By Partha Bandyopadhyay and Sanjeev Bhambi
The immense scope for scampi farming in India is being threatened by diseases. A lack of awareness on culture management techniques and poor quality seed is being blamed.
In India, a spurt in freshwater prawn farming activities can be seen in recent years. The giant freshwater prawn (Macrobrachium rosenbergii de man, 1879), popularly called the scampi in India, is an important commercial species. It is a source of food supply as well as a valuable export commodity. This freshwater prawn is distributed mainly in the eastern and south-eastern regions, where environmental conditions are most favorable for its growth. Increasing demand of this species in the domestic and export markets has resulted in farmers enthusiastically culturing the scampi at high stocking densities and intensive feeding. Culture has also expanded to rice fields.
India produced 54,230 tons of the popular freshwater prawn variety, standing at third position after China and Vietnam, which produced 128338 and 28000 tons respectively in 2004 - 05. But the production totaled 40000 tons in 2005 - 2006 and this declined to 20000 tons in 2007 - 2008. (Thampi Sam Raj, 2008).
Scampi culture has been extended to the coastal areas of India. As black tiger shrimp culture faced a variety of problems, the focus shifted to the scampi. Efforts are now being made by the marine products export development authority(MPEDA) which has identified it as a trust area for increasing production of high value-added products and creating employment opportunities.
However, during the season (March - November 2008), production has been declined due to disease outbreaks. Industry representatives blame this on the lack of good quality post larvae. Unable to handle disease outbreaks, farmers are shifting to agriculture and some in southeast of India have shifted to paddy or sugarcane farming. Whilst those who opted for paddy cultivation may return to scampi culture after a few months when the situation improves, those who have opted for sugarcane cultivation will have their fields unavailable for at least three years.
The main reason is that farmers are not able to source disease free post from hatcheries. Despite the obvious advantages with scampi farming, insufficient effort has been put into developing scientific culture systems or domesticating brood stock(figure 1) for quality post larvae production. Currently, brood stock are often selected from culture ponds of farmers which are often subjected to stressful conditions and may not be the best source of healthy seed stock.
It has been reported that viral pathogens cause severe losses to the scampi culture sector and mortality due to the viral pathogen, macrobrachium rosenbergii nobavirus (MrNV) can reach 100% within two or three days in the hatcheries and nursery ponds. The loss has been estimated at several millions of dollars.
Recently, a new disease with unusual clinical signs has been reported in the major scampi culture area in nellore district, Andra Pradesh, which has been named as appendage deformity syndrome (ads figure 2). Ads have affected more than 80% of culture ponds in nellore district. It has reduced the culture area to about 20,000 acres (8,813 ha) from more than one lakh acres (100,000 acres/44,069 ha). Prawns infected by ads have bent or deformed rostrum, antennae cut beaded or corrugated appearance of antennules and which are more prone to beakage, corrugated appearance of the carapace, poor growth and varying mortality rates. Scampi can be infected after 1-2 months
Of stocking of juveniles in the culture ponds and infection is more pronounced during 4-5 months of culture. This type of disease or clinical sings has not been reported in any other country. The area has also recorded poor rainfall during the last three years.
In the eastern part of the country, mainly in West-Bengal, white tail disease (WTD) has affected scampi. Two different sized particles, both developing in the cytoplasm of target cells, are found associated with disease animals. WTD is responsible for mortalities in hatcheryreared scampi and causes significant economic losses. The disease was first reported in the eastern part and subsequently in southern parts of the India.
Beside this, is a very common and harmful disease, Sessilinasis (figure 3) caused by a number of pathogens including Zoothamnium spp., Vorticella spp., Carchesium spp, Epistylis spp, Gastonauta spp. And Intranstylum palaemoni all of which belong to Peritrichia family. Sessilinasis and scampi are symbionts. Once infected, cotton wool-like growth appears and rotten which reduces its respiration and excretory capacity and making feeding difficult. This disease was more serious during the last rainy season. Losses are huge from bad quality harvests.
Other diseases encountered were 'back spot' (figure 5) and 'blue shell disease' (figure 6) which are causes by bacteria (figure 7) and blue green algae that break down the outer skeleton. Usually it follows physical damage and can be avoided by careful handling. At other times, algae or insect eggs may be present on the shell. This condition is not a disease, but rather an indication of slow growth and is eliminated when the scampi moults.
The limitations in supply of quality seed, the intensive farming methods used and the lack of awareness of better management practices among farmers have made it difficult for the scampi farming industry to realize its full potential. What are required are proper farm and water quality management and intensive attention to the health of the animal and the development of specific pathogen free(SPF) stock. Only then can the scampi become a major food commodity and source of income for India's aquaculture industry.
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