Three species of the Indian major carps,catla (catla catla), mrigala ( cirrhinus mrigala) and rohu (labeo rohita), spawn in the lower Halda River , a tibutary to the Karnafuli River near the city of Chittagong, Bangladesh(Fig.1).This spawning ground is the richest in Bangladesh and has long been the major source of naturally produced carp fry for pond culture in much of this countr. Some of them have been exported to India. The production was about 252 million fry in 1974 ( Ali, et al. 1974),genarating approximately 1.5 million taka (Tk. 15.00 equals $1.00).
Located at the oxbow - bend of the river, this is the only reported spawning ground of major carps in a freshwater tidal zone. It is unlike other riverine major carp spawning grounds which are usually found in flooded nullah ditches and paddy fields (Khan 1924; Dubey and Tuli 1961 ), shallow water pockets (Mookerjee 1945 ), interlocking channel systems (David 1959) and flowing rivers without tidal influence (Job and Chacko 1948). This unique spawning ground of the carps in the Halda River has not been investigated in detail, and factors that determing timing, location , migration and brood stock origins and extent remain unknown.
The Halda Rive emerges from the north-ern hill region of the Chittagong district of Bangladesh. In the upstream region there are three major tributaries, Dhurang, Talpari and Sarteakhal.