Longitudinal disease studies in small-holder black tiger shrimp (Penaeus monodon)
farms in Andhra Pradesh, India. I. High prevalence of WSSV infection and low
incidence of disease outbreaks in BMP ponds
A longitudinal study was conducted from January to August 2005 in small-holder black tiger shrimp (Penaeus
monodon) ponds in the West Godavari District of Andhra Pradesh, India (16°25′ N, 81°19′ E). The study
involved 457 ponds owned by low-income farmers participating in a better management practice (BMP)
programme. Disease outbreaks occurred in 16.6% of ponds. There was significant spatial clustering of disease
outbreaks with 31 (40.8%) of the 76 recorded disease outbreaks occurring in a single village block. Bivariate
analysis indicated a 1.6-fold higher likelihood of disease outbreaks from nursery-stocked ponds but this was
not significant in multivariate analysis due to the confounding effect of pond location. There was evidence of
increasing prevalence of WSSV infection during grow-out. WSSV was detected in 5.9% of 119 batches of
postlarvae tested at stocking, 38.2% of 34 juvenile batches collected at the time of transfer to grow-out ponds,
and 47.0% of 336 pond stock tested at normal harvest or crop failure. WSSV was detected in 43 of 59 (72.9%)
disease outbreak ponds tested and 115 of 277 (41.5%) non-outbreak ponds tested. Heavy WSSV infection was
detected at harvest in 116 of the 336 (34.5%) of the ponds tested, including 78 ponds for which no outbreak
was recorded. Duration of crop was recorded for 431 ponds with a mean of 117.0 days and a range of 20 to
176 days. Median duration was significantly shorter for disease outbreak ponds (68.5 days) compared to nonoutbreak
ponds (119.0 days). Duration of crop also varied according to WSSV detection levels at harvest, with
median duration for ponds classified as heavy WSSV infection (108.5 days) significantly shorter than for
ponds classified as either light WSSV infection (116.0 days) or WSSV-negative (116.5 days). The study
indicated a high risk of WSSV infection during grow-out but a relatively low incidence of disease despite a
high prevalence of heavy WSSV infection in non-outbreak ponds