A recent study reveals that parasites living in the eyeballs of fishes are in charge of its behavior, controlling their host from inside their eyes. When the parasite is still young, it does everything it can to help its host survive from its common predators. However, when the parasites start to mature, they try their best to have their host fishes get eaten by birds, so they can continue their lifecycle.
A Vicious Cycle
The eye larvae ‘Diplostomum pseudospathaceum’ has a lifespan that occurs in three kinds of animal species. Initially, these parasites will breed in the digestive tract of birds and will shed their eggs in its feces. These eggs will then hatch in the water and the larvae inside will start to search for freshwater snails that they can infect. They will then grow and reproduce inside the snails before they find a way to escape into the water again to hunt down fishes, which are their next host.
These parasites enter fishes through their skin and then they travel to the lens of their eyes to protect themselves until they mature. These fishes will then be forced to feed themselves to birds – and the cycle begins all over again.
The Revealing Studies
Mikhail Gopko of the Severtsov Institute of Ecology and Evolution in Moscow, along with his colleagues decided to compare immature larvae-infected fishes to the uninfected ones. They found out that the infected fishes were less active, which made it difficult for the predators to catch them.
On the other hand, the researchers conducted another study involving mature larvae-infected fishes this time around. They discovered that these fishes swam more actively than their counterpart and remained closer to the surface of the water.
To determine if their theories are real, they imitated a bird attack through a swooping motion with a shadow over the tank – and the fishes froze, both infected with mature and immature larvae. Although, fishes with immature anomalies who are not yet ready started swimming again shortly after.