Goldfish bowl is for the goldfish scooping contest it goes in your ranged slot and the super scoop goes into the ammo slot. It is used to catch goldfishes, you get them from the NPC vendors that sell the super scoops.
There is a Goldfish Set which is obtained from the SunBreeze Event while goldfish scooping. This item can then be crafted into a Goldfish Bowl to be used as a furnishing in your MogHouse. =)
maybe it is for the event coming up. the goldfish scooping will be reintroduced so maybe you will be able to have a goldfish or two in your MH. i am only speculating tho.
I still had my goldfish bowl and some super scoops left over from last year, so I decided to catch a bunch of goldfish while waiting for the event to start... I turned in 80 points for the "Other Mystery Box" and got a Goldfish Set o o It's Ex and says "This set contains all you need to keep your pet goldfish happy."
How do you get this item though? And has anyone figured out what the purpose is beyond making the aquarium? I mean is it to raise your own fish instead of actually fishing like one person suggested, or is it just to look neat and give you a pet since the mithra pets seem to want their freedom?