Bolt & Float

This unnamed male Seashocker first appeared in Shock and Awe. He was befriended by Fishlegs.

Entrapment and Freedom
In "Shock and Awe", the Seashocker was separated from his pod and ended up in a lagoon. Fishlegs was eager to study the dragon and barricaded the lagoon entrance with Meatlug's lava blasts. After Fishlegs brought Hiccup and the other Dragon Riders to the lagoon, however, the Seashocker became agitated after a while and attempted to escape his confinements. As Hiccup and the others started to destroy the barricaded lagoon entrance, Fishlegs befriended the Seashocker.

When Fishlegs tried to let the Seashocker escape the lagoon, a pack of Scauldrons arrived after being drawn in from the explosions caused by the Dragon rider's dragons. After a lengthy chase and the Dragon riders distracting the Scauldrons, the Seashocker managed to escape. However, more Scauldrons arrived. Luckily, Fishlegs rescued the Seashocker by jumping on his back and joining his two heads together, creating a powerful electric field that knocked back the Scauldrons. Afterwards, the Seashocker reunites with his pod.

Trivia

 * In cronological order, he is the first Seashocker seen.