Short-term artificial incubation before hatching limits vertical transmission of Aphanomyces astaci from chronically infected females of a host species susceptible to crayfish plague
Abstract
Crayfish plague, caused by the oomycete Aphanomyces astaci and spread primarily by its original crayfish hosts from North America, not only threatens populations of endangered crayfish but also impacts their fisheries and aquaculture. This includes the narrow-clawed crayfish (Pontastacus leptodactylus) in Turkey, where its fishery and export used to grow until the mid-1980s when the accidental introduction of crayfish plague caused stock col-lapses.
Although crayfish densities in some Turkish lakes returned to levels where fishery is feasible, persistent chronic infections by A. astaci prevent full crayfish population recovery and stock exploitation. The establish-ment of closed culturing systems faces the problem of substantial mortality of both broodstock and juveniles originating from the wild, apparently associated with the stress-induced development of crayfish plague symp-toms.
In our experiment, we evaluated whether A. astaci is vertically transmitted to juveniles during maternal incubation, and to what extent hatching of crayfish eggs in artificial conditions, coupled with antifungal baths, limits the infection by this pathogen. Egg-carrying (berried) crayfish females were caught from the Lake Egirdir, Turkey, shortly before juvenile hatching.
Eggs stripped from females were assigned into four experimental groups: two groups were treated with antifungal baths (formaldehyde or peracetic acid), the other two groups were controls kept without antifungal treatment but set up in conditions differing in the likelihood of accidental A. astaci transmission. Eggs on five berried females were kept for maternal incubation.
The results confirmed that nearly all wild-caught females tested for the presence of A. astaci DNA by quantitative PCR were infected, and A. astaci infections were frequently confirmed in the maternally incubated juveniles. In contrast, we did not confirm unambiguous A. astaci infection in any juvenile from eggs treated by antifungal baths and from one of the control groups, which were all kept on a strictly separated flow-through system.
However, juveniles from the control group on a recirculating system, in which also infected crayfish (e.g., maternal incubation group) were present, suffered elevated mortality, likely related to the accidental introduction of the pathogen that was confirmed in this treatment. The separation of the eggs from infected mothers before hatching apparently sub-stantially reduces pathogen vertical transmission, and combination with an antifungal treatment further in-creases juvenile survival.
Although it cannot be guaranteed that the juveniles that hatched and developed in artificial conditions are entirely A. astaci-free, the approach seems suitable for routine aquaculture applications in regions where chronic infections by this pathogen are widespread.