Mucosal Barrier Functions of Fish under Changing Environmental Conditions

Abstract

The skin, gills, and gut are the most extensively studied mucosal organs in fish. These mucosal structures provide the intimate interface between the internal and external milieus and serve as the indispensable first line of defense. They have highly diverse physiological functions. Their role in defense can be highlighted in three shared similarities: their microanatomical structures that serve as the physical barrier and hold the immune cells and the effector molecules; the mucus layer, also a physical barrier, contains an array of potent bioactive molecules; and the resident microbiota. Mucosal surfaces are responsive and plastic to the different changes in the aquatic environment. The direct interaction of the mucosa with the environment offers some important information on both the physiological status of the host and the conditions of the aquatic environment. Increasing attention has been directed to these features in the last year, particularly on how to improve the overall health of the fish through manipulation of mucosal functions and on how the changes in the mucosa, in response to varying environmental factors, can be harnessed to improve husbandry. In this short review, we highlight the current knowledge on how mucosal surfaces respond to various environmental factors relevant to aquaculture and how they may be exploited in fostering sustainable fish farming practices, especially in controlled aquaculture environments.

Effects of Water Acidification on Senegalese Sole Solea senegalensis Health Status and Metabolic Rate: Implications for Immune Responses and Energy Use

“…of acute hypercapnia exposure also on the external mucosal barrier. Mucosal surfaces (i.e., skin, gills and gut) provide fish the first line of defense, and skin mucus, similarly to peripheral blood, is armed with potent molecules, including lysozymes, complement proteins, lectins and antimicrobial peptides with important immune roles (Cabillon and Lazado, 2019). In this study, the modulation of humoral parameters found both in skin mucus and plasma seem to suggest some degree of adjustment to the acidic ambient water, even after a short period.…”

Effect of Light–Dark Cycle on Skin Mucosal Immune Activities of Gilthead Seabream (Sparus aurata) and European Sea Bass (Dicentrarchus labrax)

“…Regarding fish immunity, several studies have demonstrated the relationship between photoperiod and the immune system [8,9,12,15,31]. For example, a study conducted by our group (also on gilthead seabream and European sea bass) reported how the photoperiod affected some seric immune parameters (natural hemolytic complement, lysozyme and peroxidase activities) [8].…”

“…In this sense, it has been demonstrated that some components of the fish immune system also exhibit daily variations [8,12], but, to the best of our knowledge, the available information on this topic is very limited because such information mostly focus on seasonal variations (reviewed by [2]). In the above studies, daily rhythmicity was demonstrated in several components of fish humoral (such as complement, lysozyme, and peroxidase activities and globulin level) and cellular (leucocyte phagocytosis and production of reactive oxygen species) immunity [12,15,16]. Our group evaluated the effects of photoperiod on some seric immune parameters of gilthead seabream (S. aurata L.) and European sea bass (D. labrax) specimens [8], which are the most widely farmed fish species in the world [14].…”

The 1st international symposium on mucosal health in aquaculture – MHA2019

“…Fish have an intimate interaction with their immediate environment, where several challenges present themselves, including biological (e.g., parasites, bacteria, viruses), chemical (e.g., pollutants, therapeutics), and physical (e.g., handling sorting in commercial production). 1 These challenges put significant pressure on the adaptive and protective strategies of fish. The gills, skin, gut, and nasal mucosa are the major mucosal organs in fish, and they represent the interface between the internal and the external environments.…”