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That's most likely his lateral line. All fish have them. They help the fish feel water movements so they can tell if something is sneaking up on them. My goldfish's lateral line just showed up one day and stayed like that. As for the bouyancy problem, goldfish are gluttons, and sometimes mine would swallow some air or tiny pieces of gravel and it would mess up his balance.
I hate hearing people say "it's only a $3/$5/$1 fish/shrimp, so it's ok if it dies, I can just get another." It's still an animal! All animals should be treated like they're worth $10,000.
29 sw: Damsel, shrimpgoby, pistol shrimp, waspfish
65 fw: Rummies, glowlight tetras, pencilfish, darters, ottos, f betta, goby, dwarf gourami, ninjas
29 fw: Chili rasboras, pygmy cories, P. Gertrudae