Sixty percent of all the known species on Earth are fish. That’s 33,249 species to be exact — more than all the birds, reptiles and mammals combined. Yet the simple fact that fish live in an alien environment has created an information gap that scientists have been hard-pressed to bridge.

Until now.

Jonathan Balcombe, a professor of animal studies, fills the void in his new book “What a Fish Knows,” which argues we’re not as different from our water-brethren as you’d think.

Most fish don’t have memories that wipe clean every three seconds, like your uncle said when you worried about your goldfish in a bowl getting bored. In fact, fish were evolving at the same time as our anthropoid ancestors, and they’ve had an equal amount of time to become aware of their environments.

Although obviously lacking in opposable thumbs, fish have impressive jaws that developed more than 50 million years ago and allow the swimmers to communicate, manipulate objects and even carry their young.

“These behaviors suggest a being with a mind,” writes Balcombe.

Studies have shown that fish can learn some things better than our closest primate cousins. They are social creatures and some even live in social hierarchies. Many court prior to mating.

The frillfin goby can make mental maps of multiple tide pools when picking and choosing the one they want to hang out in during the next low tide. Goldfish assigned colored feeding tubes one year can still remember their assigned tube a year later.

The elephant fish and the knife fish use electricity to communicate. These fish use electronic signals to work together or send out early-warning alerts that a predator is lurking nearby and can even use these signals to convey emotions like aggression and submission.

‘[Fish] are individual beings whose lives have intrinsic value apart from any utilitarian value they might have for us.’ - Jonathan Balcombe

These species also use a kind of aquatic music to serenade perspective mates, which Balcombe refers to as “exotic patterns of chirps, rasps or creaks.”

On a less romantic note, both Pacific and Atlantic herring use what Balcombe calls, “flatulent communication,” a series of gas bubbles believed to convey important information. Scientists call them fast repetitive ticks, or FRTs for short.

Even facial recognition — often considered a higher form of cognition — is widespread among fish. They can decipher facial markings on other fish that humans can only see with the aid of a UV light.

Even more surprising are the number of anecdotal stories of fish recognizing individual humans — typically those who feed them. In one study of archerfish, Balcombe writes, the fish quickly learned to seek out the person who gave food rewards. They even have a superb sense of hearing — without needing ears (water is an excellent conductor of sound).

Karl von Frisch, an Austrian biologist famous for decoding the language of honey bees, conducted an experiment on a blind catfish. Every day, he whistled while placing food in a specific location in the tank. Soon von Frisch stopped handing out food and only whistled. The fish still went looking for the food on the audio cue alone.

Some fish, including sea horses and flounders, have eyes that rotate independently. The fact that these fish can process two visual fields consciously at the same time with a single brain might be tough for us lowly single-field processors to fathom.

But the real question is, do fish understand what they see the same way a human does? Do they see a rock or can they see a specific rock? Many believe they see like robots — as in, rock, sand, food, repeat.

Balcombe tested this assumption by giving redtail splitfins a series of optical illusions. Two identical discs of food were presented, each surrounded by circles — one framed by large circles, the other with small ones. To the human eye, the food surrounded by small circles looked bigger than the disc surrounded by large ones. Like the humans, the fish picked the food with smaller discs (i.e., bigger food).

“This result showed . . . that redtail splitfins do not perceive things in a mindless . . . way,” writes Balcombe. “Rather they form mental concepts — sometimes fallible ones — based on their perceptions.”

And yet fish are often, according to Balcombe, “relegated to the outer orbit. . .of [our] moral concern.”

Today, countries are enacting laws that protect the interests of fish, much like those protecting land-based species. Rome has prohibited the sale of spherical goldfish bowls, saying that the environment is “cruel” and does not offer enough oxygen. Switzerland enacted a law requiring anglers to take classes to learn how to fish humanely.

“[Fish] are individual beings whose lives have intrinsic value apart from any utilitarian value they might have for us,” writes Balcombe. “With the rise of reason, humanity is on a course toward a more inclusive, more enlightened era.”