Alternatively, chemical exposures can stimulate the immune system leading to autoimmunity or hypersensitivity.In some cases, these effects may occur at concentrations well below thresholds for acute or chronic toxicity.Though immunotoxicity can affect all species, fish may be particularly vulnerable given their direct and constant interaction with water, a medium that is prone to contamination by a broad range of chemical classes and can harbour pathogens such as bacteria, viruses, and parasites.As such, the assessment of immunotoxicity in fish has become increasingly important for the protection of both cultured and wild populations.The importance of this work is underscored by the ecosystem, economic, and cultural services provided by fish (Holmlund and Hammer 1999).Fish are key components of food webs, regulate nutrient recycling and substrate distribution, and contribute to ecosystem resilience and diversity.From a cultural and economic perspective, fish represent a vital nutrient source as they provide 17% of animal protein intake globally, represent over $51 billion in international trade value annually, and provide recreational opportunities for 200-700 million people annually (Food and Agriculture Organization 2020).Furthermore, the fisheries sector promotes socioeconomic growth, reduces poverty, and improves the living conditions of vulnerable communities (Chan et al., 2019).Thus, mortality events due to infectious diseases in both captive and wild populations can have severe ecological, economic, and cultural consequences (Lafferty et al., 2015;Kataoka and Kashiwada, 2021).Fish are also useful surrogates for predicting the impacts of chemical exposures on other vertebrate organisms.Their immunotoxic responses can enhance our ability to predict chemical exposure impacts on immune function across a wide range of vertebrate taxa.Hence, understanding the role of toxicants and other environmental stressors on immune system function is necessary to develop effective management approaches that not only enhance the