| Viral covert mortality disease (VCMD), caused by the covert mortality nodavirus (CMNV), is a highly prevalent viral infection affecting the majority of cultured shrimp. Shrimp suffering from this disease exhibit clinical hepatopancreatic atrophy and necrosis, empty stomachs and guts, soft shells, and slow growth. During the acute infection stage, infected shrimp display opaque abdominal muscles. Farmers have observed daily mortalities in the diseased population, with mortality rates increasing between 60-80 days post-stocking and reaching cumulative mortalities of up to 80%. Studies had confirmed that CMNV can infect major cultured crustaceans including Penaeus vannamei, P. chinensis, Marsupenaeus japonicus, P. monodon, and Macrobrachium rosenbergii. The prevalence of VCMD has resulted in significant economic losses within the shrimp farming industry over the past decade. Recognizing its widespread occurrence and substantial economic impact on Asian shrimp farming operations, VCMD has recently been acknowledged as a significant emerging disease in aquaculture by the World Organization for Animal Health (WOAH). The occurrence of VCMD is closely related to the factors such as whether the shrimp infected with CMNV, culture density and culture environment. After shrimp are infected with CMNV, the disease usually occurs when the water temperature is high and the environment changes sharply. However, accurately determining the extent to which each factor is associated with VCMD occurrence remains challenging. Therefore, this study aimed to assess the risk of VCMD occurrence during shrimp culture by establishing a comprehensive risk assessment framework using the Delphi method, Analytic Hierarchy Process (AHP), and Multiple Objective Comprehensive Evaluation (MOCE). The evaluation index system consisted of 1 target level (risk assessment and early warning of VCMD occurrence), 5 criteria layers (including health status, water quality and temperature, culture mode, culture management, and environmental status), and 20 indicator layers (including CMNV infection, soft shell, empty stomach of jejunum, opaque abdominal muscle, dissolved oxygen, ammonia nitrogen, nitrites, pH value, water temperature, factory culture, greenhouse culture, high-altitude tank culture, soil pond culture, breeding density, compound feed, chilled food, fresh food, surrounding disease, facility isolation, water treatment). The relative weight and absolute weight of each risk indicator in risk assessment framework of VCMD occurrence are calculated based on expert scoring results. And the total matrix consistency ratio is CR < 0.1, indicating that the overall consistency test passes successfully. Additionally, the matrix consistency ratios for each criterion layer are 0.0007, 0.0191, 0.0000, 0.0025, and 0 respectively; all of which pass the matrix consistency test as well. The weight values of 5 criterion-level risk factors were W= {0.420, 0.127 ,0.094 ,0.214 ,0.146}. The higher weight values of risk factors, including CMNV infection (0.1734), culture density (0.0946), opaque abdominal muscle (0.0859), and soft shell (0.0838), respectively, indicating that these factors might be crucial for the incidence of VCMD in shrimp culture. Then, it was preliminarily validated by studying the case of three shrimp farms located in Shandong province with methods of multiple objective comprehensive evaluation. The risk value of VCMD occurrence in these three shrimp farms were 0.54975, 0.50785, and 0.46595 respectively, all indicating a high risk of VCMD outbreak. Consistently, within four days after monitoring and sampling activities, severe cases of VCMD occurred in all three farms with a mortality rate exceeding 80%. These findings demonstrate that the risk assessment results align with the monitoring results and confirm the model"s accurate early warning capabilities for assessing the occurrence of VCMD. In summary, this study has established a convenient and feasible risk assessment model for the occurrence of VCMD in shrimp culture course. The risk assessment model comprehensively considers various factors that contribute to the occurrence of VCMD during the culture process, ensuring accurate assessment results. This research suggests that the proposed risk assessment model could be used to estimate the risk of VCMD occurrence in shrimp culture course, and serve as an early warning tool for prevention and control, thereby ensuring the healthy and sustainable development of shrimp farming. |
