Ten years ago Bangladesh’s rivers were deeper and hilsa plentiful. Silting, dams and pollution pushed the fisher into deep ocean leading to shortage and a ban on export to India in 2006. The Bangladesh fish wholesaler's loss became Gujarat's gain as increasingly hilsa from the Tapti and the Narmada feed the Kolkata market. Though people say the Gujarat hilsa tastes bland in comparison, the delectable fish from the Padma costs at least 500 rupees more. Kaushik Das Gupta travelled to Bangladesh to report on the hilsa's shifting homebase