Although aquaculture activity has experienced a great development during the last decades, infectious diseases are a limiting factor for further growth and sustainability, which can severely impact socio‐economic development in many countries. Given that aquaculture usually requires large‐scale production facilities, animals are constantly exposed to stressful conditions, providing an ideal environment for the emergence (or re‐emergence) and spread of diseases of diverse aetiology. Moreover, this situation can be exacerbated by several interconnected factors such as the increased globalization of trade in live aquatic animals and their products; the intensification of aquaculture through the translocation of broodstock, postlarvae, fry and fingerlings; and the development and expansion of the ornamental fish trade, just to name a few. Therefore, investigation of the mechanisms and factors underlying infectious diseases in farmed fish and shellfish species is greatly needed to implement the effective control strategies.

This Special Issue of Journal of Applied Microbiology is dedicated to the understanding of several fish and shellfish diseases, including review and research articles on the latest advances in the aetiology and pathogenesis of such diseases, as well as suitable strategies to prevent their occurrence. The Special Issue is divided into two sections. The first one focuses on viral and bacterial diseases, which includes both a review of two important viral diseases caused by the Infectious Salmon Anaemia virus and the koi herpesvirus, and six articles on bacterial diseases. These latter include a review of iron uptake mechanisms as key virulence factors in bacterial pathogens, whereas the remaining five provide insights into pathogenic aspects of Streptococcus agalactiae , Photobacterium sp. and Vibrio sp. Because the use of antimicrobial agents has led to the emergence and spread of antimicrobial resistance, the search for alternative approaches is urgently required. The second section, therefore, focuses on environmentally friendly approaches for preventing and controlling diseases. In this section, six articles highlight the use of probiotics and prebiotic substances, three of them being about the advantages and shortcomings of probiotics used in aquaculture and three articles about the effect of several natural substances on the health, growth rate and application to fish and shellfish farming.

We believe that the collection of articles included in this Special Issue will provide new perspectives on the study of fish and shellfish diseases in aquaculture. We would like to sincerely thank all the authors in this issue for sharing their work and insights, as well as the reviewers for their suggestions.

尽管在过去的几十年中水产养殖活动取得了长足的发展，但传染病仍是进一步增长和可持续发展的限制因素，这可能严重影响许多国家的社会经济发展。鉴于水产养殖通常需要大规模的生产设施，因此动物不断受到压力条件的影响，为各种病因的疾病的发生（或再出现）和传播提供了理想的环境。此外，若干相互关联的因素可能加剧这种情况，例如活水生动物及其产品贸易的全球化日益加剧；通过亲鱼，幼体，鱼苗和鱼种的转移加强水产养殖；以及观赏鱼贸易的发展和扩大，仅举几例。因此，

《应用微生物学期刊》特刊致力于了解几种鱼类和贝类疾病，包括有关此类疾病的病因学和发病机理的最新进展的综述和研究文章，以及预防此类疾病发生的合适策略。特刊分为两个部分。第一篇着重于病毒和细菌性疾病，包括对由传染性鲑鱼贫血病毒和锦鲤疱疹病毒引起的两种重要病毒性疾病的综述，以及关于细菌性疾病的六篇文章。后者包括铁摄取机制作为细菌病原体中的关键毒力因子的综述，而其余五个提供了无乳链球菌的致病方面的见解，发光菌藻。和弧菌sp。由于使用抗菌剂已导致抗菌素耐药性的出现和扩散，因此迫切需要寻找替代方法。因此，第二部分着重于预防和控制疾病的环境友好方法。在本节中，有六篇文章重点介绍了益生菌和益生元物质的使用，其中三篇是关于在水产养殖中使用益生菌的优缺点，而三篇文章是关于几种天然物质对健康，生长率以及对鱼类和鱼类的影响贝类养殖。

我们相信，本期特刊中的文章收集将为水产养殖中鱼类和贝类疾病的研究提供新的视角。我们衷心感谢本期所有作者分享他们的工作和见解，以及审稿人的建议。