Fish

Fish are a collectible item in Mass Effect 2 and Mass Effect 3. In Commander Shepard's personal cabin on the Normandy SR-2, there is a large aquarium on the left side of the cabin which can be filled with fish. There are three types of fish available and the stores that sell them will restock after every purchase. Rearing fish does not have any benefits except as an aesthetic feature for Shepard's cabin; story and gameplay are unaffected.

Care
Just as it is necessary with real fish, Shepard's piscine companions must be fed after every mission or assignment to ensure that they remain alive. Otherwise, Shepard must clean out the dead fish and purchase new ones. If Shepard has flirted with Kelly Chambers and invited her to dinner, the option to have her feed the fish will become available.

In Mass Effect 3, Shepard can purchase an upgrade module for fish tank that will automatically feed and care for the fish. The Aquarium VI is available for purchase at the Elkoss Combine Arsenal Supplies terminal in the Presidium Commons of the Citadel for 25,000 credits.

In addition, if Kelly Chambers survived the Suicide Mission, was taking care of Shepard's fish, and the fish survived as well, when the Normandy was impounded, Kelly saved Shepard's fish by taking them with her and she'll return them to the Commander once they meet on the Citadel.

Mass Effect 2
* Only available after the mission on Horizon.

Mass Effect 3

 * Despite its description the Khar'shan Snapping Eel will not eat your other fish.
 * The Prejek Paddle Fish is available as well, but only if Kelly Chambers saves Shepard's fish from Mass Effect 2.

Trivia

 * While on the Citadel in Mass Effect 2, Shepard overhears a krogan named Kargesh wondering whether there are fish in the Presidium lakes. Similarly, while walking around on the Presidium in the first game, Wrex states that he is hungry, and asks if Shepard thinks there are any fish in the lake.
 * Due to its unusual means of movement and tendency to swim "racetrack" circles, the Prejek Paddle Fish frequently clips right through the aquarium walls, swimming freely around in the air of Shepard's cabin or going through the ceiling and floor of the tank, before drifting back into the aquarium. This usually happens right after feeding.
 * The fish tank in the Captain's Cabin office area on the Normandy might be a reference to Star Trek: The Next Generation, in which there is a fish tank in Captain Picard's ready room aboard the Enterprise-D.
 * In Lair of the Shadow Broker, Liara has a fish tank in her apartment. It contains all of the fish that Shepard can acquire, in addition to jellyfish-like creatures.
 * If you import a save from Mass Effect 2 with a live Prejek Paddlefish into Mass Effect 3 and keep the Paddlefish alive thorugh an entire Mass Effect 3 playthrough AND a Mass Effect 3 New Game+ playthrough you can get a special Intel Bonus from Liara's Quarters on the Normandy. The Prejek Paddlefish Bonus gives you a 10% bonus to either Weapon Damage or Power Damage.

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