The ocean is home to tens of thousands of fish． You can see fish swimming freely in the water． But you may not know that fish cannot explore every part of the ocean．

Recent studies have found that the deepest depth（深度）a fish can swim is 8，200 meters．（1） 　 　This is because of a chemical（化学物质）in fishes' cells（细胞）that is called Trimethylamine N﹣oxide（TMAO）．

For example，if you take a ping﹣pong bal 10 meters underwater，the pressure turns it into a tiny piece of plastic．（2） 　 　TMAO warns fish of this danger at about 8，200 meters． If fish swim deeper，the TMAO chemical stops working and starts to damage（破坏）the fishes' brain cells．

Although there is life at the bottom of the sea，most fish live within （在……范围内）the top 1，000 meters of the ocean．（3） 　 　

（4） 　 　The anglerfish is one such fish． It lives about 2，000 meters deep in the ocean． There is no sunlight at this depth．（5） 　 　They use the light to find food． Below even these fish is the cusk﹣eel． These small fish live close to the ocean floor at a depth of 8，000 meters，far out of reach of hungry predators（猎食者）．

A． But anglerfish can produce light themselves． B． This is about three quarters of the depth of the deepest part of the ocean． C． Deeper down in the ocean，the most dangerous animals are the deep﹣sea fish． D． Most things break down after a certain depth underwater because of the high pressure． E． Even sharks，the "kings of the ocean"，have never swum deeper than 4，000 meters．