Donald Trump upended a box of fish food into a pond of koi carp during a ritual designed to welcome visiting guests at the Akasaka Palace in Tokyo.
The US President joined Japanese prime minister Shinzo Abe in feeding the valuable fish by spooning food from a box during the ceremony.
Mr Abe finished by flicking the remaining food in his box into the pond, whereupon Mr Trump upended his with a grin.
Fish lovers gagged at the sight and wondered had Mr Trump left the koi carp — which cannot eat a large volume of food — sick or even killed them.
Twitter users said the US President had gone a step too far when he was seemingly only trying to follow Mr Abe's lead.
Lindsay Beyerstein wrote: “Trump murders beloved koi by overfeeding. It's not a Las Vegas buffet, you moron. They suffocate on the extra food!”
Sandra K Eckersley wrote: “Idiot #Trump dumps entire box of fish food in delicate Koi fish pond.”
SV Taylor posted: “Oh Dear God! Everything Trump touches dies” Gonna be a slaughter of Koi fish!”
But Ruben Rosario focused on how Mr Trump had potentially damaged this symbolic act with Mr Abe.
He posted: “Do I have to explain how F**ked up what TRUMP did to the KOI Fish IS? The KOI Fish Ceremony dates back to the days of Buddha an is Considered a source of Good Luck. To rush this is Highly Disrespectful.”
A website for fish experts and lovers - Aquascape - gives advice warning owners of koi carp not to give them too much food.
It read: “Overfeeding occurs anytime the fish are eating more than they need. This can make your fish sick.”
Mr Trump jetted into Japan during his 13-day diplomatic trek through Asia. He will next head to Korea, Vietnam and the Philippines during his five-nation tour of the region.
