Research advances in the structure, function, and regulation of the gill barrier in teleost fish

The gill is an important organ in fish that is involved in various physiological functions, including respiration, filter-feeding, ammonia nitrogen excretion, and osmoregulation. The physiological functions of gills are closely related to their structure, external feeding conditions, and environmental factors. Herein, we first briefly summarize the basic structure and functions of the gills of teleosts, then explain the structure and function of the gill barrier (as a microbial barrier, a chemical barrier, a physical barrier, and an immune barrier) in detail. Finally, we introduce the regulation of fish gill barrier health by ubiquitous feeding factors and environmental factors, and provide an outlook on the prospects of gill barrier health. We found that improving health through modulating feed factors is more convenient than improving environmental factors. This review increases our understanding of how nutrient composition and level in fish diet influences gill health and overall growth performance of fish.