Fishermen depressed as salinity, heat jeopardise carp egg breeding in Halda

This is the peak breeding season of carp fish. Over the past 20 days, hundreds of fishermen have gathered along the banks of the River Halda – the sole natural breeding hub for carp fish in the country, eagerly awaiting the collection of fish eggs.

However, their hopes have been dashed as the river appears to be devoid of eggs, despite the passing of two crucial egg-laying periods in May. The absence of even sample eggs from the mother fish has left the fishermen perplexed.

Researchers attribute this unfortunate circumstance to a combination of factors.

Ongoing high temperatures exacerbated salinity levels resulting from climate change, and insufficient rainfall accompanied by thunderstorms have all contributed to an unfavourable environment for successful egg hatching in Halda. Consequently, the wait for the coveted eggs continues to extend.

Mohammad Shafi, president of Halda Egg Collectors Association, said since the first week of May, hundreds of fishers have been waiting to collect eggs in Halda with their boats and various equipment. The hatcheries are ready for hatching the collected eggs. 

"Many bought nets and boats with loans. But if fishers do not get eggs at peak season, they face huge losses. In the last two years, eggs were damaged due to salty water entering Halda during the breeding season," he added.

Every year from Chaitra (March-April) to Asharh (June-July), the River Halda experiences heavy rainfall accompanied by thunderstorms. During this period, the river's water flow intensifies, causing it to turn muddy and foamy, thus creating favourable physicochemical conditions for egg breeding.

However, the increased salinity and high temperatures have disrupted the hormonal balance of the mother fish in the Halda, leading to a continuous decline in egg production, as stated by Halda researcher Shafiqul Islam.

A study done by Shafiqul Islam showed that the average water temperature in Halda water in the first week of May was 34.5 degrees Celsius while the ideal temperature for carp breeding is 20-30 degrees Celsius. Besides, in the first week of May, the salinity level in Halda water increased to 2 ppt from 1.5 ppt last month. 

Moreover, the electrical conductivity in Halda water increased to 620-4,000 micro Siemens which was 379-3,013 in the third week of April. But, the ideal value is 350 micro Siemens for fish breeding.

"Due to climate change-induced high temperatures, and increased salinity in river water, the breeding cycle time of carp-like fish in Halda is increasing and their reproductive capacity is decreasing," he added. 

Manjurul Kibria, Halda researcher and Zoology Department professor of Chittagong University (CU), said, "The third breeding period of this season is going on. But mother fish are not breeding eggs." 

The natural topographies of the river have been destroyed and the water temperature is increasing due to the construction of retaining walls and blocks on both banks, he claimed.

The fourth period of breeding by mother fish started on 16 May and will continue till 21 May. The next period will be from 1 to 6 June and the last period of this season will be from 15 to 20 June.

"If there is enough rain with thunderstorms and if the river sees an onrush of water from upstream, there is a possibility of breeding by mother fish," said Halda researcher Mohammad Ali Azadi, former professor of Zoology at Chittagong University. 

Harun-or Rashid, the forecaster of the Patenga Meteorological Office, said there are storms, hail, and thunderstorms in Chattogram which will continue till 24 May.