Browsing by Author "Verreth, Johan A. J."
Identification of stressors that affect white spot syndrome virus (WSSV) infection and outbreak in pond cultured Penaeus monodon. EA Tendencia & JAJ Verreth -
The Israeli Journal of Aquaculture-Bamidgeh, 2011 - The Society of Israeli Aquaculture and Marine BiotechnologyWhite spot syndrome virus (WSSV) has been a big problem to the worldwide shrimp industry. Exposure to stressors related to physicochemical water parameters affect WSSV infection but not all WSSV infections result in outbreaks. This paper describes a detailed monitoring of important physicochemical water parameters on a farm with 11 ponds that had WSSV infection. The virus was detected in shrimp exposed to two or more simultaneous stress factors (temperature, pH, water level) or multiple stressors for a number of days. Exposure to more than three stressors resulted in an outbreak of the disease within 3-6 days. Outbreaks were experienced in ponds with a temperature of 26-27°C, a pH lower than 8.0, pH fluctuation of 1.0, and a water depth of less than 1 m. Shrimp stocked in eight of the ponds were successfully harvested after 128-173 days of culture.
Temperature fluctuation, low salinity, water microflora: Risk factors for WSSV outbreaks in Penaeus monodon. EA Tendencia & JAJ Verreth -
The Israeli Journal of Aquaculture-Bamidgeh, 2011 - Society of Israeli Aquaculture and Marine BiotechnologyWhite spot syndrome virus (WSSV) has been devastating the shrimp industry for almost a decade. This study compares water parameters, alkalinity, and microflora in three ponds on a farm on Negros Island (Philippines) during two production cycles where WSSV infection resulted in an outbreak in 2006 but not in 2005. The total bacterial count of the pond water in 2005 was about twice as high as in 2006. However, luminous bacterial counts were twice as high in 2006 than in 2005 and total presumptive Vibrio, as counted on Vibrio selective thiosulfate citrate bilesalt sucrose (TCBS) agar, was over ten times higher, with a greater percentage of green colonies. More green colonies might indicate a higher concentration of harmful Vibrio bacteria. Total alkalinity for both production cycles was within the normal range while temperature, salinity, pH, and dissolved oxygen varied and sometimes fell below or exceeded the acceptable range. In 2006, there were more instances during which the temperature fluctuated 3-4°C within the period of 07:00-17:00, and salinity more often dropped below 15 ppt. Our survey suggests that WSSV outbreak are triggered by water temperature fluctuations of 3-4°C, coupled with low salinity and a high presumptive Vibrio count
WSSV risk factors related to water physico-chemical properties and microflora in semi-intensive Penaeus monodon culture ponds in the Philippines Whitespot syndrome virus, WSSV, is the most important among the shrimp diseases. One of the suggested WSSV risk factors is the occurrence of stress since stressors could compromise the shrimp defence system thus increasing the risk of WSSV infection. Stressors are usually related to the physico-chemical properties of both water and pond bottom. This paper investigates the effect of some biotic and abiotic components of the pond ecosystem on WSSV infection and outbreak. Water physico-chemical properties and microflora of 91 production cycles of 8 semi-intensive shrimp farms were analyzed to determine WSSV risk factors, using factor analysis and logistic regression. Fluctuations of temperature and pH are important risk factors that will result to an infection but not necessarily to an outbreak. Exposure to high salinity and high temperature are important factors for an infection to result to an outbreak. The risk of an infection is reduced when the water temperature is high, salinity fluctuations are small, and percentage of yellow Vibrio colonies is greater than the green ones. Further studies are needed to clarify the effects of water depth, water transparency, and various bacterial counts; these factors could be individual or interactive.