LIFE OF THE DEEP SEA FISH

 

LIFE OF THE DEEP SEA FISH

 

 

Deep-sea fish are animals 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.

People have been fishing in the deep sea for over half a century. Over time, ever deeper ocean regions have become accessible to deep-sea fisheries. These hidden habitats are doubly endangered, because they are home to rare as well as sensitive organisms. Fortunately, the knowledge that these ecosystems require special protection is gradually becoming accepted.

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.[1] 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.[2]

 

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).[3]

In the nutrient-rich and highly productive coastal regions, massive reproduction is typical of many species, and this ensures their survival. Many deep-sea fish species, on the other hand, are characterized by slow growth, late sexual maturity, long life, and the production of fewer offspring. They are adapted to life at great depths, to a habitat in which unchanging environmental conditions prevail. The strong temperature fluctuations that can impact the reproduction of fish in shallow coastal regions are absent here. However, the deep sea is not as rich in nutrients as the coastal waters. The carrying capacity is almost exhausted and competition for food is great. Most species have therefore adapted by producing fewer, but highly competitive offspring. This reproduction strategy is called K-strategy (K refers to the carrying capacity of the environment). There is a high parental investment in the offspring. The eggs of many deep-sea fish are relatively large and rich in nutrients so that the larvae have a good chance of developing well.