More than 1,000 fish have died in a tank at a popular Tokyo aquarium due to oxygen deprivation.
An investigation has been launched at Sunshine Aquarium in Tokyo’s Ikebukuro district after 1,235 fish were found dead in its biggest tank.
The fish, which accounted for 94 per cent of all creatures residing in the 40-foot wide tank, were found by a security guard earlier this week.
Only 73 fish, including zebra sharks and stingrays, survived in the Sunshine Lagoon tank, which holds around 240 tonnes of water, according to reports.
The cause of the mass fish death is thought to be oxygen deprivation, after the stoppage of a bubble-generating tank cleaner hours earlier.
There are reports that staff temporarily stopped the machine in order to increase the efficacy of medicine which they had added to the water tank to treat some sick fish.
Sunshine Aquarium is home to around 37,000 fish from 750 species displayed in dozens of tanks, with other attractions including a Jelly Fish Tunnel, sea otters and penguins.
The aquarium, which is located on the rooftop of a busy commercial complex called Sunshine City, closed for one day following the discovery but has now resumed partial operations.
However, underwater performances in the tank and guided tours of the aquarium remain suspended, according to reports.
Officials at the aquarium now have cleaned out the water in the tank and plan to reintroduce new fish to the tank gradually in order to repopulate it.
Two years ago, another aquarium in the capital Tokyo Sea Life Park hit the headlines following the mysterious deaths of dozens of fish at Tokyo Sea Life leaving just one tuna roaming a once-full tank.