An ilish is an edible fish, one that plays an important role in the Bengali cuisine of the Indian subcontinent, especially in Bangladesh. The formal name for the species is Tenualosa ilisha. Ilish are closely related to shad and herring, and hilsa shad, or just hilsa, are other common names for the same fish. They are anadromous fish: Ilish live as adults in the ocean but swim up rivers to lay their eggs. The young hatch in the rivers and swim downstream to reach the ocean.
Ilish have compressed bodies that are deeper than they are wide. Their sides bulge out slightly and are covered with medium-sized silver scales with gold and purple overtones. The fish have a distinctive central notch in their upper jaws. Adults average 14 to 16 inches (36 to 42 cm) in length and weigh up to 5.5 pounds (2.5 kg) Females are usually larger than males.
Their native waters are the Persian Gulf, the Bay of Bengal, and surrounding ocean areas. Migrations for spawning take the fish up many rivers, including the Tigris and Euphrates of Iran, several Indian rivers, and many major rivers in Bangladesh. Ilish are fast swimmers and have been known to travel as far as 44 miles (71 km) in a day. They migrate up to 750 miles (1,200 km) in some rivers to breed. Some longer rivers, including the Ganges, seem to have permanent populations in their higher reaches.
The major spawning runs of the ilish coincide with the monsoon season that starts in August. Monsoonal rains flood the rivers, making the journey easier. Females lay up to 2 million eggs each. The young hatch in about a day at less than a tenth of an inch long (around 2.5 mm). Their journey to the sea takes five or six months and they spend one to two years in the sea before making their own spawning run.
A traditional and much-loved food staple in the Bengali region, Ilish are a major part of the annual commercial fish catch there. They are normally taken in nets as they journey up and down rivers or in close coastal waters. Traditionally, ilish were not eaten between October and January so that most of the young reached the sea, but fishing now continues year round and some populations are becoming overfished. An increase in dams and other barriers to migration along the rivers is contributing to the population’s decrease.
