It was perhaps only a matter of time before Donald Trump’s brasher instincts smashed through the ring of decorum that had held fast on his gaffe-free first day in Japan.

The victims: the colourful, and much loved, koi carp of Akasaka palace in Tokyo.

After a breakfast meeting on Tuesday – the second day of his five-nation tour of Asia – Trump chastised his hosts for unfair trade practices before an audience of Japanese and US business leaders.

Then came a meeting with the imperial couple, with all the potential for a slip-up that holds. Trump nodded and smiled as he shook hands with Emperor Akihito and Empress Michiko, but avoided the deep bow that landed Barack Obama in hot water during his first trip to Japan as president in 2009.

As it turned out, the only person who could have felt slighted was Melania Trump, who was still getting out of their armoured car – The Beast – while her husband made small talk with his hosts at the entrance to the imperial palace.

It was not the first time Trump has left the first lady behind, and may explain why she did not break into a smile until the party moved to a reception room for a chat that, as protocol dictates, was out of earshot of reporters.

But the misstep of the trip so far came in the unlikely setting of a pond in the palace grounds, home to a large collection of koi carp that have been viewed by a succession of world leaders, including Margaret Thatcher.

Presumably, the former British prime minister was less aggressive than Trump when it came to feeding the pond’s inhabitants.

Having apparently lost patience with tempting the fish to the edge with modest offerings of food, Trump simply upended his wooden container and dumped its entire contents into the water.

White House reporters captured the moment on their smartphones and tweeted evidence of the president’s questionable grasp of fish keeping.

Abe is seen grinning, as is a woman in a kimono standing to one side. Next to her, Rex Tillerson – perhaps grateful for a moment of comic relief after he was named in the Paradise Papers – could not suppress a laugh, according to witnesses.

Some speculated that a poor palace employee would be dispatched to the scene of Trump’s faux pas to the clean up the mess as soon as the two leaders disappeared inside.

Trump is not alone in misjudging the fishes’ appetite, however. According to the Aquascape website, overfeeding is the most common mistake made by keepers of koi carp.

“This can make your fish sick, and excessive amounts of waste that strains the limits of what can be biologically reduced, results in a decline of water quality,” the site says.