Among life-history traits, immunity is an important fitness component that enables the defence of the organism from pathogens, i.e. helps ensure its survival. European crayfish species, keystone species of freshwater ecosystems, are especially vulnerable to oomycete pathogen Aphanomyces astaci.

Aphanomyces astaci, the crayfish plague pathogen, has caused the decimation of numerous populations of native European crayfish. It is known that this pathogen is carried by the invasive North American crayfish species, which are highly resistant to the pathogen. In contrast, European crayfish do not naturally carry the pathogen and are considered susceptible to the disease, potentially due to their comparatively lower expression of the prophenoloxidase (proPO), a key enzyme in the encapsulation of pathogens in melanin. Recently, however, resistant populations of native European crayfish, including the noble crayfish, have been detected throughout Europe. With our project, we aim to clarify the molecular effects of A. astaci infections on the crayfish, and to understand the response of the immune system of the vulnerable and protected native European noble crayfish. Results of this research will offer novel insights into the immune response of the noble crayfish to novel strains, with the emphasis on the strains isolated from latently infected crayfish populations in Croatia. Also, it will increase the understanding of the infection-immune activation process by examining in parallel the molecular effectors as well as changes in organs involved in the immune response.