For different reasons linked to human activity, amphibian populations are declining to the point of being threatened. The introduction of fish into pools and ponds is one of causes of the problem. During a recent experiment, researchers at the University of Liege conducted an experiment in specially-equipped aquariums to study how the presence of goldfish can influence the reproductive behavior of newts. The results were published in the scientific journal PLoS ONE.
Times are hard for amphibians! Their global decline is undeniable. The phenomenon can be explained by different combinations of causes brought about by the individual set of characteristics proper to each region concerned. One of the main examples of this is the disappearance of habitats. There are fewer and fewer pools and ponds that can serve as breeding sites. In the agricultural environment, intensive crop cultivation and the drainage of land are among the principal causes of the problem. Deforestation should also be singled out as a cause because it affects the reproduction and behavior of certain species such as salamanders. Growing urbanization also plays a non-negligible role in the disappearance of habitats. Moreover, the disappearance of these habitats is very harmful. Pollution, particularly that caused by the use of fertilizer and pesticides, is extremely harmful to amphibians because the skin of most species of amphibians is permeable and plays a vital role in their respiratory system.
Whilst it may appear to be anecdotal evidence at first glance, another important cause of the depletion or even extinction of certain populations of amphibians is the introduction of fish into the natural environment. As Doctor Mathieu Denoël, a research associate at the F.R.S.- FNRS at the Laboratory of Fish and Amphibian Ethology of the University of Liege (ULg), points out, the introduction of exotic species into the natural environment represents one of the major causes of the global loss of biodiversity.
To what extent is human activity responsible for the introduction of fish into pools or ponds that were previously devoid of fish? Sometimes, the introduction of goldfish or other exotic species is done to add “color” to the natural environment. Sometimes it is done to add a new pet to a pool or pond or even sometimes to compensate for a perceived insufficiency of biodiversity in the natural environment. An added problem is that of anglers dumping fish into ponds or adding species of fish to ponds where previously there weren’t any for the purposes of fishing and which might otherwise have become a habitat for amphibians. “Most of the time, it is a lack of information which causes people to act in this harmful way”, comments Mathieu Denoël. “Nonetheless, this kind of activity represents a new threat to amphibians. In many cases, they are disappearing from their natural environment; in other cases, they manage to survive by using anti-predator strategies”.
The arrival of the actors
Before human activity affected their way of life, many amphibians occupied pools, ponds or lakes that were devoid of fish. Therefore they did not have to develop co-habitation strategies. “Whilst it appears that sometimes fish and amphibians can coexist, it was interesting to try to understand how native species react, in terms of their behavior, to the introduced species”, explains Laurane Winandy, research fellow at the F.R.S - FNRS in the Laboratory of Fish and Amphibian Ethology.
This is where the alpine newt (Ichthyosaura alpestris) and the goldfish (Carassius auratus) come into play. Before we write the play, let us first introduce the actors. Newts are amphibians which live their lives on land for most of the year. They hibernate during winter, but when the warmth of spring arrives they enter their reproductive phase. Reproduction takes place in an aquatic environment. The newt reaches a pond and remains there for the “lovemaking season”. In this way the newt is different from other amphibians such as toads and frogs which often only stay in the water for a short period. “Coexistence between toads and fish is more frequent because their tadpoles secrete a toxin which protects them from predation”, explains Laurane Winandy.
