Natural carp breeding in Kaptai Lake

Rangamati's 700-square-metre Kaptai Lake once teemed with fish but for many years naturally occurring fish stocks have been in decline. For more than a decade researchers thought this was because the relatively shallow waters in key parts of the lake were preventing carp from breeding. A new ongoing study into the lake's fish stocks however, has already returned a surprising result: in some areas carp still reproduce.

Three scientists, Mohammad Abul Bashar, Kazi Belal Uddin and Sanjeeb Basak of the river research substation of the Bangladesh Fisheries Research Institute began the investigation into natural fish reproduction in the lake on 21 June 2016.

“On June 2,  we were able to collect carp eggs from Mastan Tila near the reserve forest ghat in Longudu upazila,” says one of the scientists, Belal. “We collected five kilograms of eggs.”

Researchers have since discovered more active breeding grounds. “Carp are breeding in Kachalong, Karnafuli, Chengi and Rengkhong channels,” says Abul Bashar. “It's quite a surprise since both the first study conducted in 1986 and the second in 2004 cast doubt on the lake's ability to support carp reproduction. It was thought decreased navigability had destroyed the breeding grounds.”

The findings leave the scientists hopeful of a brighter future for fish stocks, as long as the use of natural fish traps, locally called 'jak,' can be properly controlled. “If operations against the use of jak continue,” Abu Bashar says, “it is likely the lake can regain its former glory as an abundant source of fish.” Kaptai Lake was once one of the largest sources of freshwater fish in the country.

The precise species of carp eggs collected on 11 June from Kachalong Channel meanwhile is yet to be identified. “The lake is home to 75 fish species,” says Abul Bashar, “which includes four carp species. Carp prefer to breed at times of heavy rainfall and during thunderstorms when currents and waves are strong.” According to the scientists the first carp eggs of each season can be expected to be mature by early May, with reproduction continuing through to early July.

Manager of the Rangamati office of the Bangladesh Fisheries Development Corporation Mohammad Asaduzzaman says the results indicate that initiatives taken by the corporation to combat the use of jak traps are working. “Bans on fishing are helping to protect the breeding fish,” he says.