Timing and quantifying Aphanomyces astaci sporulation from the noble crayfish suffering from the crayfish plague

Aphanomyces astaci sporulation is crucial for the spreading potential of this disease agent. For the first time, we are reporting timing and quantity of A. astaci spores released from noble crayfish (Astacus astacus) suffering from crayfish plague under practical aquatic conditions. We infected nine noble crayfish with A. astaci PsI-genotype and maintained them in individual 8 L tanks. Spores (zoospores and cysts) were quantified from water samples (3 × 1 mL) taken every 12 h over 10 d using A. astaci specific qPCR. A clear sporulation trend was found, together with a high individual spore estimate variation. The median spore counts from two days before death to 12 h post mortem were from ∼500 to ∼2000 spores L−1. A significant sporulation increase occurred after 24 h post mortem (∼12,000 spores L−1) and reached a peak after two days (∼65,000 spores L−1) before declining to or below pre mortem levels from the fourth day. The single most sporulating crayfish released from ∼75,000 to ∼400,000 spores L−1 during the mass sporulating period, yielding a maximum estimate of ∼3,200,000 spores released from a single crayfish if we assume homogeneous spore distribution. The results confirm a mass A. astaci spore release from moribund and recently dead infected noble crayfish, with a sporulation peak one to three days post mortem. The acute crayfish mortality only three days after zoospore exposure confirm the lethal potential of the PsI-genotype. The powerful sporulation potential observed here may be one of the key virulence factors of this genotype