The Allis Shad fish has a dark back and a blackish spot on the shoulder. It has no lateral line, there are from 72 so 86 scales from gills to sail – and numerous fine gillrakers (from 60 to 120) visible on lifting the gill-covers.
The year-old fish – which has a row of dark blotches on the upper part of each side of the body – emigrates to the sea. The maximum length is 2.5 feet – maximum weight about 8 lbs.
The Twaite Shad fish is more common than the Allis Shad – with the same appearance and habits – though much smaller. Even when adult it retains a row of dark spots on the upper part of the body. There is no lateral line, the scales are smaller and firmer (58 to 66 in a row from gills to tail) – and gillrakers are short and stiff – numbering from 30 to 45; these characteristics distinguish the Twaite from the Allis Shad.
In the middle of the 19th Century, Shad fish were as valuable as salmon and in the estuary of the River Severn, Shad fish made up about one-third of all catches.
