Prevalence and effect of
spawner-isolated mortality virus on the hatchery phases of Penaeus
monodon and P. merguiensis in Australia
L. Owens, C. McElnea N. Snape, L. Harris, M.
Smith-2003
Abstract:
Spawner-isolated mortality virus (SMV) has been
associated with mortalities in broodstock of Penaeus monodon and with
mid-crop mortality syndrome on grow-out farms. Epidemiological evidence
suggested an association between the SMV status of broodstock and subsequent
survival of their progeny, and this paper describes investigations into that
association. The faeces of 909 broodstock in 9 different groups were tested
by a polymerase chain reaction (PCR) for SMV and positive results were
confirmed by an internal dot-blot. Seventy-seven spawners (8.5%) were
positive for SMV with prevalence ranging from 0 to 24% among groups. The
prevalence in spawners of P. monodon was higher (24%) than in P.
merguiensis (4%). Three longitudinal studies were undertaken to compare
the survival of progeny from broodstock that were positive to SMV with those
that were not. Survival in hatchery tanks of progeny from SMV-positive
spawners was lower than those from SMV-negative spawners with reductions of
23% (p = 0.01), 7.3% (p = 0.214) and 18.9% (p = 0.129) in the 3 studies. The
conclusions were less consistent when examined during each of the later
stages of growth in hatchery pools, nursery and grow-out ponds, with progeny
from SMV-postive spawners sometimes having better survival rates. However,
survival was better overall in progeny from SMV-negative spawners. Simple
linear regression showed survival was negatively related to the proportion
of postlarvae from SMV-positive spawners, with a decrease in survival of
5.6% for each 10% increase in the proportion of postlarvae coming from
SMV-positive spawners (p = 0.006). Data from 38 ponds showed 6.71% of losses
were due to SMV. If these losses were consistent across the entire industry,
the annual loss due to SMV would have been approximately AUD 3 million in
1999/2000.
(Discipline
of Microbiology and Immunology, James Cook University, Townsville 4811,
Australia, e-mail: leigh.owens@jcu.edu.au)