''Alosa'' is a genus of

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

, the river herrings, in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Alosidae The Alosidae, or the shads, are a family of clupeiform fishes. The family currently comprises four genera worldwide, and about 32 species. The shads are pelagic (open water) schooling fish, of which many are anadromous or even landlocked. Seve ...

. Along with other genera in the subfamily Alosinae, they are generally known as

shad The Alosidae, or the shads, are a family (biology), family of clupeiform fishes. The family currently comprises four genera worldwide, and about 32 species. The shads are Pelagic fish, pelagic (open water) schooling fish, of which many are anadr ...

s. 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 borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

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 east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

. Also, several taxa occur in the brackish-water

Caspian Sea The Caspian Sea is the world's largest inland body of water, described as the List of lakes by area, world's largest lake and usually referred to as a full-fledged sea. An endorheic basin, it lies between Europe and Asia: east of the Caucasus, ...

and the

Black Sea The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea 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 bound ...

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

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

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

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 ''A. pontica'' and '' A. fallax'' weighing up to 2 kg, and '' A. alosa'' can exceed 3–4 kg.

Biology

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

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

(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 The blueback herring, blueback shad, or summer shad (''Alosa aestivalis'') is an anadromous species of herring from the east coast of North America, with a range from Nova Scotia to Florida. Blueback herring form schools and are believed to mi ...

, and was later verified in laboratory studies of hearing in American shad. This ability is thought to help them avoid

dolphins A dolphin is an aquatic mammal in the cetacean clade Odontoceti (toothed whale). Dolphins belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontopori ...

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. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

. They are mostly

anadromous 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 ...

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 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, habitat refers to the array of resources, 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 manifestation of its ...

s, and many

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

are migratory. A few forms are landlocked, including one from

Killarney Killarney ( ; , meaning 'church of sloes') is a town in County Kerry, southwestern Republic of Ireland, Ireland. The town is on the northeastern shore of Lough Leane, part of Killarney National Park, and is home to St Mary's Cathedral, Killar ...

Ireland Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...

, two from lakes in northern Italy, and two in

Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...

. 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 Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

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 may be a factor in shad

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

.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. T ...

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

subgenus In biology, a subgenus ( 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 the ge ...

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

forms is rejected due to

paraphyly Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

Species by geographical origin

North America

* '' Alosa aestivalis'' ( Mitchill, 1814) (blueback herring) * '' Alosa alabamae'' D. S. Jordan and Evermann, 1896 (Alabama shad) * '' Alosa chrysochloris'' (

Rafinesque Constantine Samuel Rafinesque-Schmaltz (; 22 October 178318 September 1840) was a French early 19th-century polymath born near Constantinople in the Ottoman Empire and self-educated in France. He traveled as a young man in the United States, ult ...

, 1820) (skipjack shad) * '' Alosa mediocris'' (Mitchill, 1814) (hickory shad) * '' Alosa pseudoharengus'' ( A. Wilson, 1811) (alewife) * '' Alosa sapidissima'' (A. Wilson, 1811) (American shad)

Western Europe and the Mediterranean

* '' Alosa agone'' ( Scopoli, 1786) (agone) * '' Alosa algeriensis'' Regan, 1916 (North African shad) * '' Alosa alosa'' (

Linnaeus Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

, 1758) (allis shad) Alosa alosa

* ''

Alosa fallax The twait shad or twaite shad (''Alosa fallax'') is a species of fish in the family Alosidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea and is an anadromous fish which lives in the sea but migrates into fresh water to s ...

'' ( 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 The Pontic shad (''Alosa immaculata'', previously ''Alosa pontica''), also referred to as the Black Sea shad or Kerch shad, is a species of clupeid fish in the genus ''Alosa'', native to the Black Sea and Sea of Azov basins.E. T. Bennett, 1835 (Pontic shad) * '' Alosa kessleri'' (

Grimm Grimm may refer to: People * Grimm (surname) * Brothers Grimm, German linguists ** Jacob Grimm (1785–1863), German philologist, jurist and mythologist ** Wilhelm Grimm (1786–1859), German author, the younger of the Brothers Grimm * Christia ...

, 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 ''Alosa tanaica'', known as the Azov shad or Black Sea shad, is a species of alosid fish endemic to the Ponto-Caspian basin. It is an anadromous species, spawning in the lower reaches of rivers. It is widespread in the eastern Black Sea, the ...

'' (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 stocks, fish stock), resu ...

. 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 U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

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 W ...

, for

shad planking The Shad Planking is an annual political event in Virginia which takes place every April near Wakefield in Sussex County. It is sponsored by a chapter of the Ruritans, a community service organization which was founded in the small town of Holla ...

. American shad served as the focal point of

John McPhee John Angus McPhee (born March 8, 1931) is an American author. 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 fourt ...

's book ''The Founding Fish''.

Culinary use

The

roe Roe, ( ) or hard roe, is the fully ripe internal egg masses in the ovaries, or the released external egg masses, of fish and certain marine animals such as shrimp, scallop, sea urchins and squid. As a seafood, roe is used both as a cooking, c ...

, 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.