Black gold in Pangasius ponds

In Bangladesh, SEAT’s activities are being coordinated by Bangladesh Agricultural University (BAU). Here, researchers  are studying Penaeid shrimp, freshwater prawn, tilapia and Pangasius value chains. As part of SEAT’s action research, the development of a value chain and commercial opportunities for Pangasius pond sludge was identified as an important issue. Below, Dr. M. Mahfujul Haque describes SEAT’s investigations into this sludge and it’s possible uses in helping communities grow crops.

Striped catfish Pangasius (Pangasianodon hypophthalmus) was introduced in early 1990s from Thailand and is known locally as Pangas, a fast growing species and it is in high demand among across the range of social classes of people in Bangladesh. Between 2010-2011, it was estimated that total production of Pangasius in Bangladesh was as high as 300,000-400,000 MT! The majority of the fish are produced in culture systems developed in earthen ponds and Pangasius now represents the main intensive form of aquaculture in Bangladesh. One of the reasons for this is that the stocking density and productivity of Pangasius, are much higher than for other species traditionally produced in Bangladesh so farmers can produce more fish per hectare. However, such a large amount of fish being produced requires a lot of feeding and the total amount of feed used has been estimated to be as high as 100,000-120,000 kg/ha/year, resulting in significant amounts of waste (15-20 cm over 2-3 year period) that builds up as sediment in the ponds.

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In a previous research, feed and sediment based analysis showed that nitrogen deposited in a hectare pond could be as much as 17,527 after 2 years. The sludge is an excellent source of organic Nitrogen in the form of urea from the Pangasius themselves and the economic implications become clear when it is realised that the price of an equivalent amount of urea is more than BDT 300,000 (US$ 4000)/ha. This mean that catfish pond sediment is a mine of urea resembling black gold! Although farmers are reluctant to remove this nutrient-rich sludge due to labour costs there have been encouraging results with bag gardening in a pilot experiment in Pangasius producing areas.

Having demonstrated Pangasius sludge’s use as a fertiliser, bag gardening was introduced to a saline affected coastal community, Dhalbaria, Kaligonj, Satkhira.  The salinity of the land, means people cannot grow any vegetables or other plants. Households in affected land areas were given dried Pangasius pond sludge in bags made from Pangasius feed bags by professional women who make shopping bags. The household women were also given demonstrations and chilli plants for growing in the bags. Two months after transplantation the chillies could be harvested!

Initially, during the distribution of the bags, women were not interested in receiving them because their previous experience growing plants in the salinity-affected plots was that it was a fruitless task. After households started to have success, some were using leftover shrimp post-larvae containers, made of cork-sheets, rather than converted Pangasius feed bags to hold the growing medium. These experiences show the potential to develop a value chain of Pangasius pond waste as a growing medium for edible plants.

An enterprise development organization in Bangladesh, Practical Action, have been using the action research of SEAT to promote Pangasius sludge-based gardening in urban areas of Bangladesh. The have demonstrated Pangasius sludge based bag gardening with two social classes of people (slum dwellers and urban elites) in the capital city Dhaka. In both cases, successful results of producing chillies in the bag and adoption, were encouraging.

There have been however, some questions: in terms of sludge quality (e.g. any chemical contamination), types of suitable vegetables to grow, bag durability and bag design etc. An action research investigation has been started with the leading taken by the University of Copenhagen to analyse the chemical composition of Pangasius pond sludge in detail. This will lead to the development of a value chain for Pangasius sludge to be used commercially as a growing media.

Photo © Loni Hensler