{{Short description|Species of fish}} {{Speciesbox | name = Twait shad | image = Alosa_fallax.jpg | status = LC | status_system = IUCN3.1 | status_ref = <ref name="iucn">{{cite iucn |author=Ford, M. |year=2024 |title=''Alosa fallax'' |volume=2024 |article-number=e.T904A58292706 |doi= |access-date=7 December 2024}}</ref> | genus = Alosa | species = fallax | authority = Lacépède, 1800 }}
The '''twait shad''' or '''twaite shad''' ('''''Alosa fallax''''') is a species of fish in the family Alosidae.<ref name="iucn"/> 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 spawn. In appearance it resembles an Atlantic herring but has a row of six to ten distinctive spots on its silvery flanks. They become mature when three or more years old and migrate to estuaries, later swimming up rivers to spawn. Populations of this fish have declined due to overfishing, pollution and habitat destruction. Conservation of this species is covered by Appendix III of the Bern Convention and Appendix II and V of the European Community Habitats Directive.
==Description== The twait shad is a typical herring-type fish and much resembles the allis shad. It has no lateral line and the belly is more rounded than that of the sprat and Baltic herring. The gill cover is ridged and the caudal peduncle has large, plate-like scales. This fish is more colourful than the Baltic herring. The back is a bluish green colour and the head brownish with a golden tinge on the operculum. The flanks are silvery, sometimes with a bronzy tinge, and there are a distinctive row of six to ten large dark spot just behind the gill cover though these may fade when the fish is dead. The adult length is typically {{convert|25|to|40|cm|0|abbr=on}}.<ref>{{cite web |url=http://www.luontoportti.com/suomi/en/kalat/allis-shad |title=Allis shad: ''Alosa alosa'' |publisher=NatureGate |access-date=14 December 2013}}</ref>
==Distribution== The twait shad is found in most of Europe and throughout the Mediterranean Sea.<ref name="iucn"/>
==Biology and lifecycle== ''Alosa fallax'' has a similar lifecycle to ''A. alosa'' (allis shad). They are known to live in sympatry.<ref name="Lochet">{{cite journal|author=Lochet, A.|author2= S. Boutry |author3= E. Rochard |title=Estuarine Phase during Seaward Migration for Allis Shad ''Alosa Alosa'' and Twaite Shad ''Alosa Fallax'' Future Spawners|journal=Ecology of Freshwater Fish |volume=18 |year=2009|issue= 2 |pages=323–335|doi= 10.1111/j.1600-0633.2008.00350.x |bibcode= 2009EcoFF..18..323L }}</ref> Some studies have suggested ''A. fallax'' and ''A. alosa'' species can hybridize.<ref name=Coscia/> They are anadromous species, like many other species in the genus ''Alosa''.<ref name="Coscia">{{cite journal|author=Coscia, I. |author2= V. Rountree|author3= J. J. King|author4= W. K. Roche|author5= S. Mariani|title=A Highly Permeable Species Boundary between Two Anadromous Fishes|journal=Journal of Fish Biology|doi=10.1111/j.1095-8649.2010.02768.x|volume=77|issue=5 |year=2010|pages=1137–1149|pmid= 21039495|bibcode= 2010JFBio..77.1137C}}</ref> However, some record of them being landlocked suggests an ability to adapt well to their environment.<ref name=Coscia/> They primarily live at sea on feeding grounds and migrate to their spawning grounds between April and June once they are sexually mature.<ref name=Coscia/> Maturity usually ranges from 3–7 years of age.<ref name=Coscia/> Juveniles appear in estuaries and brackish water around June to July.<ref name=Lochet/> The salinity of brackish water may pose problems to the juveniles migrating from fresh water.<ref name=Lochet/>
==Population reduction== Populations have been reduced primarily through overfishing, pollution, habitat destruction and migratory route obstruction in the Victorian Era.<ref>{{cite web |url=http://jncc.defra.gov.uk/protectedsites/sacselection/species.asp?FeatureIntCode=s1103 |title=1103 Twaite shad Alosa fallax - SAC selection species account |website=jncc.defra.gov.uk |archive-url=https://web.archive.org/web/20110704182249/http://jncc.defra.gov.uk/ProtectedSites/SACselection/species.asp?FeatureIntCode=S1103 |archive-date=2011-07-04}} </ref><ref name=Coscia/> Hybridization between species is more likely with species affected by human disturbances.<ref name=Coscia/> It is estimated that the estuarine phase, or the time that they are in the estuaries migrating from spawning grounds to sea, has a duration in ''A. fallax'' of up to a year and a half.<ref name=Lochet/> The estimate, however, does not take into account individual variation and survival of juveniles in the estuarine phase.<ref name=Lochet/>
==Conservation== Four special areas of conservation have been designated in Ireland where ''Alosa'' species have been known to spawn.<ref name=Coscia/> ''Alosa fallax'' has been placed in Appendix III of the Bern Convention (1979) that lists protected fauna species as well as in appendix II and V of the European Community Habitats Directive (1992) that list, respectively, species whose conservation requires the designation of special areas of conservation and that are subject to management measures."<ref name=Lochet/>
In England the Unlocking The Severn project, a consortium of the Canal & River Trust, Severn Rivers Trust, Environment Agency and Natural England is creating fish passes around weirs on the River Severn. The aim is to open {{convert|150|mi|km}} of the river for the fish to increase its freshwater breeding habitat. By 2021 passes at Diglis and Bevere, near Worcester, had been completed,<ref>{{Cite news|date=6 May 2021|title=Rare fish set for return to River Severn breeding grounds|language=en-GB|work=BBC News|url=https://www.bbc.com/news/science-environment-57016998|access-date=6 May 2021}}</ref> and by 2022 all four passes were completed and it was confirmed that the twaite shad had passed all of the passes, allowing the species to return to its natural spawning habitat.<ref>{{Cite web |date=2022-07-15 |title=Endangered twaite shad fish return to habitat unlocked after 180 years! - Unlocking the SevernUnlocking the Severn |url=https://www.unlockingthesevern.co.uk/endangered-fish-return-to-habitat-unlocked-after-180-years/ |access-date=2023-06-15 |language=en-GB}}</ref><ref>{{Cite web |title=Unlocking the Severn {{!}} Canal & River Trust |url=https://canalrivertrust.org.uk/enjoy-the-waterways/canal-and-river-network/river-severn-navigation/unlocking-the-severn |access-date=2023-06-15 |website=canalrivertrust.org.uk |language=en}}</ref>
== See also == * Shad fishing
==References== {{Reflist}}
==External links== *{{FishBase|Alosa|fallax}}
{{Taxonbar|from=Q217759}}
twait shad twait shad Category:Fish of the Black Sea Category:Fish of the Mediterranean Sea Category:Marine fish of North Africa Category:Marine fish of Europe Category:Taxa named by Bernard Germain de Lacépède Category:Taxonomy articles created by Polbot Category:Habitats Directive species