea breams select streams suitable for reproduction.

Many measures have been taken to destroy rocky grouper, such as spraying chemicals into streams, laying downstream streams to prevent their migration, releasing unproductive males to reduce muscle mass. mating of children. However, these measures do not bring satisfactory results.

Some experts from the University of Michigan (USA) came up with the idea of ​​using sex pheromones to kill sea bass. "Scientists have done a lot of research on pheromones in animals, even humans. But they all assume that animal behavior is quite complex and influenced by many factors, not just pheromones. " Professor Weiming Li, the lead researcher said.

The grouper's mouth kicks.Photo: umich.edu.

Weiming and his colleagues synthesized a hormone produced by male sea breams during estrus. They set up traps in a place where grouper kicked and spawned and put hormones into the trap.

'We think of trapping icefish with pheromone because many scientists have applied it to insects. Females are willing to rush to streams that are conducive to breeding if they smell sexual pheromone. We take advantage of that behavior to set traps , 'Weiming said.

The results showed that the grouper kicked off to swim to the stream when it smelled of hormones. Some of them come into the trap. Weiming's group will conduct a larger trial, in which they use pheromones to trap the female grouper in 20 streams into the lakes. This trial is expected to take place in 3 years.