Mother fish of various species released eggs in the Halda river for the third time this year on Thursday.
The river is South Asia's sole natural fish spawning centre.
On early Thursday night, the mother fish began releasing eggs when the tide rose with rain and thunder. However, there were relatively few collectors in the river at the time.
Around 500 people began collecting eggs in the morning with nearly 200 boats, Dr Manjurul Kibria, a Halda researcher and Chittagong University zoology department professor, said.
"There are a lot of eggs during high tide at night, but there aren't many at low tide."
The Halda researcher hoped more than twice the number of eggs will be found in the third phase than in the previous two phases.
On the morning of May 16, mother fish released eggs in the river in the first phase. The second phase of egg release takes place later that same night. The researcher said the number of eggs collected in the first two phases was very low this year.
Carp fish release fertile eggs in the Halda river at high and low tide during the full moon from mid-April to June of every year, when there are thunderstorms and heavy rainfall.
