Blue-backed fish;
also referred to as
Blue-fish (青魚 aozakana)
is a category of fish used in Japanese cuisine

Japanese cuisine

Japanese cuisine has developed over the centuries as a result of many political and social changes throughout Japan. The cuisine eventually changed with the advent of the Medieval age which ushered in a shedding of elitism with the age of shogun rule...

 that have a rich and fatty taste, and are distinguished from another category of white meat fish that tend to have a lighter and more delicate flavor. It is not a scientific categorization, but refers to commonness in outer appearance, fleshiness and oiliness and include such species of fish as sardine

Sardine

Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....

, mackerel

Mackerel

Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...

, herring

Herring

Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

, perch

Perch (disambiguation)

Perch may refer to:*Perch , a surname *The USS Perch, multiple ships with the name*Perch , antique unit of measure of length, area or volume, depending on context, used in medieval France and the British Isles...

 and anchovy

Anchovy

Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...

. Blue-backed fish tend to be high in the essential amino acid, histidine

Histidine

Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...

, as well as the omega-3 fatty acid

Omega-3 fatty acid

N−3 fatty acids are essential unsaturated fatty acids with a double bond starting after the third carbon atom from the end of the carbon chain....

s, eicosapentaenoic acid

Eicosapentaenoic acid

Eicosapentaenoic acid is an omega-3 fatty acid. In physiological literature, it is given the name 20:5. It also has the trivial name timnodonic acid...

(EPA) and docosahexaenoic acid

Docosahexaenoic acid

Docosahexaenoic acid is an omega-3 fatty acid that is a primary structural component of the human brain and retina. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain and six cis double bonds; the first double bond is located at the third carbon from the omega end...

(DHA), and are generally said to have health benefits when included in a balanced diet, including such effects as reducing cholesterol.

Almost without exception, blue-backed fish are salt water fish that travel in schools close to the surface of the water, have wide migratory patterns and are relatively low on the food chain so feed on plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

, etc. Their appearance, as is indicated by their name, is a dark blue dorsal with a nearly white under belly. Further, blue-fish are generally fairly small in size and caught in large quantities resulting in low market price, so are thought of as mass-market fish for general consumption and are distinguished from larger, specialty fish caught in smaller quantities, even if they share other qualities.

Examples

Blue-backed fish include:

• Clupeiformes
  Clupeiformes
  Clupeiformes is the order of ray-finned fish that includes the herring family, Clupeidae, and the anchovy family, Engraulidae. The group includes many of the most important food fish....
  
  : the order of ray-finned fish that includes Clupeidae (the herring family) and Engraulidae (the anchovy family)
• Beloniformes
  Beloniformes
  The Beloniformes are an order of five families of freshwater and marine ray-finned fish: the Adrianichthyidae ; Belonidae ; Exocoetidae ; Hemiramphidae ; and the Scomberesocidae...
  
  : the order of ray-finned fish that includes Adrianichthyidae (ricefish and medakas); Belonidae (needlefish); Exocoetidae (flyingfishes); Hemiramphidae (halfbeaks): and the Scomberesocidae (sauries).
• Perciformes
  Perciformes
  The Perciformes, also called the Percomorphi or Acanthopteri, is one of the largest orders of vertebrates, containing about 40% of all bony fish. Perciformes means perch-like. They belong to the class of ray-finned fish and comprise over 7,000 species found in almost all aquatic environments...
  
  : the perch-like order of ray-finned fish comprising over 7000 different species.