Explain why some fish can survive in very deep waters?

Anatomical adaptations specific to great depths

Deep-sea fish often have a soft and flexible body to better withstand the immense pressure without being crushed. Thanks to their often cartilaginous or poorly calcified skeleton, they avoid having their bones break under several hundred atmospheres. These animals have little to no swim bladder, allowing them to endure extreme pressure without the risk of internal implosion. Some abyssal fish also have muscles and organs adapted to function with very little oxygen, enabling them to survive in these resource-poor environments. Their eyes are generally very large or, conversely, almost nonexistent depending on the species; it all depends on whether they hunt by capturing the slightest glimmer or rely solely on touch and vibrations. Their teeth are ultra-sharp and enormous relative to their size, ideal for quickly seizing food, which is scarce at these depths.

Mechanisms of tolerance to extreme pressure

Fish that live in the depths have developed special proteins to stabilize their cells against immense pressures. These proteins act somewhat like internal reinforcements that prevent the cells from being crushed under the enormous pressure of their habitat. They also have cell membranes with adjusted structures, containing more specific lipids, allowing the cells to remain flexible and functional even at great depths. Another clever trick: they often use small molecules called osmolytes that protect their cells while keeping their internal balance stable. In short, their entire body is fine-tuned to calmly withstand conditions capable of crushing most other organisms.

Energy management and reduced metabolism

In depth, food becomes rare: the fish in these environments have therefore profoundly altered the way they manage their energy. Their trick? A very slow metabolism, conserving those precious calories. Instead of being active all the time, they spend most of their time motionless, drifting slightly in the darkness. Many have reduced musculature, atrophied organs, or a lightweight skeleton to limit energy expenditure. Their movements are therefore slow, calculated, and economical. This minimalist strategy allows abyssal fish to survive for long periods without any meals, an ideal adaptation in the depths where every morsel counts.

Hunting techniques and food strategies in the abyssal environment

In the abyss, food is scarce, so there's no question of wasting energy! Many fish use a passive approach: they remain still, allowing their prey to come to them rather than chasing after it. A famous example is the abyssal anglerfish, with its luminous lure on its head, a sort of flashlight that naively attracts curious small animals directly to its mouth! Others, like certain viperfish, take advantage of their oversized jaws to gulp down prey that is sometimes almost as big as themselves—it's better not to let a meal slip away. It's simple: at these depths, one must be patient, opportunistic, and well-equipped to survive.

Communication and bioluminescence at great depths

In the total darkness of the deep sea, some fish use bioluminescence, a capability to create their own light like small natural lamps. Often, they have special organs called photophores filled with luminescent bacteria or chemical substances capable of glowing. They use these light signals to attract their prey, deceive their predators, or locate partners for reproduction. Some fish also produce a quick and intense flash of light to scare off a predator and escape stealthily right afterward. Other species can blink or modulate their light somewhat like a coded language to communicate with each other in the complete silence of the abyssal depths.