Unholy mackerel! Fish waste fumes blamed for knocking out boat crew.

Toxic fumes from fish waste may have knocked out an entire crew of a fishing boat in the sweltering heat on Tuesday, according to safety officials.

A fishing boat is docked at Dongho Port in Tongyeong, South Gyeongsang, on July 8. [YONHAP]

Toxic fumes from fish waste may have knocked out an entire crew of a fishing boat in the sweltering heat on Tuesday, according to safety officials.

A total of four crew members were found unconscious from apparent suffocation Tuesday morning aboard a mackerel fishing vessel docked at Dongho Port in Tongyeong, South Gyeongsang. None of the workers' lives are in danger, according to the Coast Guard.

The 9.7-ton ship was moored at the port when, at around 8:32 a.m., the crew members collapsed inside the ship's fish hold. The four included the ship's chief engineer, a Korean man in his 60s, and three foreign crew members in their 20s and 30s from Indonesia and East Timor.

Authorities believe the suffocation occurred due to toxic gases accumulating inside the hold. Emergency responders arrived at the scene and transported the four individuals — who were breathing but in varying states of consciousness — to a hospital. All four later regained full consciousness following treatment.

The incident occurred when the chief engineer and one of the foreign sailors entered the hold to clean it, and they subsequently collapsed, according to authorities. Two more crew members who attempted to rescue them also lost consciousness.

The fish hold had been emptied a few days earlier after the latest catch was unloaded, according to the Coast Guard. Investigators suspect the recent hot weather may have caused residual seafood waste to emit hazardous gases.

An investigation is ongoing to determine the exact cause of the incident.

BY KIM MIN-YOUNG [kim.minyoung5@joongang.co.kr]