In Belgium there are four known species of newts, the most threatened of these being the Great Crested Newt, whose populations have greatly declined in Wallonia over the last few decades. The Alpine newt is more tolerant but its populations are also in decline. Discovered in the 18th century in the Austrian Alps – from where it gets its name - it is in fact present up to the coast in Belgium and elsewhere.

“Like most animal species, newts occupy a place in the food chain”, explains Mathieu Denoël. “They act as an intermediary between aquatic and land-based ecosystems, by transferring energy and feeding on small invertebrates such as mosquitoes and bloodworms… In this way, they participate in the control of natural populations of other species. They are at the core of a balance that has been established over a long period. However, this balance has been altered. For the moment, we do not know what the final consequences of the disappearance of a species from an ecosystem will be”.

This brings us to the second actor in the play: the goldfish (Carassius auratus).  This fish, which is used for ornamental purposes and can grow bigger than 20 cm in the natural environment, (it is affected by dwarfism in aquariums), cannot eat adult Alpine newts (1) because its mouth is not of sufficient size. On the other hand, it eats their eggs and larvae. Carassius auratus is the most commonly introduced ornamental species into pools and ponds. Very resistant to cold winters, it easily adapts to these environments.

Preferably in the bedroom

The play can now be acted out: numerous studies carried out in different natural environments, with or without goldfish, showed that the presence of such fish, even though they are small, causes a decline in amphibian populations. However, the underlying mechanisms behind this were as yet unknown. This mystery roused the curiosity of researchers from the Laboratory of Fish and Amphibian Ethology. “One way for amphibians to survive in an altered environment is to develop anti-predator strategies, notably in terms of behavior. Indeed, it has been shown that avoidance behavior reduces the possibility of being detected by a potential predator but very little is yet known about the consequences of this for sexual behavior. In the study we carried out, we tested the hypothesis that the Alpine newt uses shelters more often and exhibits fewer courtship displays in the presence of goldfish”, indicates Laurane Winandy.

To conduct this laboratory experiment, the results of which were published very recently in the journal PLoS ONE (2), the researchers from Liege used 24 aquariums. Twelve of these contained 4 newts – 2 males and 2 females - and a goldfish of around fifteen centimeters in length. The 12 other aquariums contained 2 male newts and 2 female newts only. In addition, each aquarium was fitted with a shelter behind an oblique stone enclosed by a grid preventing fish access.

The objective was therefore to determine whether the presence of a goldfish in the aquarium was likely to affect the reproduction of the newts and, by extrapolation, to cause a decline in their populations in the natural environment. More precisely, the interest of Laurane Winandy and Mathieu Denoël focused on the interaction between the two species. Firstly, how was the newt going to use the habitat (in particular the shelter) according to the presence or non-presence of the fish? Secondly, to what extent did cohabitation with the goldfish influence the frequency and occurrence of courtship displays by the newts?

 (1) The average size of Adult alpine newts is 8 to 12 cm.
(2) Winandy, L, & Denoël, M. (2013). Introduced goldfish affect amphibians through inhibition of sexual behaviour in risky habitats: an experimental approach. PLoS ONE, 8(11), 82736.