Aphotic zone - deep layers of water where sunlight does not penetrate.

From a... and the Greek phos (photos), light.

The deep water column of a body of water characterized by the complete absence of sunlight and almost complete absence of photosynthesis. It is formally defined as the depth beyond which less than 1% of sunlight penetrates. One of three ecological zones (along with euphotic zone and dysphotic zone), allocated in water bodies depending on the degree of illumination by sunlight and the presence of photosynthesis. Often this zone is also called the "night zone". It is characteristic of the open ocean, but can also be present in deep continental water bodies, for example, in Lake Baikal.

The aphotic zone is the largest zone of the open ocean (underlying the intermediate dysphotic zone), extending in the depth range of 1,000 - 11,000 m. It encompasses both the deep pelagial zones - bathypelagial, abyssopelagial and gadopelagial - and the deep ocean bed (benthali) zones - bathyal, pseudobathyal, thalassobathyal, abyssal, pseudoabyssal and ultraabyssal, or gadal. Compared to the euphotic and dysphotic zones, it is extremely poor, both in terms of biodiversity and biomass. Life forms - mainly predators and detritophages - exist here mainly at the expense of detritus, which is the so-called "corpse rain" of half-decomposed remains of hydrobionts falling from the overlying layers of the pelagial. The exception is a special deep-water ecological zone associated with black smokers - the hydrothermal zone with "oases of life" in which, in contrast to photosynthesis of the euphotic zone, the food chain exists due to primary production based on chemosynthesis of chemoautotrophic bacteria assimilating sulfide minerals of hydrothermal sources - hydrotherms.

The ichthyocene of the aphotic zone is represented by pelagic and benthic - near-bottom fishes, including groups of bathypelagic, bathybenthic, thalassobatibenthic, abyssobenthic and gadobenthic fishes.