''Alosa'' is a genus of

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

, the river herrings, in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Clupeidae Clupeidae is a family of ray-finned fishes, comprising, for instance, the herrings, shads, sardines, hilsa, and menhadens. The clupeoids include many of the most important food fishes in the world, and are also commonly caught for producti ...

. Along with other genera in the subfamily

Alosinae The Alosinae, or the shads,Alosinae

, they are generally known as

shad The Alosinae, or the shads,Alosinae
tp://ftp.fao.org/docrep/fao/009/ac482e/ac482e27.pdf Subfamily AlosinaeFAO Fisheries Bulletin They are distinct from other herrings by having a deeper body and spawning in rivers. Several species can be found on both sides of the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

and the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...

. Also, several taxa occur in the brackish-water

Caspian Sea The Caspian Sea is the world's largest inland body of water, often described as the world's largest lake or a full-fledged sea. An endorheic basin, it lies between Europe and Asia; east of the Caucasus, west of the broad steppe of Central A ...

and the

Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Rom ...

basin. Many are found in fresh water during spawning and some are only found in landlocked fresh water.

Fossil record

These fishes lived from the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

to Quaternary (from 55 million years ago to now). Fossils have been found in Canada, the United States, Greece, Kazakhstan, Azerbaijan, Hungary, Romania, and Italy. Clupeidae - Alosa elongata

Appearance

''Alosa'' species are generally dark on the back and top of the head, with blue, violet, or greenish tints. Some can be identified as having a grey or green back. Spots are commonly found behind the head, and the fins may vary from species to species or individually. Most species of ''Alosa'' weigh or less, with one species, ''A. pontica'', weighing up to 2 kg.

Biology

Shads are thought to be unique among the fishes in having evolved an ability to detect

ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...

(at frequencies above 20 kHz, which is the limit of human hearing).Mann, D. A.; Higgs, D. M.; Tavolga, W. N.; Souza, M. J.; and Popper, A. N. (2001). Ultrasound detection by clupeiform fishes. ''Journal of the Acoustical Society of America'' 109:3048–3054 This was first discovered by fisheries biologists studying a type of shad known as blueback herring, and was later verified in laboratory studies of hearing in American shad. This ability is thought to help them avoid dolphins that find prey using echolocation. ''Alosa'' species are generally

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

. They are mostly anadromous or semianadromous with the exception of strictly freshwater landlocked species. ''Alosa'' species are generally migratory and schooling fish. Males usually mature about a year before females; they spawn in the late spring to summer. Most individuals die shortly after spawning. ''Alosa'' species seemingly can change readily to adapt to their environments, as species are found in a wide range of temperatures and waters.

Lifecycle and reproduction

As ''Alosa'' species are generally anadromous, they face various obstacles to survival.Lochet, A., S. Boutry, and E. Rochard. ''Estuarine Phase during Seaward Migration for Allis Shad Alosa Alosa and Twaite Shad Alosa Fallax Future Spawners.'' Ecology of Freshwater Fish 18 (2009): 323-35. They may have to pass through numerous barriers and waters to get to either their spawning grounds or normal habitats (the sea in most cases). Estuaries are a major factor in numerous ''Alosa'' species' migrations. Estuaries can be highly variable and complex environments contributing to fluctuating biological interactions, with shifts in osmolarity, food sources, predators, etc. Since many adult ''Alosa'' species die after spawning, only the young generally to migrate to the sea from the spawning grounds. Duration of migration varies among fish, but can greatly affect survival. Reproduction varies by species. Studies done on ''Alosa'' in Iranian waters have shown that spawning varies in time, place, and temperature of the waters they inhabit. Fecundity may also vary. Species are known to spawn as early as April or as late as August. Temperatures range from about 11 to 27 °C. Fecundity can range from 20,000 to 312,000 eggs. Eggs are pelagic. Geography and temperature are important environmental factors in egg and young-of-year development. The lifespan of ''Alosa'' species can be up to 10 years, but this is generally uncommon, as many die after spawning.

Systematics

The systematics and distribution of ''Alosa'' shads are complex. The genus inhabits a wide range of

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s, and many taxa are migratory. A few forms are landlocked, including one from Killarney in

Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the s ...

, two from lakes in northern Italy, and two in

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...

. Several species are native to the Black and Caspian Seas. ''Alosa'' species of the Caspian are systemically characterized by the number of rakers on the first gill arch.Malkin, E. M., and S. B. Andrianova. ''Biology and Traits of the Formation of Stock of Big-eyed Shad Alosa Saposchnikowii.'' Journal of Ichthyology 48.6 (2008): 443-51. They are classified as being "multirakered", "medium-rakered", or "oligorakered". The multirakered are primarily plankton feeders, the oligorakered have large rakers and are predators, and the medium-rakered generally consume a mixed diet. Most current species of the genus ''Alosa'' in North America can be found in Florida, whereas the distribution of most of them is broader.Richard S. McBride (2000). ''Florida's Shad and River Herrings (Alosaspecies): A Review of Population and Fishery Characteristics''. Florida MAR8INE Research Institute Technical Reports: Technical Report TR-5, Florida Fish and Wildlife Conservation Commission. St. Petersburg, Florida. Morphology is notoriously liable to adapt to changing food availability in these fish. Several taxa seem to have evolved quite recently, making molecular analyses difficult. In addition,

hybridization Hybridization (or hybridisation) may refer to: *Hybridization (biology), the process of combining different varieties of organisms to create a hybrid *Orbital hybridization, in chemistry, the mixing of atomic orbitals into new hybrid orbitals *Nu ...

may be a factor in shad

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological s ...

.Faria, R.; Weiss, S.; and Alexandrino, P. (2006). ''A molecular phylogenetic perspective on the evolutionary history of ''Alosa'' spp. (Clupeidae).'' ''Molecular Phylogenetics and Evolution'' 40(1): 298–304. (HTML abstract). Nonetheless, some trends are emerging. The North American species except the

American shad The American shad (''Alosa sapidissima'') is a species of anadromous clupeid fish naturally distributed on the North American coast of the North Atlantic, from Newfoundland to Florida, and as an introduced species on the North Pacific coast. Th ...

''A. sapidissima'' can probably be separated in a

subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between ...

''Pomolobus''. Conversely, the proposed genus (or subgenus) ''Caspialosa'' for the

forms is rejected due to paraphyly.

Species by geographical origin

North America

* '' Alosa aestivalis'' ( Mitchill, 1814) (blueback herring) Blueback herring fish (white background)

* '' Alosa alabamae'' D. S. Jordan and Evermann, 1896 (Alabama shad) * '' Alosa chrysochloris'' ( Rafinesque, 1820) (skipjack shad) Skipjack herring fish alosa chrysochloris (white background)

Skipjack herring fish alosa chrysochloris (white background)

* '' Alosa mediocris'' (Mitchill, 1814) (hickory shad) Hickory shad (Duane Raver)

* ''

Alosa pseudoharengus The alewife (''Alosa pseudoharengus'') is an anadromous species of herring found in North America. It is one of the "typical" North American shads, attributed to the subgenus ''Pomolobus'' of the genus ''Alosa''. As an adult it is a marine spe ...

'' ( A. Wilson, 1811) (alewife) Alewife fish (white background)

* '' Alosa sapidissima'' (A. Wilson, 1811) (American shad) American shad fish alosa sapidissima (white background)

Western Europe and the Mediterranean

* '' Alosa agone'' ( Scopoli, 1786) (agone) * '' Alosa algeriensis''

Regan The family name Regan, along with its cognates O'Regan, O Regan, Reagan, and O'Reagan, is an Anglicized form of the Irish surname Ó Riagáin or Ó Ríogáin, from Ua Riagáin. The meaning is likely to have originated in ancient Gaelic ''ri'' ...

, 1916 (North African shad) * ''

Alosa alosa The allis shad (''Alosa alosa'') is a widespread Northeast Atlantic species of fish in the herring family, Clupeidae. It is an anadromous fish which migrates into fresh water to spawn. It is found in the eastern Atlantic Ocean, the western Bal ...

'' ( Linnaeus, 1758) (allis shad) Alosa alosa

* '' Alosa fallax'' ( Lacépède, 1803) (twait shad) * '' Alosa killarnensis'' Regan, 1916 (Killarney shad)

Caspian Sea, Black Sea, the Balkans

* '' Alosa braschnikowi'' ( Borodin, 1904) (Caspian marine shad) * '' Alosa caspia'' ( Eichwald, 1838) ** ''A. c. caspia'' (Eichwald, 1838) (Caspian shad) ** ''A. c. knipowitschi'' (Iljin, 1927) (Enzeli shad) ** ''A. c. persica'' (Iljin, 1927) (Astrabad shad) * '' Alosa curensis'' ( Suvorov, 1907) (Kura shad) * '' Alosa immaculata'' E. T. Bennett, 1835 (Pontic shad) * '' Alosa kessleri'' ( Grimm, 1887) (Caspian anadromous shad) * '' Alosa macedonica'' ( Vinciguerra, 1921) (Macedonia shad) * '' Alosa maeotica'' (Grimm, 1901) (Black Sea shad) * '' Alosa saposchnikowii'' (Grimm, 1887) (Saposhnikovi shad) * '' Alosa sphaerocephala'' ( L. S. Berg, 1913) (Agrakhan shad) * '' Alosa tanaica'' (Grimm, 1901) (Azov shad) * '' Alosa vistonica'' Economidis and Sinis, 1986 (Thracian shad) * '' Alosa volgensis'' ( L. S. Berg, 1913) (Volga shad)

Recreational fishing

Commercial fishing

Management

Shad populations have been in decline for years due to spawning areas blocked by dams, habitat destruction, pollution, and

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...

. Management of shad has called for more conservative regulations, and policies to help the species have lower fishing mortality.

Political significance

Shad serve a peculiar symbolic role in

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth are ...

state politics. On the year of every gubernatorial election, would-be candidates, lobbyists, campaign workers, and reporters gather in the town of

Wakefield, Virginia Wakefield is an incorporated town in Sussex County, Virginia, United States. Per the 2020 census, the population was 729. Wakefield is widely known for the Virginia Diner, the Airfield Conference and 4-H Educational Center, and the National We ...

, for shad planking. American shad served as the focal point of

John McPhee John Angus McPhee (born March 8, 1931) is an American writer. He is considered one of the pioneers of creative nonfiction. He is a four-time finalist for the Pulitzer Prize in the category General Nonfiction, and he won that award on the four ...

's book ''The Founding Fish''.

Culinary use

The roe, or more properly the entire engorged uterus of the

—filled with ripening eggs, sautéed in clarified butter and garnished with parsley and a slice of lemon—is considered a great delicacy, and commands high prices when available.

References

External links

Tastes of the Region: Shad
An article celebrating shad's cultural importance to the Hudson Valley

Science Cheerleader - Shad: Our Pollution vs. Their Resolution.
{{Taxonbar, from=Q344999 Commercial fish Extant Eocene first appearances Marine fish genera Ray-finned fish genera