Banksy has confirmed he is behind a new swimming fish artwork which has appeared on a police sentry box in the City of London.

It marks the seventh animal-themed piece the elusive street artist has claimed this week by posting a photo of the artworks to his Instagram at 1pm.

The artist appears to have used translucent spray paint on the glass windows to create the design, turning the sentry box into what looks like a giant fish tank.

The piece differs from Banksy’s previous dark silhouette images of a goat, elephants, monkeys, a wolf, pelicans and a cat which have popped up in various locations across London since Monday.

The governing body of the City of London has said it is working on options to “preserve” the new artwork after the artist confirmed it was his by posting an uncaptioned image on Instagram which sees a police officer taking a photo of the piece.

A City of London Corporation spokesperson said in a statement to the PA news agency: “We’re aware of the works on the City of London police box on Ludgate Hill.

“We are currently working through options to preserve the artwork.”

A man with a City of London high-vis vest was spotted taking pictures of the artwork on Sunday afternoon.

After it appeared, two City of London police officers turned up to examine the piece and the force said it was liaising with the City of London Corporation on what was to be done with the artwork.

In a statement to PA, Detective Chief Inspector Andy Spooner, for the City of London Police, said: “We are aware of criminal damage to a City of London Police box in Ludgate Hill. We are liaising with the City of London Corporation who own the police box.”

After Banksy confirmed it was his, a small crowd gathered to see the piece while a City of London Police officer is keeping watch of the police box.

Photographer Avi Yasitli, 63, who has been to see all of the Banksy pieces of art this week except one piece which was taken, said he thinks the animals are a message from the artist that the city has “turned into a zoo”.

Artist Daniel Lloyd-Morgan, who has painted most of Banksy’s pieces of art this week, said the new collection is “really uplifting for people in London at the moment”.

“There’s a buzz around his work. It’s nice to capture that as I do the people as well”, he added.

“It’s not just about the artwork, it’s about the whole environment he’s creating, it becomes a sort of work of art itself – what happens to it, people steal it or take it away.”

A local resident was also amongst those to come visit the piece as she wanted to see it in case anything happened to it later in the day.

The woman, who did not want to be named, said: “I walked up here yesterday and I don’t remember seeing it, I think I would have noticed it.

“I like it, it’s got a charm to it somehow. It’s not in your face, it’s quite subtle.”

On Saturday, the artist’s sixth piece – a stretching cat on an empty, distressed advertising billboard – was removed from its location in north-west London hours after it was revealed.

Crowds booed as the piece in Cricklewood was dismantled by three men who said they were “hired” by a “contracting company” to take down the billboard for safety reasons.

A contractor, who only wanted to give his name as Marc, told PA they were going to take the board down on Monday and replace it, but the removal had been brought forward to Saturday in case someone “rips it down and leaves it unsafe”.

An officer at the scene told PA that the owner of the billboard has told police he will donate it to an art gallery.

The cat design was the second piece to be removed during the week after a painting of a howling wolf on a satellite dish was taken off the roof of a shop in Peckham, south London, less than an hour after it was unveiled.

It was removed by three men, according to a witness, who told PA that he filmed them, which led to one of the men throwing his phone on a roof.

A spokesman for Banksy told PA that the artist is neither connected to nor endorses the theft of the wolf design and that they have “no knowledge as to the dish’s current whereabouts”.

The first piece of graffiti in Banksy’s new animal-themed series, which was announced on Monday, is near Kew Bridge in south-west London and shows a goat with rocks falling down below it, just above where a CCTV camera is pointed.

On Tuesday, the artist added silhouettes of two elephants with their trunks stretched towards each other on the side of a building in the Chelsea area of west London.

This was followed by three monkeys looking as though they were swinging underneath a bridge over Brick Lane, near a vintage clothing shop in the popular east London market street, not far from Shoreditch High Street.

The fifth design, of pelicans pinching fish from a London chip shop sign in Walthamstow, east London, was revealed on Friday.