How does a fish perceive the world?

I’m reading What a Fish Knows: The Inner Lives of Our Underwater Cousins by Jonathan Balcombe. Why? Since you ask, I want to learn about fishes. 
This is a fascinating book. 

“What we casually refer to as ‘fish’ is in fact a collection of animals of fabulous diversity. According to FishBase—the largest and most often consulted online database on fishes—33249 species, in 564 families and 64 orders, had been described as of January 2016. That’s more than the combined total of all mammals, birds, reptiles, and amphibians. When we refer to ‘fish’ we are referring to 60% of all the known species on Earth with backbones.” (Part I) 

You can read this book to learn some basic facts about fishes. For example, almost all modern fishes are members of 1 of 2 major groups: bony fishes (salmons, herrings, basses, tunas, eels, flounders, goldfishes, carps, pikes, minnows...) and cartilaginous fishes (sharks, rays, skates, chimaeras…). 
The book is also full of weird facts, such as this: 

“On finding a female, males of some deep-sea anglerfish species latch their mouths onto her body and stay there for the remainder of their lives. It doesn’t matter much where they fix their bite on the female—it could be on her abdomen or her head—they eventually become fused to her. Many times smaller, the male resembles little more than a modified fin, living off her blood supply and fertilizing her intravenously. 1 female may end up with 3 or more males sprouting from her body like vestigial limbs. 
[…] It is estimated that female deep-sea anglerfishes occur at a density of about 1 per 800000 cubic meters (28 million cubic feet) of water, which means a male is searching for a football-size object in a darkened space about the volume of a football stadium. Thus, it is desperately hard for anglerfishes to find each other in the vast darkness of the abyss, making it wise to hang on to your partner if you find one. 
[…] In exchange for the male being the ultimate couch potato, the female never has to wonder where her mate is on a Saturday evening. It turns out that some males do indeed amount to little more than an appendage.” (ibid.)  

Or: 

“Baby flounders look like any other normal fish, swimming upright with 1 eye on each side. Then, in preparation for adult life, they undergo a bizarre transformation: 1 eye migrates to the other side of the face. It’s like facial reconstructive surgery, only in slow motion, and without scalpels and sutures. It isn’t even always slow. The entire migration takes just 5 days if you’re a starry flounder, and less than 1 day in some species. If a fish can have an awkward adolescence, this one qualifies.” (Part II) 

What? 
Here’s a photo: 

I hope Balcombe writes about rays, which have eyes on the upper side of their bodies and mouths on the other side. 
Now check this out: 

“Flashlight fishes—one of the few bioluminescent fishes generally not found in deep waters—take a more direct approach to illumination, using a multifunctional light consisting of a semi-circular organ just below each eye. This pair of organs contains luminescent bacteria whose continuously emitted light can be turned on and off by the fish using a muscular lid. […] Mated pairs of flashlight fishes maintain territories over a reef, and if an intruding flashlight fish approaches, the female of the pair will swim up and flash her light literally in the interloper’s face, as if to say ‘Get lost!’.” (ibid.) 

That’s cool. Here are some photos: 



Such fascinating facts. 
I’ve been enjoying this book also because I’m interested in how fishes perceive the world. Balcombe’s intention in writing the book, it seems, is to debunk myths, and to help people realise that fishes (he prefers this to “fish”) are a lot more complex, knowing, and interesting than we realise—they are sentient beings, with personalities and feelings. 
He writes about their sense and perceptions. Most fishes can see more colours than we do—they can see light in the near UV spectrum. Fishes can hear, some can hear ultrasounds, much above human limit, whilst some others are responsive to infrasounds as low as 1 Hz.  
Fishes can also create sounds: 

“Despite the common assumption that fishes are silent, they actually have more ways of producing sounds than any other group of vertebrate animals. None of these methods involve the main method of all the other vertebrates: the vibration of air against membranes. Fishes can rapidly contract a pair of vocal muscles to vibrate their swim bladder, which also serves as a sound amplifier. They have the options of grating their teeth in their jaws, grinding additional sets of teeth lining their throat, rubbing bones together, stridulating their gill covers, and even—as we’ll see—expelling bubbles from their anuses.” (ibid.) 

The descriptors human beings have assigned to fishes’ symphony of sounds are: “hums, whistles, thumps, stridulations, creaks, grunts, pops, croaks, pulses, drums, knocks, purrs, brrrs, clicks, moans, chirps, buzzes, growls, and snaps.” (ibid.) 
Not only so, fishes fall for optical illusions like humans, which means that they perceive things and form mental concepts instead of perceiving visual fields in a mindless, mechanical way, like robots.  
They also know more than we think they do—they can be trained, and as shown in a study, can distinguish between different music genres. 
I’m afraid that after reading this book, I can’t eat fish again. I love salmon.