Djiba Kamara said he was picked up by the Ghanaian navy patrol at 2am
Police in Ghana have impounded a Chinese ship and arrested three crew members after three Ivorians are alleged to have been thrown overboard.
One of the stowaways is believed to have drowned; the other two survived.
Djiba Kamara, 18, was rescued by a navy patrol on Sunday after he said he had been treading water for seven hours.
Stowaways are protected under the UN's Universal Declaration of Human Rights and are the responsibility of a ship's crew if found.
The BBC's David Amanor in Ghana's capital, Accra, says they are also entitled to be fed.
Evidence
Mr Kamara told Ghana's state-owned Daily Graphic paper the three stowaways were thrown into the sea on Saturday night after being discovered in the crane of the MV Rui Ning 3.
One of his companions, Omari Ceesay, 33, was found unconscious but survived and is said to be in a stable condition at a naval hospital in the Ghanaian port city of Takoradi.
Mr Kamara said the third man, Kondah Aziz, could not swim.
Amidu Mahama, Ghana's Western Region police commander, told the BBC that evidence had been found on board that appeared to corroborate the Ivorian survivor's story.
He said the police are waiting for advice from Ghana's attorney-general and ministry of foreign affairs on how to proceed.
Our correspondent says reliable information suggests the stowaways slipped aboard the Chinese ship while docked in the Ivorian port of Abidjan.
The merchant ship proceeded to Takoradi to load a cargo of bauxite believed to be destined for China; although the stowaways may have thought it was bound for the United States, he says.
According to the Universal Declaration of Human Rights, the captain and crew may be fined or jailed if the human rights of a stowaway are violated.