The assault took place during a drive to implement the two-month ban on catching, selling and transporting of Hilsa that began on March 1.
Sajib Das, the upazila fisheries officer, said a taskforce of river police and fisheries officer, led by UNO Ferdousi Begum, went to the area around 9pm after being tipped-off about Hilsa trading.
As soon they reached the spot, fishermen and fish traders, led by one Azgar Sardar, attacked them and held the UNO hostage, Sajib said.
Haimchar Union Parishad Member Rehan Golder said they went to the spot with UP Chairman Shahadat Sarkar after learning about the incident and rescued the UNO at 10pm.
They also detained Azgar and handed him over to police.
A two-month ban on catching, selling and transporting of Hilsa began on March 1 in six sanctuaries in the country which will be lifted on May 1.
The six sanctuaries are- 100 km in the Meghna River from Chandpur’s Shatnol to Laxmipur’s Char Alaxandar, 90km in Shahbazpur Channel in Bhola, 100 km in Tentulia River in Bhola, 40 km in Andharmanik River in Patuakhali, 20 km at lower Padma (Padma confluence) in Shariatpur, and 83 km in the Meghna River (from Hizla to Mehendiganj) in Barisal.