The aid is worth more than $US2.6 million.
The government said the new tugboats would help improve safety and cargo handling capabilities in a country with no natural harbour.
The aquaculture equipment will be used to improve research into Nauru's coastal fish species to ensure sustainable management.
Japan also said it will provide US$49,000 to improve waste management on the small island.
Nauru Photo: Supplied/ @ChrisTrott
