NAGOYA, JAPAN - Animals in captivity have been known to form close bonds with their keepers, but have you heard of a fish that asks to be petted?
A grouper in an aquarium in Nagoya, the capital city of Japan's Aichi Prefecture, has grown so close to its keeper that it bobs to the surface to be touched and have its teeth brushed.
The 1m-long fish, housed at the Port of Nagoya Public Aquarium, often swims up to greet its keeper, 35-year-old Hitoshi Okamoto, The Japan Times said in a report on Wednesday (Dec 21).
In a video posted to YouTube by ANN News on Dec 9, the grouper is shown lifting its mouth out of the water to have its mouth petted and teeth brushed by its keeper.
Their encounters began sometime in 2014, after the fish was transferred to Nagoya from an aquarium in Mie Prefecture, The Japan Times reported.
Mr Okamoto noticed the grouper enjoyed being petted when one day, in order to coax it to eat, he poked its gums when it opened its mouth .
This progressed to tooth-brushing, which began this year.
"I've never seen a fish that has got used to humans this much," Mr Okamoto told The Japan Times.
Author and animal ethologist Jonathan Balcombe told media site thedodo.com in a 2014 article that some fish enjoy being touched by humans.
"It is a basic characteristic of animal behaviour that animals will approach desirable things and retreat from undesirable ones," he said, noting that touch is "a powerful de-stressor for animals".
Groupers are not the only fish that enjoy being petted, it seems. According to videos on YouTube, other species of fish that appear to like the interaction include koi, cichlid and discus fish.