The body of a fisherman was brought ashore in a frozen state from a boat in Samut Prakan province on Friday.
His friends said he had hanged himself on another boat, according to a Thairath Oline report.
When police reached the Saphan Pla port, they found the frozen body of a man wrapped in a canvas sheet in the cold storage underneath the fishing boat.
The dead man was identified as Charan Eksupaphan, 51, with a Saraburi province home address.
Apart from bruises around his neck, he had no other injuries.
Prasart Sriaram, 47, the captain of the boat, said Charan had worked for the fishing company for several years before resigning. He rejoined the company in mid-January as the crew supervisor of the Hor Charoen Samut 12, which is fishing near Malaysian waters.
At around 8.30pm on Thursday, Mr Prasart was contacted by the Hor Charoen Samut 12 and told that a man had hanged himself in his cabin on the second deck.
He brought his boat to pick up the body since the Hor Charoen Samut 12 would have to stay in the southern waters for another two months before returning.
None of crew members were aware is Charan had any problems.