The Halda River in Chattogram’s Raozan and Hathazari areas is one of the largest natural breeding grounds for fish in South Asia.
Usually, fish release eggs into the river just ahead of the monsoon season, when conditions are favourable. Before laying all their eggs, female carp are known to release a few at first to test conditions.
These test eggs were laid in the river early on Wednesday night, but the high level of saltwater intrusion due to a combination of limited rainfall in the area and the effects of Cyclone Yaas substantially reduced the number released by the fish subsequently, experts say.
Fish egg farmers were dismayed after searching the river all day on Wednesday. It was Wednesday afternoon before they located the test eggs. It wasn’t until 12:30 am on Thursday that fish began laying eggs in earnest.
Approximately 1,500 fish farmers on nearly 350 boats attempted to collect eggs at the time. They finished up around 7 am.
Kamal Saudagar says that fish eggs were found upstream in the river near Garduwara, Noyahat, Azimer Ghat, and the Porakpali Sluice area, but little was found downstream.
“The fish laid their eggs during low tide last night,” he said. “But there is a lot of salt in the water, so they only laid a few eggs. If there is another storm tonight, they might release more eggs.”
Other fish farmers also found success in collecting eggs in parts of Hathazari and Raozan in the Ankuri Ghona, the mouth of the Kagatia, the Ram Das Munshi pier, Machua Ghona and Sattar pier areas.
Carp fish lay eggs from mid-April to June when rain, mountain runoff and the tide create the appropriate temperature and salinity, says Kamal Saudagar.
This season, the river’s salinity was affected by the smaller than usual amount of rain or runoff, the limited amount of water released from the Kaptai dam and the cyclone.
“These aren’t the regular conditions for breeding,” Chittagong University Department of Zoology Prof Manzoorul Kibria told bdnews24.com. “Yaas has raised the salinity of the river to 72 times the regular level!”
Prof Kibria described the yield of fish eggs collected as ‘fine’.
“They were able to collect a comparatively good number of eggs in the Azimer Ghat, Gurduwara and Machuaghana areas. But we are still collecting data and we will only be able to tell how many eggs were collected after we compile it.”
“The number of eggs isn’t even close to regular levels,” said Hathazari Upazila Nirbahi Officer Md Ruhul Amin. “Egg collectors are dismayed. The eggs they did get have been sent to the hatcheries and they have begun to hatch.”
The cyclone hit around the time of the full moon, which meant that a lot of saltwater entered the Halda River at high tide, Md Ariful Islam, a superintending engineer with Chattogram WASA.
The salinity level in the water rose to 3,100 mg per litre. The acceptable level for coastal areas is usually 600 mg per litre and the safe level in drinking water is 10 mg per litre.
“If we don’t get water from Kaptai, the salinity of the Halda will continue to rise,” Islam said. “We have to think about how much saltwater is intruding. And we have to think broader than a single day. We have to take the Karnapahuli River into consideration too. Most of the water that WASA takes from the Halda comes from the Karnaphuli. It is also necessary to dredge Kaptai Lake.”
According to Chattogram fisheries officials, last year about 25,500 kg of eggs were collected from the Halda River during this season last year, the highest amount since 2006, when farmers collected 32,724 kg.
The 10,000 eggs laid on May 25, 2019, produced 200 kg of fry, which was sold at a market price of Tk 80,000 per kg, for a total market value of Tk 16 million.