The Housing Development Board (HDB) allows homeowners to keep certain pets, including species of fish that are not endangered.

One particular owner, however, decided to take it to the next level and built a koi fish tank on the stairs outside of his unit:

[video poster="https://static.mothership.sg/1/2018/08/koi-hdb-mp4-image.jpg" width="1280" height="720" mp4="https://static.mothership.sg/1/2018/08/koi-hdb.mp4"][/video]

For the data-poor:

HDB permit needed

The aquarium page that uploaded the video explained that it was two units combined into one, which ostensibly meant that the homeowner uses the other set of stairs to enter and leave the house.

Commenters also seemed quite sure that the unit is in Tampines.

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However, for tanks that are not on a cabinet/table or the floor, owners are required to submit an application to the relevant HDB branch for approval:

Overcrowded pond?

As the video went viral with close to 5,000 shares and almost 500 comments, some Facebook users have expressed their concern over the lack of space for the fish.

From the video, there were around 10 fish huddled in the tank:

Ideal living conditions for Koi

Besides high oxygen levels and enough shade, Kois need to be raised on ample space — in fact, multiple fish rearing sites have supplemented that the general rule for fish is 10 gallons (37.8 litres) of water to an inch of fish.

The pond should also be at least three to four feet (that's 0.9m to 1.2m) deep.

The average house koi will grow to be around 21 inches (53 cm), although it can grow up to 36 inches(91cm) if conditions allow.

Top image from Aqua Lush Facebook page