The skin is the largest organ that is exposed to the external environment and it functions to protect an animal from external insults. Exposure to the external environment makes the skin available to colonization by microbes that are found in any particular environment. This lends itself to great variations in microbial diversity of the skin externa even among animals of the same species as these microbial communities may adapt to changing environments. Unlike terrestrial animals, fishes are unique in that they live in an intimate relationship with their aquatic environment, which may directly and continuously transmit microbes across the entirety of their skin. Living in water has physiological advantages, such as moderation in temperature changes and an increased density of the environmental medium compared to air, however fishes may interact with a wide variety of microbes throughout the day depending on water flow, currents, or how much they move or migrate through their environment. This leads to an extensive diversity of microbes that a fish may directly encounter during their lives. This also makes them vulnerable to an extensive array of potentially pathogenic microbes. A greater knowledge of the skin microbial communities on fishes has the potential to increase our understanding of how fish interact with their environments and how the microbial communities may influence the immune functions of the fish.