Photographs and observations from submersibles have established the presence of deep-sea fish living around hydrothermal vents, but the difficulty in sampling these mobile fish from submersibles has restricted studies about their biology and ecology. About 25 families of deep-sea fish have been observed at hydrothermal vents around the world, with some species appearing to be found only at hydrothermal vents, and others commonly being observed in the deep-sea worldwide. However it is difficult to determine if there are many endemic species at hydrothermal vents. Studies on the food habits of some deep-sea fish species have found that some types of sessile invertebrate in hydrothermal vent communities are important components in their diets. This suggests that there are predator-prey interactions between these fish and the hydrothermal vent fauna, and recent studies have indicated that predation by large mobile predators, such as fish and crabs, can influence the structure of hydrothermal vent communities directly and indirectly. Further studies are needed to clarify the species composition and ecology of fish associated with hydrothermal vents and to examine their influence on sessile chemosynthetic communities.