Centuries ago, an ancient water-dwelling race built a hidden city beneath a mountain in the sea. Though these creatures had their enemies, the city was an impenetrable fortress, and, in the safety it provided, they grew complacent. Fizz, however, harbored a curious spirit that could not be satisfied living so cushioned a life. Unable to resist the allure of danger, Fizz had a habit of sneaking out of the city to look for trouble. In his many adventures he grew to be a powerful fighter with a sharp cleverness that let him skirt danger with ease. One day Fizz returned to find the city abandoned: his people had vanished, leaving Fizz without a clue to explain their disappearance. With nothing left in the city to keep him, Fizz salvaged an enchanted seastone trident from the ruins and set out alone.

Fizz wandered the ocean in search of his people for years, using the skills he’d learned during his adventures as young boy to survive. Finally, Fizz discovered the port of Bilgewater. He was fascinated with the existence of life above the water and could not resist exploring the island. In his endless curiosity, Fizz inadvertently meddled in the affairs of the humans who lived there, and his presence did not go unnoticed. His mischief angered many residents who eventually sought to capture or kill him. Fizz found himself cornered, and he prepared to return to the sea despite the fondness he’d come to hold for Bilgewater. As he stood at the docks, a massive dragon-shark attacked the port. Fizz defeated the beast, using his resourcefulness and knowledge of the creature’s weaknesses to his advantage. Having earned the gratitude and respect of the humans, Fizz decided to stay in Bilgewater. To further serve his new home, he joined the League of Legends.

“Fizz makes even the saltiest sailors of Bilgewater look like drunken landlubbers in a fight. Good thing he’s on our side.” – Miss Fortune, the Bounty Hunter

For a tanky jungle, it's obvious to pick armor yellows. You can also pick armor / mr blues, that's pretty much up to you.
Attack damage quints & marks work pretty good, attack speed runes work just as fine though.

9/21/0, for defensive stats and also the little benefit from the extra attack damage and attack speed in offense.

Clotch armor + 5 pots is the best starting combo for fizz, 3 pots and boots is probably better if you're planning on invading the enemy jungle / ganking a lot in the first minutes. Obviously rush lantern as soon as you can. After lantern, tenacity boots.

You're going to build frozen mallet for health and the slow passive. Fizz benefits from frozen mallet really really good, can't really think of a better item for him.
After mallet, i recommend building atmas. It will give you some +50 attack damage when you buy it, and the extra armor is always good.

It's really up to you if you want to build warmog or wit's end first. Obviously warmog will give you really much health (and like 30 extra damage from atmas), but with wit's end your damage is pretty much doubled.

Smite for obvious reasons.

I recommend flash, but since you can escape situations with E, and if feel like playing it risky, pick ghost (or exhaust if you know they've got a really high damage carry in their team, like vayne / trynda).