Deep sea fish
Description of Niche
While the concept of deep sea fish may be a bit variable in terms of the depth they inhabit, it is usually understood that deep sea fishes are those living in the bathypelagic, abyssopelagic and demersal zone. Bathypelagic species, such as the angler fishes, inhabit the deeper part of the pelagic zone, lives from from 1,000 m down to around 4,000 m, while abyssopelagic species live from 4,000 m down to above the ocean floor. Demersal species occupy the bottom of the ocean floor and are divided into benthic and benthopelagic species. Benthic fishes are those that spend most of their time on the bottom such as the rays and flatfishes, while benthopelgic fishes are those that swim habitually near the ocean floor such as the squalid sharks (family Squalidae) and smoothheads (family Alepocephalidae).
The conditions of the deep sea are extreme and the species inhabiting the area are challenged with adapting to these conditions. The most challenging is perhaps the high hydrostatic pressure. For each 10m increase in depth, the pressure increases by 1atm (~0.101MPa). The average pressure below 1000m is near 380atm while the maximum may reach up to 1100atm. In addition to the high pressure, the temperature in deep sea is very low, typically in the range of 2-4°C. Lack of sunlight is another condition these animals are challenged with affecting their vision as well as the photosynthetic production below ~100m. Due to these extreme conditions, the deep sea species are expected to possess well adapted biochemical systems. Also, for the same reason, the bacteria that inhabit the organs of these species are mostly extremophiles such as barophiles and psychrophiles.
Influence of adjacent communities?
Hydrothermal vent is one community that may influence deep sea fishes. Although the water temperatures of hydrothermal vents are near 400°C, this area is very productive biologically hosting communities such as chemosynthetic archaea. Because of its high temperature and toxicity of its fluid, deep sea fishes adapted to the cold temperature may not survive around this community.