An adequate sampling methodology is the key to knowing the health status of aquatic populations. Usually, the aims of epidemiological surveys in aquaculture are to detect an infection and estimate the disease prevalence, and different formulas are used to calculate the sample size. The main objective of this study was to assess if the sample sizes calculated using classical epidemiological formulas are valid considering the sampling methodology, the population size, and the spatial distribution of diseased animals in the population (non-clustered or clustered). However, the use of sample sizes of 30, 60, and 150 fish is widely accepted in aquaculture, due to the requirements of the World Organization for Animal Health (OIE) for epidemiological surveillance. We have developed a specific software using ASP (Active Server Pages) language and MySQL database in order to generate aquatic populations from 100 to 10 000 brown trouts infected by Aeromonas salmonicida with different levels of prevalence: 2, 5, 10, and 50%. Then we implemented several Monte Carlo simulations to estimate empirically the sample sizes corresponding to the different scenarios. Furthermore, we compared these results with the values calculated by classical formulas. We determined that simple random sampling was more accurate in detecting an infection, because it is independent of the distribution of infected animals in the population. However, if diseased animals are non-clustered it is more efficient to use systematic methods, even in the case of small populations. Finally, the formula to calculate sample size to estimate disease prevalence is not valid when the expected prevalence is far from 50%, and it is necessary to increase the sample size to reach the desired precision.

中文翻译：

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通过模拟技术评估水产养殖中使用的样本量计算。

适当的抽样方法是了解水生种群健康状况的关键。通常，水产养殖中流行病学调查的目的是检测感染并估计疾病的流行程度，并且使用不同的公式来计算样本量。这项研究的主要目的是评估使用经典流行病学公式计算的样本量是否有效，考虑了抽样方法，种群数量以及种群中（非聚类或成簇）患病动物的空间分布。但是，由于世界动物卫生组织（OIE）对流行病学监测的要求，在水产养殖中广泛使用30、60和150条鱼的样本量。我们已经开发出一种使用ASP（活动服务器页面）语言和MySQL数据库的特定软件，以便生成100到10000条被鲑鱼气单胞菌感染的鳟鱼的水生种群，其流行率分别为2％，5％，10％和50％。然后，我们实施了几个蒙特卡洛模拟，以根据经验估算与不同情况相对应的样本量。此外，我们将这些结果与经典公式计算的值进行了比较。我们确定简单的随机抽样可以更准确地检测出感染，因为它与种群中被感染动物的分布无关。但是，如果没有聚集患病的动物，则即使在人口少的情况下，使用系统的方法也会更有效。最后，