The first fish-like creatures evolved 530 million years ago. Today, there are at least 31,800 species of bony fish, including bass, tuna, eels, goldfish, carp, and 1,300 species of cartilaginous fish in the form of sharks, rays, and skates. Fish are astute problem solvers, are social, and form bonds. They even recruit members of other species to hunt together. Most fish species lay eggs—with some exceptions bearing live young, including white sharks. Parental care for eggs and young is common and can be quite elaborate. Males tend to be the primary caregivers—in many species fasting for weeks so that their mouths can provide shelter for eggs and newborns. Even without vocal cords, fish have extensive and highly effective sound communication via gnashing teeth, hissing, whistling, grunting, moaning, and shrieking. Almost all fish species possess some form of electroreception — the biological capability to pick up electrical stimuli. It is used primarily to detect prey and avoid predators. Only fishes, bees, and cockroaches have this ability.

A Greenland shark is believed to be almost 400 years old, making it the longest-living vertebrate on Earth.

Between 1 trillion and 2.7 trillion fish are killed by commercial fishing every year. That does not include fish caught illegally, recreational fishing, bait fishing, bycatch fish caught in nets who die later, or fish used to feed shrimp and other fish in commercial operations, all of which add up to billions of additional fish killed every year.

Bycatch is devastating to non-targeted marine life. As ethologist Jonathan Balcombe puts it, “Try to visualize a pile of marine creatures weighing 200 million pounds, most of them dead, almost all doomed to die. That’s the daily bycatch we reap from the seas.” Alas, aquaculture (farmed fish) provides no relief to fishes: dense masses of fish are fed fast-growth-inducing feed made in large part from wild-caught fish from the sea. In fact, the majority of prey fish harvested from the oceans are fed to factory-farmed cattle, pigs, chickens, and fish—not humans.

The demands of the exploding human population have severely damaged aquatic ecosystems around the world through water consumption, river damming, introduced invasive marine species, and plastic and other water pollution. This destruction has caused at least 1,851 species (21% of all fish on Earth) to be at high risk of extinction, including 39% of all fish species in North America.