During breeding, some oriental river prawns ( Macrobrachium nipponense , de Haan), an important aquaculture species in China, exhibit yellowish‐brown body colouration, reduced appetite, and vitality. Diseased prawns revealed characteristic emulsifying disease signs, including whitened musculature, hepatopancreatic tissues, milky haemolymph, and non‐coagulation. The present study investigated the causative agent of M. nipponens...