This fish becomes mature when three or more years old and migrates to estuaries, later swimming up rivers to spawn.

The back is a bluish-green colour and the head brownish with a golden tinge on the operculum.

[5] The estuarine phase, or the time spent in estuaries migrating from spawning grounds to sea, is estimated to have a duration in A. alosa of up to six months.

[5] The estimate, however, does not take into account individual variation and/or survival of juveniles in the estuarine phase.

[1] The International Union for Conservation of Nature listed the species as critically endangered in 2024, citing an estimated global population decline of around 80% over the past 20 years, leaving many small relict subpopulations and extirpating others.

[1] Four special areas of conservation have been designated in Ireland where Alosa species have been known to spawn.

[6] Alosa alosa "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.