From CScout Japan:

"...this restaurant** in Japan has a goldfish tank…in the deep fryer. Because oil floats on water, despite the massive heat (163 degrees Celsius) the goldfish simply stay away from the surface and all is well. They eat the crumbs of croquettes and other fried foods that fall to the bottom, and can live in there for 5-10 years** as they happily clean away, ignorant to the fact that certain death awaits any potential escapees.This one is hidden away back in the kitchen where customers can’t even see it, but it could easily be made for display near the dining area for everyone to see. No word on whether they turn cannibal and devour their battered bretheren when they’re chucked in along with some potatoes."
Here is a demonstration:
As mentioned in the comments on the site linked above, there must be some new fryer oil used here. Note the ice dropped in on the video. Such strange and wonderful technology.

"...this restaurant** in Japan has a goldfish tank…in the deep fryer. Because oil floats on water, despite the massive heat (163 degrees Celsius) the goldfish simply stay away from the surface and all is well. They eat the crumbs of croquettes and other fried foods that fall to the bottom, and can live in there for 5-10 years** as they happily clean away, ignorant to the fact that certain death awaits any potential escapees.This one is hidden away back in the kitchen where customers can’t even see it, but it could easily be made for display near the dining area for everyone to see. No word on whether they turn cannibal and devour their battered bretheren when they’re chucked in along with some potatoes."
Here is a demonstration:
As mentioned in the comments on the site linked above, there must be some new fryer oil used here. Note the ice dropped in on the video. Such strange and wonderful technology.