The experience was spread over 12 weeks during which so-called “scan and focal sampling” methods were applied. Altogether, each of the aquariums was the subject of 20 instant observation sessions (scans) per week as well as several hundred video films over the entire reproduction period (focals). “The objective was to see where the individuals were to be found in the aquarium and what they were doing, particularly with regard to sexual behavior”, reports Laurane Winandy.

What were the results of these observations? The newts used the shelter more often in the aquariums they shared with a goldfish. In addition, their courtship displays were a lot less numerous. The lack of courtship displays was much more marked in the open area where there was contact with the goldfish.

An untimely interruption

What was the explanation for this fact, given that the size of Carassius auratus did not enable them to attack adult newts? Was it because the newts anticipated the danger posed to their eggs? “The first fact to be highlighted was the stress experienced by the amphibians when faced with an unknown animal that could threaten them”, points out Laurane Winandy. “The second point is that fish are greedy animals that like to taste everything. Also, in this case this was done in a non-violent way - no newt was harmed – the fish tends to come into contact with the amphibians and to latch onto their skin with its mouth, as though it were giving then a peck. This is bound to disturb them. In addition, the sexual displays of male newts are very conspicuous and can also work as a lure. For example, the displays simulate the presence of food, which attracts the attention of females but which can also attract the fish and this can disturb the sexual display and eventually lead to its interruption”. Also, as the researcher goes on to remind us, these ‘exhibitions’ given by the male can last several minutes or even an hour, so the fish has plenty of opportunities to end them by making an untimely intervention.

Another important factor: when the female is receptive, the male may decide to deposit spermatophores which the female will either decide to use or not to use for reproduction. In many cases, she will not accept them and they will decay. If the fish eats these abandoned spermatophores, this will have no effect on the newts. On the other hand, if the fish seizes the spermatophores during the sexual display just after they have been deposited or while they are still attached to the female’s cloaca, this is detrimental to the reproduction process. This must surely be seen as one of the reasons for the heavy decline in the sexual activity of newts in the open unsheltered area of the aquarium.

When the number of sexual displays inside the shelter of each aquarium is counted, no difference is noticed between the control group (no fish) and the group where a fish was introduced. “Nevertheless, these figures are misleading”, indicates Laurane Winandy. “Because in the second group, the newts keep to the shelter more often than the newts in the control group (50% of the time versus 25%), which increases the probability of sexual displays in the shelter. If we consider the data in terms of establishing a relation between the number of sexual activities and the number of newts present, we can conclude that, even in the shelter, the newts engage in sexual displays less often when there is a fish in the aquarium. This signifies that the nearby presence of an intruder subjects them to general stress”.