Once upon a time, there was a fish.

That is the story; the rest is detail.

The details begin – as far as anyone can tell – with the day he was born. For the benefit of the reader, I shall pass over the not-so-euphoric [I don't think the word "euphoric" fits here. Euphoria is a state that can be reached almost exclusively through drug usage and I don't believe I've seen many examples of this word being used in a different sense] scene of his birth. Rather, we shall begin [You've established a very conversational tone, which is an excellent thing, but I think that "shall begin" clashes a little bit with it. I'd advise "let's begin" instead] approximately twelve seconds after the fish was spat out into existence. [I like the way you used "spat" here]

Upon opening his beady little eyes and discovering the wonderful and troubling thing that is life, the fish quickly realized two things: one, he really should really learn how to swim, being a fish and all; second, he was, in fact, terrified of water. Upon the realization of the latter, the former immediately took care of itself, [Very intricate sentence building, ten points for you!] and the fish was off like a kite in a hurricane, rocketing out of the ocean and into the dry up-world. [I'm not sure if I like the expression up-world]

“That's better,” said the fish, glad to be free of the horrific dystopia [Again, not a word I would use. You mentioned that he's terrified of water, but dystopia simply means a bad place to live. Since you're already going for a light-hearted mood, I'd put something humourous in, like "watery hell"] from which he had emerged. “I shall live here, now, I think.”

It just so happens that a philosopher happened [You use "happens" and "happened" fairly closely to each other, I would revise this] to be sitting on the beach when the fish appeared. Being a monoglot, the philosopher had never spoken to a fish before, philosophized to himself that this would be as good a time as any to give it a try. [This sentence feels a little awkward. I recommend you fix the structure up, something along the lines of: "Being a monoglot and having never spoken to a fish before, he philosophized..."]

“Hullo,” said the philosopher to the fish.

“Hello,” replied the fish.

“Having a nice tanning, are we? I caution you, young fish, that you could develop skin dystrophy.”

“I'm not tanning,” said the fish. “I'm looking for a place to stay. I've left my home, you see.”

The philosopher twirled his long, slender mustache and pondered this scenario. This was certainly strange. [In my experience, stating "this is strange" when a strange event occurs dulls the effect of the event somewhat. I'd cut that sentence out] After all these years of never once speaking to a fish, he finally finds the courage [Courage? He was afraid to speak to fish before? I thought he just never had the chance to do so] to engage one in conversation and finds that it wants nothing more than decent lodgings.

“Well,” he said to the fish. “I suppose you could stay at my cottage. At least for a time.”

With that said, the fish and the philosopher became roommates. It was a little jarring at first, as the fish tended to hyperventilate any time a bottle of water was brought into the room. But the two slowly but surely grew on one another. Being something of a misanthropist, [I'm fairly certain that's not a word. The word you're thinking of is "misanthrope"] the philosopher found that he rather preferred the fish to actual people. And the fish, having never met or talked to anyone before, was more than satisfied with the philosopher's company.

They talked often, and long. One particularly confusing discussion happened to be concerning the importance of shiny things.

“They're valuable, you see,” said the philosopher. “Without shiny things, the world would stop spinning?” [That doesn't sound like a question. It looks like the question mark was there by accident]

“So value is measured in shiny things?” said the fish. To him, and every other fish, there was no such thing as the concept of value. At least, not yet.

“I suppose so, yes,” said the philosopher, and meant it. It should be noted that he was not a particularly good philosopher, which is why no one knows his name to this day. But the fish believed him, and always remembered their discussion of shiny things. [I didn't see anything particularly confusing about this conversation on neither the philosopher's behalf nor the fish's, kind of contradicting your claim that it was confusing]

The two bunked together for the next few years, sharing countless discussions and stories. The fish liked the philosopher, and the philosopher wouldn't mind admitting that he was quite fond of the fish. They were happy together, and shared many laughs and banters and Christmastimes.

Had this been a love story, that last paragraph would have ended with the words “happily ever after.” But this is not a love story; this is a story about life. This story, like every other story about life, ends with death.

Being mortal, and being old, the philosopher soon succumbed to the natural way of things. The fish, who had come to understand the concept of dying long ago, was greatly saddened by the loss of his only friend. Abandoning the cottage by the ocean, the fish finally returned to his home in the deep blue.

When he arrived home, he was asked many questions, most having to do with the biological inaccuracy of how he survived so many years outside the water. The fish told them many things, sharing the words and teachings of the philosopher for all to hear.

But it was in the meaning and worth of shiny things that his listeners loved the most. The word spread of the value of shiny things, and before long they were among the most sought-after treasures in all the ocean. The tales of shiny things passed down from generation to generation, son to son, and the legend only grew as time went on.

This is why, when you throw a hook into the water, the fish bite it. They're not trying to get at the worm or the cricket or the chewing gum you have so barbarically impaled upon it. They simply want the shiny thing because, to fish, shiny things are the greatest treasure of all.