Relationship between white
spot syndrome virus and indicators of quality in Penaeus monodon
postlarvae in Karnataka, India
F. Corsin, P.C. Thakur, P.A. Padiyar, M. Madhusudhan,
J.F. Turnbull, C.V. Mohan, N.V. Hao, K.L. Morgan-2003
Diseases of Aquatic Organisms, 54(2): 97-104
Abstract:
White spot disease (WSD) is a viral disease of shrimp
caused by white spot syndrome virus (WSSV). Stocking WSSV-infected seed has
been implicated as a major risk factor for outbreaks of WSD. In addition,
the quality of postlarvae batches has been proposed as a predictor for good
crops. This paper describes the relationship between indicators of quality
and WSSV in postlarvae (PL) of Penaeus monodon from Karnataka, India,
over the period September 1999 to January 2000. Three outcome variables were
considered: the WSSV status of the PL, as determined by PCR, and 2
subjective assessments of PL quality, namely the activity of the PL and the
quality of the PL as determined by research assistants and farmers,
respectively. Of the 73 batches of PL, 49.3% from a random sample of farms
tested positive for WSSV. After adjusting for confounding, stocking earlier
in the growing season and duration of transportation were the main risk
factors for the presence of WSSV. The quality assessed by farmers and the PL
activity assessed by research assistants showed only fair agreement (kappa
0.252) reaffirming the subjective nature of such techniques. The only
variables consistently associated with either assessment of quality in
univariate analysis were PL length, number per bag and salinity of the water
in the delivery bags. After adjusting for confounding, no single variable
was consistently associated with PL quality and activity. The research
assistants' assessment of PL activity was also associated with the hatchery
and a brown-orange hepatopancreas in univariate analysis. After adjusting
for confounding, a brown-orange hepatopancreas was still significant and
fitted into the model together with the salinity of the water in the PL
bags. The farmers' assessment of quality was associated with PL length, date
of stocking and duration of transportation in both univariate and
multivariable analyses. There was no relationship between quality assessment
and WSSV in PCR-positive PL.