Invasive and Harmful Species

A species is considered invasive when, having established itself and reproducing naturally in a defined demographic area where it is not native, it becomes a disruptive agent and harms biodiversity.

Thus, certain animal species can seriously threaten the balance of aquatic environments such as rivers, ponds, lakes, reservoirs, and bodies of water in general. This is the case for the American crayfish, bullfrogs, marsh frogs, and catfish.

American crayfish

Nicknamed “the red plague,” it is resistant to various pollutants and environmental changes. Primarily, it serves as a vector for pathogens to which our native crayfish are highly susceptible. It adapts perfectly to all bodies of water, where it digs numerous burrows in dikes and banks. It is a predator of almost all invertebrates, aquatic plants, and certain fish. The American crayfish spawns only once a year but produces between 50 and 600 oocytes.

The catfish

It is commonly considered a voracious, omnivorous, and highly opportunistic species. In fact, it exploits most of the food resources in its environment. It is therefore a predator to all other species. As a result, it causes a systematic biological imbalance in the environment it has taken over. It reproduces once a year, with each spawning producing between 5,000 and 7,000 oocytes.

Bullfrogs and Marsh Frogs

They are the largest frogs in Europe. They measure between 10 and 17 centimeters when fully grown. Highly voracious, their diet includes almost all arthropods, mollusks, amphibians, fish, birds, reptiles, and mammals. They are believed to spawn between once and twice a year, producing between 1,000 and 20,000 oocytes per spawning. Even more concerning, the marsh frog has the ability to mate with native green frogs. If offspring are produced, the marsh frog’s genes are passed on and become dominant. This inevitably leads to the complete disappearance of the native frog.