2 brood Katla fish found dead in Halda River: Experts suspect pollution, bacterial infection

Two dead brood katla fish were recovered from the Halda River yesterday (22 June), raising renewed concerns over water pollution and bacterial infection during the fish breeding season.

The recovery was made with the help of local residents by Sub-Inspector Ramzan Ali of the Ramdas Munshir Hat River Police Outpost in the evening.

With assistance from Rauzan Upazila Senior Fisheries Officer Alamgir Azadi, the two fish were sent to the Halda River Research Laboratory at the University of Chittagong for further examination. 

According to the initial report, the fish measured 38 inches and 36 inches in length and weighed 12.85 kg and 8.35 kg, respectively.

Similar incidents occurred last year, when as many as seven brood fish reportedly died in June. Experts suggest that brood fish - mature, egg-bearing fish - often become physiologically weak after releasing eggs, making them vulnerable to infections.

Dr Mazoorul Kibria, coordinator of Halda Research Laboratory, said, "One likely culprit behind the deaths is Aeromonas spp, an opportunistic pathogenic bacterium. These bacteria typically do not affect healthy fish but can seriously infect those weakened by stress or environmental changes. After spawning, brood fish suffer from hormonal imbalances and weakened immune systems, making them susceptible to such bacterial attacks."

"The problem appears to have been compounded by seasonal pollution. In recent days, sacrificial animal waste - such as hides and internal organs - was dumped into the Halda River. Additionally, heavy rainfall earlier this week brought runoff loaded with organic and industrial waste, significantly altering the river's color and quality,"he said. 

"These conditions have led to a spike in ammonia levels, creating a phenomenon known as eutrophication, which accelerates bacterial growth", he added.

He said, "Examinations of the dead fish revealed typical signs of Aeromonas infection: red ulcers and lesions on the skin, rotting fin bases, pale or necrotic gills, swollen abdomens, and bulging eyes [exophthalmia]."

"Based on these symptoms and recent environmental changes, we suspect that the brood fish died as a result of Aeromonas infection, triggered by sudden eutrophication and pollution in the river", Dr Kibria concluded.

The Halda River, known as the country's only natural breeding ground for carp species like katla, continues to face environmental challenges that threaten its biodiversity. Fisheries officials and environmental scientists have urged immediate action to prevent further contamination and protect the river's delicate breeding ecosystem.