The sight of several sailfish being hung out to defrost in front of the Great Atlantis Seafood Centre in Marina Country Club in Punggol on Sunday has irked some Singaporean anglers.
The anglers say the fish should be released after they are caught.
Photographs of the sailfish at the restaurant were posted on citizen-journalism website Stomp on Monday.
Sailfish are so named for their dorsal fin, known as a sail, which often spans the entire length of the back.
The manager of Great Atlantis Seafood Centre, Mr Victor Yi, said: "The fish were not caught by us but by Malaysian fishermen in Malaysian waters."
He added that the restaurant bought six or seven sailfish for $10 per kilogram from the fishermen. The restaurant plans to use the fish to prepare fish and chips. Mr Yi said he believes the fish have already been cut into fillets.
The World Wide Fund for Nature (WWF) lists sailfish as a "priority species", along with marlin, swordfish and spearfish.
Ms V. Prema, director of communications at WWF Singapore, said sailfish are "at risk from overfishing and as a target in recreational fishing".
She added that WWF Singapore discourages people from buying sailfish if they are caught in the wild in a way that depletes their numbers.
However, an Agri-Food and Veterinary Authority of Singapore spokesman said that sailfish are "not protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites), and are allowed to be imported".
Cites is an international agreement drawn up in 1973 to protect wildlife. Singapore has been a signatory of the convention since 1986.
Angler R. Teo, 36, said one of the practices among anglers is to release fish which are fished for recreation, such as sailfish.
Another angler, Mr William Ow, 32, was not angered over the sailfish incident. He said other anglers might have been angry because catching the fish for food would deplete the supply available for recreational fishing.
"Nobody eats sailfish, as it does not taste as good as other fish. Anglers who catch it usually release it," he said.
Some netizens did not have any issue with the sailfish incident. Said netizen loverangel10: "It's just fish."