A mother-son duo who ate poisonous puffer fish, locally called "potka fish", died in Khulna's Batiaghata upazila on Monday evening.
Pufferfish is considered a delicacy but can be fatal because of its toxicity, if not cooked properly.
The deceased were identified as Pori Begum, 60, and her son, Jahangir, 36, residents of Mathabhanga village in Batiaghata upazila.
Police said the poor family caught the fish from the Rupsha river and consumed it after cooking.
As they fell sick, neighbours took them to Khulna Medical College and Hospital where Pari Begum was announced dead on arrival. Jahangir died later during treatment.
Jahangir’s cousin Saidul, 35, who also consumed the fish is currently being treated for poisoning at the hospital, said duty doctor Bidhan.
Officer-in-charge of Labanchora police station, Md Enamul Haque, said the family was probably unaware of the toxicity of the fish.
The rate of poisoning due to pufferfish consumption is high in the rainy season in Bangladesh as this is the time when they get ready for breeding.
In Bangladesh, two species of pufferfish are found in freshwater environment and at least 20 species in rivers.