Olive flounder

The olive flounder (Paralichthys olivaceus), bastard halibut, Japanese flounder or Korean halibut is a temperate marine species of large-tooth flounder native to the North-western Pacific Ocean. It is the highest valued finfish in the world, known to be excellent for aquaculture due to a rapid growth rate and popularity in Japan and Korea.^[1]

Olive flounder
In a supermarket display tank
Drawing by Kawahara Keiga
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Carangiformes
Suborder:	Pleuronectoidei
Family:	Paralichthyidae
Genus:	Paralichthys
Species:	P. olivaceus
Binomial name
Paralichthys olivaceus (Temminck & Schlegel, 1846)
Synonyms
Hippoglossus olivaceus Temminck & Schlegel, 1846

Names

In Japanese, olive flounder is called hirame (ヒラメ). In Korean, it is called gwangeo (광어; 廣魚; lit. flatfish). In Chinese, it is called yaping (牙鮃) or biankouyu (扁口魚).

In English, it is often referred to as "Japanese flounder" or "Korean flatfish" when mentioned in the context of those countries.

Description

It reaches a length of 103 cm (41 in) and a weight of 9.1 kg (20 lb).^[2] In 2017 its genome and transcriptome was sequenced as a model to study flatfish asymmetry.^[3]

• 
  Specimen at Joetsu Aquarium
• 
  Closeup of eyes

Habitat and diet

The olive flounder is often found in soft and muddy offshore, coastal areas where the water level goes down to 100 m in depth. The temperature of water in these areas range from 21–24 °C or 69–75 °F.^[1] Some flounder have been found in the Mariana Trench.^{[citation needed]}

Olive flounder typically eat fish spawn, crustaceans, polychaetes, and small fish.^{[citation needed]}

Life cycle

Olive flounder spawn anytime from January through August in shallow water, roughly about 70 cm in depth. The egg and larvae remain that way for about 24–50 days after hatching. Once they begin their metamorphosis process, they move towards more sandy areas and feed on shrimp. After achieving metamorphosis, the flounder move offshore and begin feeding on bigger fish in order to grow to their adult size.^[1]

How they become "flatfish"

Olive flounder first start out upright like normal fish, but then after 24 to 50 days after hatching they turn onto their side. Their previous side now becomes their belly or their underside and then their eye and nostril move towards what is now considered the back. This process is typically called the "metamorphosis."^[1]

Aquaculture

Capture (blue) and aquaculture (green) production of Bastard halibut (Paralichthys olivaceus) in thousand tonnes from 1950 to 2022, as reported by the FAO^[4]

The olive flounder is the most common flatfish species raised in aquaculture in Korea. They are raised in Japan and China as well. It is the most highly prized of the Japanese flounders. Although the aquaculture for the olive flounder started from the late 1980s, its commercial production didn't begin on a major scale until the 1990s in Korea.

Parasites and food poisoning

Kudoa septempunctata in olive flounder muscles

The myxozoan Kudoa septemlineata has been described in 2010 from olive flounder from Korea.^[5] This microscopic parasite infects the trunk muscles of the olive flounder where it causes myoliquefaction. Ingestion of raw fish containing K. septemlineata spores has been reported as a cause of food poisoning (gastroenteritis) in Japan since 2003.^[6][7] However, laboratory studies performed in 2015 and 2016 on adult^[8] and suckling mice^[9] showed that K. septemlineata spores were excreted in faeces and did not affect the gastrointestinal tract.

As food

Oliver flounder is widely eaten as food in East Asia, often raw.

• 
  Korean hoe
• 
  Japanese sushi
• 
  Italian carpaccio
• 
• 

Appearances in media

The olive flounder has appeared in the video game series Animal Crossing as one of the various fish species the player is able to catch using a fishing rod.^[10]