The world must stop treating the oceans as a "waste swimming pool" for pollution, a senior U.N. official said on Friday at the debut in Oslo of a $65 million research ship to help developing nations manage fish stocks. The 75-metre long Dr Fritjof Nansen, funded by Norway, will help understand fish stocks mainly off Africa to avert over-fishing and pollution that have depleted many commercial fish stocks worldwide. The vessel will start its first mapping mission off West Africa in May, in a joint U.N. and Norwegian program.