![Making the impossible possible – Tracking under water in the dark tracking-glass-eels](https://www.noldus.com/static/images/core-blog/tracking-glass-eels.jpg)
Making the impossible possible – Tracking under water in the dark
European eels (Anguilla anguilla) have a life cycle in which both larvae and adults travel incredible distances. The eggs hatch in the Sargasso Sea near North America and the larvae swim all the way to Europe.
![To mate or not to mate? Females are less choosy when males are rare fish-mating-preference](https://www.noldus.com/static/images/core-blog/fish-mating-preference-1572599012.jpg)
To mate or not to mate? Females are less choosy when males are rare
Having a choice for a mating partner is extremely important for females, so they can be critical in choosing which male to mate with.
![Zebrafish research: behavioral differences between wild-type strains zebrafish-behavioral-differences](https://www.noldus.com/static/images/core-blog/zebrafish-behavioral-differences-1581603163.jpg)
Zebrafish research: behavioral differences between wild-type strains
Often in animal research, animals with a certain genetic alteration are compared to a “wild-type”. One might assume that there is no differences between wild-types, but many different strains of wild-type animals are used.