La fauna abisal o fauna abisopelágica hace referencia a todos aquellos animales que habitan en las profundidades abisales de los mares y océanos, la zona abisopelágica o zona abisal es uno de los niveles en los que está dividido el océano según su profundidad, está situada por debajo de la zona batipelágica y por encima de la hadopelágica y corresponde al espacio oceánico entre 3.000 y 6.000 metros de profundidad. Son ciertas especies de animales marinos que nadan libremente, viven y se alimentan en aguas abiertas a dichas profundidades y nunca se aproximan a la superficie, excepto algunas especies.Las insondables profundidades abisales albergan una curiosa fauna con una apariencia monstruosa en su mayor parte. Los animales descritos por los científicos son todavía unos auténticos desconocidos en cuanto a su comportamiento y se sospecha que tan solo se ha descubierto una pequeña parte por lo que cada año se descubren nuevas especies. La mayoría de esta fauna tiene una morfología que recuerda a la de los monstruos de leyendas y cuentos.

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Deep-sea fish are fish that live in the darkness below the sunlit surface waters, that is below the epipelagic or photic zone of the sea. The lanternfish is, by far, the most common deep-sea fish. Other deep sea fishes include the flashlight fish, cookiecutter shark, bristlemouths, anglerfish, viperfish, and some species of eelpout. Only about 2% of known marine species inhabit the pelagic environment. This means that they live in the water column as opposed to the benthic organisms that live in or on the sea floor. Deep-sea organisms generally inhabit bathypelagic (1000–4000m deep) and abyssopelagic (4000–6000m deep) zones. However, characteristics of deep-sea organisms, such as bioluminescence can be seen in the mesopelagic (200–1000m deep) zone as well. The mesopelagic zone is the disphotic zone, meaning light there is minimal but still measurable. The oxygen minimum layer exists somewhere between a depth of 700m and 1000m deep depending on the place in the ocean. This area is also where nutrients are most abundant. The bathypelagic and abyssopelagic zones are aphotic, meaning that no light penetrates this area of the ocean. These zones make up about 75% of the inhabitable ocean space. The epipelagic zone (0–200m) is the area where light penetrates the water and photosynthesis occurs. This is also known as the photic zone. Because this typically extends only a few hundred meters below the water, the deep sea, about 90% of the ocean volume, is in darkness. The deep sea is also an extremely hostile environment, with temperatures that rarely exceed 3 °C (37.4 °F) and fall as low as −1.8 °C (28.76 °F) (with the exception of hydrothermal vent ecosystems that can exceed 350 °C, or 662 °F), low oxygen levels, and pressures between 20 and 1,000 atmospheres (between 2 and 100 megapascals).

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