Eleotris Sandwicensis
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''Eleotris sandwicensis'', commonly known as the Sandwich Island sleeper, the Hawaiian sleeper, or oopu, is a species of fish in the family
Eleotridae Eleotridae is a family of fish commonly known as sleeper gobies, with about 34 genera and 180 species. Most species are found in the tropical Indo-Pacific region, but there are also species in subtropical and temperate regions, warmer parts of t ...
.
Endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
to the
Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...
, 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 Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...
. ''Eleotris sandwicensis'' is a dorso-ventrally flattened fish, almost like a smaller
catfish Catfish (or catfishes; order (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...
. 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 . It is locally important to
commercial fisheries Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often p ...
and is also used as bait by fishermen after larger fishes. In the
Hawaiian language Hawaiian (', ) is a critically endangered Polynesian language of the Austronesian language family, originating in and native to the Hawaiian Islands. It is the native language of the Hawaiian people. Hawaiian, along with English, is an offi ...
, the fish is also known as ''oau'', ''owau'', and ''hiu kole''.


Anatomy and morphology

''Eleotris sandwicensis'' is an ambush predator that uses suction to hunt its prey. Like other species that rely on suction to capture prey, ''Eleotris sandwicensis'' has enhanced cranial muscles and The distribution of ''E. sandwicensis'' is limited as this species does not have the ability to travel upstream of steep waterfalls due to their lack of pelvic fins.


Distribution

''Eleotris sandwicensis'' is an endemic species of Hawaii that inhabits estuarine regions.


Habitat

This species can be found in the lower parts of streams and in the ocean as hatchlings, proceeding into the lower part of streams soon after. Within the streams ''Eleotris sandwicensis'' is most commonly found in pools, runs, and fast riffles.


Reproduction

''Eleotris sandwicensis'' releases eggs into the streams that it inhabits. After these eggs hatch, the larvae begin to move downstream towards the ocean. In the ocean, the larvae live for the next five months until they are ready to migrate back into fresh water streams, where they will reside for the rest of their lives. During these reproductive cycles, ''Eleotris sandwicensis'' can produce anywhere between 5000 and 55000 eggs.


Diet

''Eleotris sandwicensis'' is considered an ambush predator that uses suction to hunt its prey. When hunting ''Eleotris sandwicensis'' will eat any type of fish or insects it can find.


Threats

Birds and other native fish are all predators to ''Eleotris sandwicensis''. Some examples of threats to ''Eleotris sandwicensis'' are the
black-crowned night heron The black-crowned night heron (''Nycticorax nycticorax'') r black-capped night heron commonly shortened to just night heron in Eurasia, is a medium-sized heron found throughout a large part of the world, including parts of Europe, Asia, and Nort ...
(''Nycticorax nycticorax''), āholehole (''Kuhlia marginata'') and the silvermouth trevally (''Ulua aurochs''). Other dangers that ''Eleotris sandwicensis'' can encounter include the degradation of the estuarine regions and invasive species.''’o’opu ’Akupa or Sandwich Island Sleeper''
dlnr.hawaii.gov/wildlife/files/2019/03/SWAP-2015-Eleotriss-oopu-akupa-Final.pdf.
/ref> The degradation of estuarine regions will not affect the species itself but its ability to reproduce, through the degradation of the habitat the flow of water may not function how it previously did causing delays or prevention of larvae ability to travel into the ocean and come back to the streams after their five month period at sea.  With the introduction of invasive species comes unknown diseases and parasites, as well as the invasive species itself being a direct threat to the species whether it be through attacking the species or stealing the food of the species. With all these factors the introduction of a new species can drastically affect any species due to the many variables introduced when they arrive.


Human use

This species is consumed and used for bait to catch pāpio which are younger ''
Ulua aurochs Ulua may refer to: * Ulúa River * San Juan de Ulúa, a complex located on an island of the same name in the Gulf of Mexico * USS ''Ulua'' (SS-428), a submarine of the United States Navy * ''Ulua'' (fish), a genus of fishes in the family Carangid ...
''.


References


Further reading

* * *


External links


Photograph
sandwicensis Freshwater fish of Hawaii Endemic fauna of Hawaii Fish described in 1875 Taxonomy articles created by Polbot {{Eleotridae-stub