Monodon Slow-Growth Syndrome (MSGS) is a phenomenon appearing on cultured Penaeus monodon which grow abnormally slow and with irregular sizes in one pond.

To distinguish stunted growth caused by Monodon baculovirus(MBV) or Hepatopancreatic parvovirus (HPV), the Thai researchers have come to a common consensus on the definition of a MSGS pond as follows (Withyachumnarnkul, 2005; Sritunyalucksana et al., 2006),

1. Coefficient of variation (CV) of weight ≥35%.

2. Free from HPV infection or any other hepatopancreatic infection.

3. Appearance of any three of the following characters.

• Unusually dark color
• Average daily weight gain of less than 0.1g/day in 4 months
• Unusually bright yellow markings
• Bamboo-shaped abdominal segments
• Brittle antennae

Since 2001, the black tiger shrimp farmers in Thailand found an unusual retarded growth of their crops. The farmed P. monodon reach an average size of 12.5g instead of the regular size of 24 to 40g after 4 months of culture (Withyachumnarnkul, 2005). This problem made the farming unprofitable and caused great damage to the shrimp industry as the production value of farmed P. monodon was dramatically drop to 68% in year 2002 from 2000 (Chayaburakul et al., 2004).

This crisis doesn’t seem restricted in Thailand while, recently, our Indian customers reported that several farms are revealing slow growth of black tiger shrimp. After 4 months of culture, about 30% of the shrimps grow to 6g against the normal size at 30g. Case of growth retardation also had been found in one commercial P. monodon farm in East Africa in 2004 (Anantasomboon et al., 2006). Whether the phenomenon of these 2 cases is MSGS remains unknown. The circumstance in East Africa didn’t fit the criteria of MSGS definition when the mean body weight of the shrimps was only 30% below the normal ones.

Scientists in Mahidol University, Thailand have been pursued the cause of MSGS for years. Considering MSGS is nationwide, environmental factors such as salinity and weather as well as farming practice were roughly ruled out. As to seed and brooder, they are unlikely to lead to the problem whereas hatchery practice didn’t change during that period of time and genetic inbreeding would be a gradual progress, not arise so fast. Pathogen could be a reasonable suspicion (Chayaburakul et al., 2004).
After a series of diagnosis by PCR (or RT-PCR), histological methods, and electron microscope, no clear evidence have been found to link MSGS with known pathogenic viruses (Chayaburakul et al., 2004; Anantasomboon et al., 2006).

A new found RNA virus, Laem-Singh virus (LSNV) which was first addressed in 2006 could be associated with MSGS (Sritunyalucksana et al., 2006; Pratoomthai et al., 2007). In the beginning, researchers found that LSNV can be detected in lymphoid organ and gill of shrimps from both MSGS ponds and non-MSGS ponds, thus it was not regarded as a possible pathogen (Sritunyalucksana et al., 2006). However, a specific infection of LSNV in the fasciculated zone and onion bodies of Bellonci organ of the eyes of MSGS shrimps suggests that MSGS could cause by LSNV infection in specific tissue of P. monodon (Pratoomthai et al., 2007). So far, the relation of LSNV and MSGS remains to be demonstrated by bioassay with LSNV although a bioassay with lymphoid organs extracts had proved that the causative agent should exist (Withyachumnarnkul, 2005).

Reference

1. Anantasomboon G, Sriurairatana S, Flegel TW, Withyachumnarnkul B (2006) Unique lesions and viral like particles found in growth retarded black tiger shrimp Penaeus monodon from East Africa. Aquaculture 253:197–203
2. Chayaburakul K, Nash G, Pratanpipat P, Sriurairatana S, Withyachumnarnkul B (2004) Multiple pathogens found in growth retarded black tiger shrimp Penaeus monodon cultivated in Thailand. Dis Aquat Org 60:89–96
3. Pratoomthai B, Wongprasert K, Flegel TW, Withyachumnarnkul B (2007) Infection by Laem-Singh Virus in the fasciculated zone and organ of Bellonci of the eyes of small Penaeus monodon from Monodon slow-growth syndrome pond. Asian-Pacific Aquaculture 2007 -Meeting Abstract
4. Sritunyalucksana K, Apisawetakan S, Boon-nat A, Withyachumnarnkul B, Flegel TW (2006) A new RNA virus found in black tiger-shrimp Penaeus monodon from Thailand. Virus Res 118:31–38
5. Withyachumnarnkul B (2005) Search for solutions for MSGS in farmed black tiger shrimp. AQUA Culture AsiaPacific Magazine 1(4): 14–15