Great Zapfish

The Great Zapfish is the main subject of and  single-player modes, Octo Valley and Octo Canyon. It is an extremely large Zapfish that powers all of Inkopolis.

Appearance
Unlike other Zapfish, the Great Zapfish is massive and more similar to the real-life electric catfish. It has yellow curled whiskers that give off electricity, an orange mouth, a peach face, a dark blue body, a small, dark blue tail with lime green along the edges, and similarly colored fins.

Splatoon


The Great Zapfish is a giant animal circling Inkopolis Tower, powering the city. According to the first Sunken Scroll, the Great Zapfish is 100 years old, and powers the entirety of Inkopolis. However, when the player enters Inkopolis Plaza for the first time, an Inkopolis News broadcast states that the Great Zapfish has been stolen, and that this event is believed to be linked to the UFO that crashed earlier outside of the city. When the player goes to Octo Valley for the first time, Cap'n Cuttlefish, a veteran of the Great Turf War from 100 years earlier, tells the player that the Great Zapfish has been stolen by the Octarians as an act of revenge for losing the war. Cuttlefish recruits the player so that they can take back the Great Zapfish, but first, the player must take back every regular Zapfish, as these were stolen as well in order to power the Octarians' underground domes.

After collecting all regular Zapfish, the player finds the Great Zapfish in the possession of DJ Octavio, leader of the Octarians, who baits the player into saving it before sucking it up into his Great Octoweapon, the Octobot King. After the player defeats Octavio with the help of Agent 1 and Agent 2, the Great Zapfish is saved and can be found resting on Inkopolis Tower for the rest of the game.

The Great Zapfish makes a cameo appearance in the stage Piranha Pit, where it occasionally rises from the water in the background. Embroidery depicting the Great Zapfish also appears as decoration on the Zapfish Satin Jacket.

Splatoon 2
As the player enters Inkopolis Square for the first time, an Inkopolis News report is cast by Pearl and Marina informing everyone that both the Great Zapfish and Callie have gone missing. After the player goes to Octo Canyon for the first time, Marie explains that Callie and the Great Zapfish have been taken by the Octarians. The player is given the Hero Suit and joins the New Squidbeak Splatoon as Agent 4. The player goes through a series of levels, obtaining both regular and mini Zapfishes along the way. After completing all levels, the player must defeat DJ Octavio in a final boss fight. With the help of Sheldon and Marie, the player defeats DJ Octavio and saves Callie and the Great Zapfish. After the player defeats DJ Octavio, the Great Zapfish does not return to Inkopolis Tower, but will instead be resting on Deca Tower or on the tracks above Grizzco, or even flying around the sky, producing a barely-audible jingle (the same jingle that plays in the final level of Octo Canyon, Tide Goes Out, when DJ Octavio is taking the Great Zapfish into the Octobot King).

The Great Zapfish also appears in Piranha Pit and on the Zapfish Satin Jacket just like in the first game.

Trivia

 * After the Splatoon 2 version update, many players reported the Great Zapfish missing in Inkopolis Square, even if they had already completed story mode. This was patched in a later update.
 * In WarioWare, Inc.: Mega Microgame$!, there is a minigame called Electric Groove Fish that has an electric catfish move electricity to the city to power it, similar to the Great Zapfish's role.