With NAQDA intervention:

Prawn farming industry ready for export market

By P. Krishnaswamy

Since the eighties the coastal areas of the Northwestern Province, stretching from Negombo to Chilaw, Palaviya, Kalpitiya, Puttalam and Wanathawilluwa remain the hub of the lucrative prawn farming industry. Crown lands and coconut groves were converted into ponds for prawn culture and even some paddy farmers converted their traditional paddy lands into ‘prawn ponds’ because they found that the profit level was several fold more compared to paddy cultivation.

Although the scenario with regard to the industry was seemingly not so bright in the recent years due unmanaged pond culture, resulting in the outbreak of viral and other diseases, the situation has considerably changed towards the positive upward trend with the intervention of the Government through the National Aquaculture Development Authority of Sri Lanka (NAQDA) and other authorities of the Ministry of Fisheries and Aquatic Resources Development.

Although there has been a diminishing trend in the export markets that have hereto been readily available in Japan, EU countries and the US, Director General of the NAQDA Nimal Chandraratne is of the view that this is only a transient phenomenon due to economic tidings in those countries after the world economic downturn, and that the situation would improve and there will be a demand for the Sri Lankan prawns because the quality is comparatively good. Even China has now started importing Sri Lankan prawns, he pointed out.

Quality being the main criterion, the potential for building up a sizeable export prawn market for our country is excellent. The present obstacle is the shortage of the supplies which can only be overcome by stepping up production. Sri Lanka being a tropical island with its abundance of brackish water offers ideal condition for increasing prawn production by aquaculture.

World prawn production has been in the increase in the past many years and Sri Lanka’s share of this lucrative market is quite negligible with a contribution of less than 0.2 percent. Shrimp farming has great potential to diversify and secure income in rural Sri Lanka.

Cultured shrimp production from 1990 to 2006 in Sri Lanka is as follows:

The brackish water area in Sri Lanka is estimated at about 120,000 ha of which 80,000 ha are estuaries and large deep lagoons. The rest comprises shallow lagoons, tidal flats and mangrove swamps. The smaller lagoons especially the Southwestern, South and Southeastern regions are mostly closed by the sand bar while some have connections with the sea for a short duration during the rainy seasons. Some of the large lagoons such as Puttalam, Jaffna and Negombo maintain their connection with the sea throughout the year. Large expanses of tidal flats and mangrove areas exist in Kalpitiya and Mannar regions. Out of the 120,000 ha of the total brackish water areas of the Island, about 6,000 ha have been identified as potentially suitable for shrimp culture.

The extent of areas suitable for shrimp culture in Sri Lanka

The second major disease outbreak was reported in 1996 which was confirmed as WSSV; the disease was first detected in Udduppuwa and Karukupane areas belonging to the zone of Arachikattuwa in the Northwestern Province.

The disease subsequently spread throughout the shrimp farming area in Northwestern Province. The total loss in foreign exchange earnings was estimated at Rs. 1,000 million and around 85 p.c. of total farm areas became non-functional due to this outbreak.

The Dutch Canal which has been the main source of water for shrimp farms has low carrying capacity now for shrimp farming with deteriorated water quality as farmers have been taking water from and discharging effluents into the same water source without proper treatments. The rapid spread of WSSV infections throughout shrimp farms on the Northwest coast was facilitated by the geographic location of main water sources.

The main lagoons that act as water sources and as effluent receiving waters for the shrimp culture industry are interconnected by the Dutch Canal. This forms a network facilitating the easy spread of disease over total farming area of the Northwestern province.

Thirty-one species of prawns have been recorded from Sri Lankan waters. Of these only the Penaeid shrimp have the commercial value. Metapenaeus dobsoni is the most abundant among those species that are found in broth estuarine and marine waters. Being one of the smallest in size M. dobsoni is however not as commercially important as less abundant species like P. indicus and P. semisulcatus. Due to faster growth, large size attained and export potential, the black tiger prawn, Penaeus monodon has been selected for the brackish water prawn culture in Sri Lanka.

Sri Lankan prawn culture industry experienced three major outbreaks of diseases. The first, in 1988 to 1989, was due to Penaeus monodon type baculovirus (MBV) infection. This resulted in a loss in 35-72 p.c. of production and the route of infection was thought to be importation of Pl from Thailand. Poor farming and hatchery practices, poor water quality with poor soil conditions were identified as the main contributory factors for the outbreaks of MBV.

The third major disease outbreak, reported in August 1998, was due to a dual infection of yellow head virus and white spot syndrome virus. The moribund shrimp with dual infection were first observed in the Karukapane and Uddappuwa areas and subsequently the mix infection spread to shrimp farms along both the Northwestern coast. It is believed that brooders smuggled by hatchery operators from other countries in mid 1997 to early 1998 were the principal route of introduction of YHV into Sri Lanka.

Paddle wheels were the main method of aeration on farms using aeration. Farmers usually used four paddle wheels per 0.4 ha of pond for 4-18 hours. Aeration increased with the increasing age of the shrimp, on cloudy and less windy days and at night. Ponds were built with mud banks and mud floor. The stocking seasonality is planned by NAQDA to achieve a minimum of two month period between two consecutive crops to allow the ponds to dry. Pond bottoms were dried until cracks appeared in the sediment layer.

The seasonal crop calendar was prepared by getting comments from a technical committee comprising experienced farmers representing farmer societies of different farming zones and NAQDA extension officers. Sri Lanka is a rural-based society which is looking to aquaculture to diversify rural incomes and reduce rural-urban migration. For example, its fisheries development plan for the northern province, where the fisheries sector collapsed due to LTTE terrorism and the tsunami of 2004, includes an important role of aquaculture development.

The Ministry of Fisheries and Aquatic Resources Development, under the direction of Minister Rajitha Senaratne, has now launched a pilot project in Kusaly in the Arachchkattuwa AGA division for the prawn culture of a new and significant species of prawn known as ‘Vannamai’ which is generally believed to withstand viral and other disastrous diseases.