Eleotris sandwicensis, commonly known as the Sandwich Island sleeper, the Hawaiian sleeper, or oʻopu, is a species of fish in the family Eleotridae. Endemic to the Hawaiian Islands, it can be found in marine, fresh, and brackish waters around the coast. Due to this capability of migrating between different marine environments, it is considered amphidromous. Eleotris sandwicensis is a dorso-ventrally flattened fish, almost like a smaller catfish. It varies in color, but is most commonly darker black/gray or brown with green/yellow spots surrounding its body. This fish can reach a length of 33 cm (13 in). It is locally important to commercial fisheries and is also used as bait by fishermen after larger fishes. In the Hawaiian language, the fish is also known as ʻoau, ʻowau, and hiʻu kole.

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