The nutria (Myocastor coypus) is a medium-sized semi-aquatic rodent, which is native to South-America, but it has also been introduced to several other parts of the world as well. For example, it has become widespread in Central Europe. In Slovakia, nutrias were kept for fur and meat production, which historically dates back to the 1920’s. Some of these animals escaped, others were released after the bankruptcy of nutria-based fur industry. Established populations of wild nutria have a number of harmful activities, such as deterioration of water management structures, damage to agriculture, etc.

Our aim is to study this animal in Slovakia and answer the following questions:

• Are the female and male individuals well-developed in the wild and in good condition for reproduction?
• How intensively does the species reproduce in this non-native area?

We collected our samples by trapping and hunting in differrent seasons, then the carcasses were investigated in the laboratory.

Our results showed that the animals were in good condition. Meanwhile the adult specimens were bigger than the juveniles, the males’ and females’ body sizes were not significantly different (body weight, body mass and body length index). We concluded that the nutria can be highly reproductive, as the average number of embryos in pregnant females was 6.6±2.1. From March to October 70% of females (11 of 12 adults and 3 of 8 juveniles) were pregnant, and we found a specimen with 10 embryos even in October.

The nutria is able to reproduce and spread rapidly in the introduced areas, potentially leading to adverse environmental or economic effects. Therefore, an urgent intervention is needed to stop their expansion, and possibly eradicate them.