Photo: NACA
Within the overall agro-based economy of the Bangladesh, the contribution of prawn (locally known as golda) production is important to its people for livelihoods, income and food supply, writes Nesar Ahmed of the Network of Aquaculture Centres in Asia-Pacific.
In 2006, Bangladesh exported 49,317 tons of prawn and shrimp valued at US$415 million, of which around 25% was contributed by prawn (DOF, 2007). This figure is expected to rise with the increasing expansion of freshwater prawn cultivation into new areas of Noakhali, Patuakhali, Pabna and Mymensingh districts. Prawn farming is mostly concentrated in southwest Bangladesh, mainly Khulna, Bagerhat and Satkhira districts.
The expansion of M. rosenbergii farming depends on availability of prawn fry, the supply of which is currently the main bottleneck for further expansion of prawn culture. The prawn culture sector in Bangladesh still relies on wild postlarvae (PL). Farmers prefer to stock wild PL rather than hatchery produced fry as production of the hatchery PL is limited and farmers consider them to be of lower quality. In addition, the survival of wild PL is much higher than that of hatchery produced PL (Ahmed, 2001). However, there is a growing acceptance of hatchery fry by producers.
Since the late 1980s, there has been concern over the effects of intensive fishing of prawn PL (Ahmed, 2000). Indiscriminate fishing of wild PL with high levels of by-catch (i.e. non-target species caught incidentally) and biodiversity impacts on the coastal ecosystem has provoked imposition of restrictions on wild PL collection (Ahmed 2003).
In September 2000, Department of Fisheries imposed a ban on wild PL collection. The rationale for the ban was to protect biodiversity from the harmful effects of intensive PL fishing in the coastal zone (DOF, 2002). However, the lack of alternative livelihoods for poor people engaged in PL fishing is one of the principal constraints on implementing such a ban.
Due to the scarcity of wild PL supply, a prawn hatchery sector has emerged over the last few years. However, the quality of hatchery PL remains a concern for prawn farmers. It is assumed that source of broodstock (i.e. mother prawns or berried females) is an important issue for producing quality fry in hatcheries. Hatcheries are currently unregulated with no quality assurance of broodstock.
One of the problems in regulating and managing the supply of brood to prawn hatcheries is the lack of information. At the same time, there is no information on the projected demand of broodstock by hatcheries. In response the Network of Aquaculture Centres in Asia-Pacific began a study to identify potential sources of broodstock and appropriate harvesting, marketing and transportation systems. Addressing these issues should lead to higher production of quality PL that will help to expand freshwater prawn farming into new areas of Bangladesh through developing and sustaining prawn hatcheries.
They concluded that despite strong demand of broodstock by the hatcheries there is no broodstock bank in Bangladesh. Due to the scarcity of wild broodstock supply to the hatcheries, it is urgently needed to establish a broodstock bank in prawn farming areas.
To meet a part of immediate demand for quality broodstock, both the public and private sector should come forward to establish their own broodstock banks. Hatcheries could be linked to the public and private broodstock bank to ensure the availability of quality broodstock. It would also necessary to encourage private entrepreneurs to start commercially producing good quality broodstock.
Rearing broodstock of good quality requires special techniques and fresh spawns from the nature. Improving the quality of broodstock will result in better quality spawns, reduce mortality rate and increase productivity. However, concerns may arise about the sustainability of broodstock banks in terms of technical, biological, environmental and economic aspects.