This one is for you Jordan and Summer:
IntroductionAt BlizzCon we learnt that the Cataclysm would change the fishing "mechanic": Gnomish engineers would improve anglers' reels, and make better fishing poles. But another major fishing change is now expected in Cataclysm: The Aquarium.

Storing dead fish in bags or bank vaults is smelly. And nobody can see your rarest catches. Fish tanks allow anglers to keep their rarest catches alive - and gain rewards from doing so. They also let other people see precisely what rare fish you have caught!
The aquarium finally brings the best of "social fish-gaming" to Azeroth.
Aquarium UseAn aquarium can be purchased from Breanni (in Dalaran) or "Fishing Suppliers" across Azeroth, for 5g. Using the item will add a "Fish" tab to the "Pets" part of your character screen.
Add/remove rare fish, or items of scenery, by dragging the items between your bags (inventory) and the lower panel on the Fish tab. Only uncommon (green) or better quality fish can live in your tank. Fish caught before Cataclysm can be placed in the aquarium if they have not been used. For example, a Sea Turtle that you have already learnt to ride, cannot be added.
The Fish tab also allows you to:
* Feed: Feed your fish Stranglekelp from your inventory.
* Clean: Change your aquarium's water. You must be near a source of water.
* Show: Assemble your aquarium so everyone else can see it. 5 minute cooldown.
Fish Growth and DecayYour fish will grow if you provide enough food and keep your aquarium clean. An aquarium fish with a green-tinted icon is currently well-fed and growing. Fish in your tank grow in "stages". Without bonuses to growth (see below), the first growth stage takes 2 weeks. Later stages take twice as long as the previous growth stage: 4 weeks, 8 weeks, and so on, until the dwarves lose count.
Fish in your aquarium will start to "decay" if you forget to feed them. Or you don't change the water each week. A fish with a red-tinted icon is currently decaying and should be fed (and/or watered). Fish decay twice as fast than they grow. If a fish decays below its starting size, it dies. You will have to catch another fish and start again.
To grow fish, and gain rewards, you must feed and clean regularly!
Feeding and Cleaning
Fish should be fed daily. The fish in your tank eat Stranglekelp. You must feed 1 herb per fish, each day. Add Stranglekelp to the aquarium using the "Feed" button.
Your aquarium's water must be changed at least every 7 days. Travel to any area of open water (coastal or inland), click "Clean", and wait 30 seconds for the cast-bar to complete. Alternatively, you can use one of several special waters:
* Abyssal Water - Fill your fish tank from the altar in the Abyssal Maw (requires level 81 or above). Increases fish growth rate by 10% (non-Heroic) or 20% (Heroic).
* Brewfest Beer - Clean the aquarium while standing next to a Brewfest Pony Keg. Reduces fish decay rate by 25%.
* Moonwell Water - Clean your tank while standing in a Moonwell. Makes your fish shine and sparkle.
Aquarium ScenerySeveral items can be placed in your aquarium as scenery. These items are not consumed, and can be removed from the tank at any time. Scenery in your aquarium will help your fish survive or grow. For example:
* Dustbringer - Reduces fish decay rate by 30%.
* The 1 Ring - Random chance of growing a fish by one stage.
Expect to catch other items of scenery while fishing. Or find them sold from stores, via the Trading Card Game, alongside actual goldfish, in promotions for Rumsey Rum Black Label, or through any number of enterprising Goblin sales techniques. You'll be amazed how much space there is inside in your aquarium for more stuff!
RewardsEach stage of fish growth grants a reward. These rewards are bound to the owner of the aquarium, and cannot be traded. Most rewards are still unknown, but one example has been discovered by dwarven data miners (thanks Bibi):
Mr. Pinchy
* Mr. Pinchy - Every growth stage grants a new wish:
* Stage 1: Grants a "Brunch Box" (presumably containing food).
* Stage 2: "The Complete Guide to Dingo Dash" - vendors for 10g.
* Stage 3: "Mr. Pinchy's Birdinator" - gun that casts an area-of-effect fear spell on critters.
* Stage 4: Mr. Pinchy becomes epic quality, and can now be served as a feast. Eat for a "Hot Bath" buff, which grants +110 Fire Resistance (likely to be useful against Deathwing).
The Sea Turtle will also grow, gradually improving the Turtle's swim speed - eventually reaching 310% swim speed. The Sunken City of Vashj'ir is entirely underwater, so an "ultra-fast" turtle could be very useful. And will only take half a year of flawless fish-feeding to gain...
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So everyone grab their fishing poles! GO GO GO!