Some marine mammals have been known to leave their natural ecosystem in pursuit of prey. Killer whales and bottlenose dolphins have been observed voluntarily and momentarily beaching themselves when prey leads them onto a beach. However, this type of action has not been commonly observed in freshwater fish species.
There are some freshwater fish that hunt for food outside of the water, such as the archerfish, which shoots down insects into the water with droplets from their specialized mouths, but it never has to leave the water to do so. Snakehead fish do occasionally leave the water to walk on land, but they are built to do so.
Therefore, the observance of a large-bodied predatory fish leaving their ecosystem to catch prey by French scientists was truly a peculiar sight. In southwestern France, at the bank of the River Tarn where pigeons wash and drink, European catfish, the largest freshwater fish on the continent, lunge at pigeons splashing at the water’s edge much like a crocodile strikes his prey.
View the fish in action in the video below.
Julien Cucherousse, with the Laboratory of Evolution and Biological Diversity at Paul Sabatier University in Toulouse, and a team of researchers observed this behavior and filmed 54 of the attacks from a bridge overlooking the river in the summer and fall of 2011. The study, titled “Freshwater Killer Whales”: Beaching Behavior of an Alien Fish to Hunt Land Birds was published on December 5, 2012 on PLOS ONE.
Fifteen of the 54 observed attacks were successful, meaning the fish successfully captured the pigeon on land, returned to the river, and swallowed the bird. For most of the attacks, the fish did not exit the water more than necessary. In approximately 40 percent of all the observations, the catfish had more than half of its body out of the water and in one attack, a complete stranding was observed, but without a successful capture.
The fish who kill birds in this manner are alien species to the area–they originated from east of the Rhine River in Germany, but were introduced in the River Tarn in 1983 and have flourished since.
This behavior has not been reported in the native range of the species, leading scientists to believe that “some individuals in introduced predator populations may adapt their behavior to forage on novel prey in new environments,” according to the study.