Ilish

The ilish, scientifically known as *Tenualosa ilisha*, is a highly valued species of fish in the family Clupeidae. It is closely related to the herring and is famous throughout South Asia for its oily and tender texture. This fish holds immense cultural and economic importance in the Bengal region. It serves as the national fish of Bangladesh and the state fish of West Bengal, India.

Because of its popularity, the ilish is a major driver of trade and employment in many coastal areas.

This species is anadromous, which describes a specific life cycle involving both salt and fresh water. The fish primarily lives in marine environments but migrates into freshwater rivers to spawn, or lay eggs. During the southwest monsoons, which occur from June to September and January to April, the fish ascend rivers for approximately 50 to 100 km. After the spawning process is complete, the fish return to the sea. In Bangladesh, the small juveniles that remain in the rivers are known as jatka.

To survive, the ilish uses a specialized feeding method called filter feeding. It forages along muddy bottoms to find its food. The fish uses gill rakers, which are fine, comb-like structures located on the lower part of the gill arch, to strain nutrients from the water. There are between 100 and 250 of these rakers on each arch. The diet of an adult ilish consists mainly of Bacillariophyceae, known as diatoms, and Chlorophyceae, or green algae. Juvenile fish rely more heavily on crustaceans, such as Copepoda and Cladocera, to grow.

Physically, the ilish shows distinct differences between males and females. Females generally grow larger, reaching lengths of up to 55 cm, while males typically do not exceed 46 cm. Maturity is reached within the first or second year of life. Males reach maturity at a size of 26–29 cm, whereas females mature at 31–33 cm. The fish has 18 to 21 dorsal and anal soft rays but lacks dorsal spines. Its belly is covered by 30 to 33 scutes, which are bony plates. While alive, the silver body of the fish often shows flashes of gold and purple.

In terms of global production, Bangladesh is the leading producer of ilish. As of 2023, approximately 97% of the world's total ilish supply originates in Bangladesh. This single species contributes about 12% of the total fish production in the country. The economic impact is significant, accounting for about 1.15% of Bangladesh's GDP. The industry supports the livelihoods of about 450,000 people directly through catching the fish. Additionally, around four to five million people are involved indirectly in the trade, including transportation and marketing.

Conservation efforts have been vital to maintaining these numbers. Due to declines caused by pollution and overfishing, the Bangladeshi government imposed a ban in 2002. This ban protects both brood hilsa and the juvenile jatka. They also introduced fishing bans during the specific breeding seasons. These measures have been successful in Bangladesh, where the catch increased by 8–10% annually up to 2021. This is a notable contrast to ten other hilsa-producing countries where production has declined.

Culinary traditions surrounding the ilish are incredibly diverse. In Bengal, a famous preparation is Shorshe Ilish, which uses mustard seed paste. Because the fish is naturally oily, it requires very little additional oil during cooking. In the Andhra Pradesh region of India, the larger mature fish are called pulasa. These fish are highly prized in the Godavari districts, where they are sometimes called the "king of fish." In Pakistan, the fish is known as Pallo Machi and is a staple of Sindhi cuisine.