Twaite Shad

Overview

The Twaite shad is a migratory, schooling fish belonging to the herring family. It is an anadromous species, spending most of its life in coastal marine waters before migrating into estuaries and rivers to spawn.

Distribution & habitat

This species is found throughout the Northeast Atlantic, ranging from Iceland to northern Morocco, and is also present in the North Sea, Baltic Sea, Mediterranean Sea, and Black Sea. Adults typically inhabit open coastal waters, while juveniles are often found in estuaries and near-shore environments for up to two years.

Appearance

The Twaite shad has a compressed, deep body with a distinct notch in the upper jaw and radiating ridges on its gill covers. Its back is a deep blue, transitioning to silvery-white sides. A key identifying feature is a series of 4–8 black blotches along the flanks behind the gill opening, though these can sometimes be faint or absent. It is generally smaller than the related Allis shad, typically reaching 20–40 cm in length, though it can grow up to 60 cm.

Biology & behavior

As an anadromous fish, the Twaite shad is strongly migratory. It is a planktivorous feeder, consuming invertebrates, plankton, and small fish. The species is known for its schooling behavior and its ability to navigate tidal waters during its life cycle.

Reproduction

Spawning occurs in freshwater, typically in late spring (April to June) when water temperatures reach 10–14 °C. Adults congregate near river mouths before ascending to spawn over clean gravel substrates. Unlike some other shad species, Twaite shad are iteroparous, meaning they can survive spawning and return to the sea to reproduce in multiple seasons.