What fish live in the great depths of the ocean? What characteristics do they have to survive there?

The oceans cover about 360 million square kilometers, or just over 70% of the Earth's surface with Lifeguard course. It is estimated that they contain in round numbers about 1,300 million cubic kilometers of water, which would indicate an average depth of about 3,600m. But, in reality, the ocean depths vary enormously due to the rugged relief of the seabed, with mountain ranges such as the ridge or ridge that runs from north to south through the middle of the Atlantic, and trenches, such as the Mariana Trench, in the Western Pacific, at the southern end of which is the deepest known point, about 11km from the surface (24% more than the height of Everest). In all that vast volume of water live fish, as well as other organisms, but their density decreases as you descend to the depths.

We speak of deep-sea fish:

To designate those that live more than 200m deep. Today its known species amount to between 6,000 and 8,000, that is, between 10 and 15% of the world's fish diversity, which is estimated at some 55,000 species. However, the waters in which they live have a volume more than one hundred times greater than that occupied by the rest of the planet's waters, although it is an inhospitable environment, with high pressure, low temperatures, very little food and total absence of light. It is not surprising, then, that deep-sea fish exhibit remarkable adaptations, resulting from millions of years of natural evolution, by which they manage to survive in this extreme environment.

Non-scale diagram of the ocean zones:



The area permanently covered by marine waters is called the pelagic zone and is divided into the neritic zone, which coincides with the continental shelf and the slope, and the oceanic zone, offshore from the former. A distinction is also made between the epipelagic or photic zone, in which sunlight penetrates, and the aphotic zone, in which it does not. Below the second, four others have been defined: the mesopelagic zone (between 200 and 1,000m deep), the bathypelagic zone (between 1,000 and 4,000m), the abyssopelagic zone (between 4,000 and 6,000m) and the hadalpelagic zone (beyond 6000m).

Among these adaptations:

Are photophores or luminescent organs, glands at the ends of which bacteria produce light through biochemical reactions. Likewise, some have sensory mechanisms to detect the pressure waves generated by other animals when swimming. In this way they manage to avoid predators, communicate with conspecifics and locate and attract both possible breeding pairs and prey.

The extreme ecological conditions of the ocean depths have favored evolution by convergence, that is, the appearance of similar anatomical and physiological structures in animals of different ancestral lines. For example, similarities are observed in the eyes of invertebrates that live in these depths, including squid, and vertebrate fish from the same environment. The adaptations that differentiate deep-ocean organisms from shallower-dwelling species encompass not only their morphology and physiology, but also their behavior.

Depending on the location of their habitat in the water column, deep-sea fish can be called mesopelagic if they live between 200 and 1000m, bathypelagic if they live between 1000 and 4000m, and abyssal if they live between 4000m. and the 6000m. Beyond 6000m, there is talk of hadal fish. If they live in association with the seabed they are called benthopelagic and if they are in direct contact with it, they are called benthic.



Some species

The Atlantic pit viper (Chauliodus Sloane) has an eel-shaped body covered in thick scales. It measures about 35cm long. Its dorsal fin, located in the front third of its upper part, has erectile anterior rays, which, when erect, allow the fish to appear larger in body. Its jaws, with long, sharp, sharp teeth, spread up and forward from the gills when it eats, while its heart and blood vessels spread down and back, an extreme mouth expansion that accommodates the passage of large prey. Its body is silvery blue, with intense iridescence on the back and flanks of the Lifeguard training miami usa.