UPDATE: More details have been released about the Arena Tournament. The Armored Murloc will be awarded to anyone participating in the minimum number of required matches on the tournament realm. Also, it looks like the pet will be bind-on-account, as it may be associated with characters on the player's account:
Each Eligible Participant that competes in two hundred (200) matches during the final four weeks of the Qualification round of the Tournament shall be eligible to receive a unique, in-game “pet,” that the Eligible Participant may associate with characters on the World of Warcraft account registered by the Eligible Participant. The pet will be mailed to the character designated by the Eligible Participant during the registration process within four weeks following the Qualification Round of the Tournament.
Registration is now open for North America and Europe. Good luck!