Alosa agone (Scopoli, 1786)

Freyhof, JÖrg, Yoğurtçuoğlu, Baran, Jouladeh-Roudbar, Arash & Kaya, Cüneyt, 2025, Handbook of Freshwater Fishes of West Asia, De Gruyter : 63-64

Alosa agone

Common name. Twaite shad.

Diagnosis. Distinguished from other species of Alosa entering freshwater in Black Sea and Mediterranean basins by: ○ 28–50 gill rakers, rarely up to 60 / ○ length of gill rakers equal to length of branchial filaments in individuals longer than 220 mm SL / ○ no teeth on palatine / ○ dorsal profile curved / ○ usually a series of 4–8 black blotches behind gill opening (sometimes a single blotch). Size up to 500 mm SL.

Distribution. Mediterranean basin and rarely in northern Black Sea, occasionally east to Crimea. Southern Baltic east to Nemunas in Lithuania, North Sea north to Bergen, Atlantic coasts from Scotland and Ireland to Morocco. Before dams migrated from Drin to Lake Ohrid.

Habitat. At sea, pelagic. Juveniles stay close to shore and estuaries. Migrates from sea to rivers, spawning in main rivers often only a few kilometers above brackish water limit but used to ascend Rhône for 600 km and Nemunas for 400 km before construction of dams. In West Asia only known from lowermost rivers. Spawns in large rivers. Also reported in small rivers above gravel beds.

Biology. Anadromous. Males migrate upstream at 2–3 years, females at 3–4 years. Many individuals spawn for 3–4 seasons. Adults congregate near estuaries in April and enter rivers when temperatures reach 10–12°C, mainly in May–June. Spawning begins when temperatures reach about 15°C or higher in May–June. Spawns in large, very noisy schools near surface after midnight. Eggs sink to bottom or are pelagic. Spent fish migrate back to sea. Most juveniles migrate to estuary during their first summer and move to sea at end of second year, where most remain until maturity. Individual fish are thought to return to their natal spawning grounds. Northern distribution appears to be limited by water temperature. At sea, feeds mainly on crustaceans and small fish. Adults do not feed in freshwater. Juveniles feed on planktonic crustaceans.

Conservation status. LC; very locally distributed, a victim of pollution and damming of major rivers. Most populations declined in early 20 th century but appeared to have stabilised at low levels since then.

Remarks. Up to seven subspecies of A. fallax have been recognised, several of which were treated as species until recently. Molecular studies using a variety of markers have identified two major groups of populations. One is widespread in northern Europe, the Atlantic, and the westernmost Mediterranean basin ( A. fallax ), and a second is found in the Ebro ( Spain) across the northern Mediterranean basin to the east ( A. agone ). This is the one that is also found in West Asia. The molecular differences are very small, comparable to intraspecific differences in many other species. In addition, morphological differences are vague and focus on average gill raker numbers, which overlap widely between different “species”. We treat all populations of former A. fallax as A. agone , which has priority over A. fallax , which becomes a junior synonym.

Further reading. Quignard & Douchement 1991 (biology); Kottelat 1997 (systematics); Bianco 2002 (biology).

Alosa caspia ; Caspian Sea, Iran; ~ 200 mm SL.