Abstract:
Results of preliminary observations carried out and recorded by some grow out farm managers
indicated that the cultured shrimp stocks predisposed to vibriosis are easily susceptible to white
spot viral disease. Therefore the present study was carried out in May, 2005 when most of the
shrimp grow out ponds at Arachchikattuwa area were affected with white spot disease to see
whether there is any relationship between systemic vibriosis and white spot disease.
A farm with 5 earthen ponds at Arachchikattuwa area was selected and a commercially available
probiotic was used to suppress the Vibrio populations in 3 ponds; other 2 ponds did not receive
the probiotic . Weekly random samples of shrimp were observed from each pond and haemolymph
was inoculated on TCBS agar and cephalothorax of these shrimp were preserved in Davison Afa
for histological preparations. Shrimp in each pond were observed for gross clinical signs of white
spot disease.
Heamolymph samples obtained from the shrimp of the 2 ponds that did not receive the probiotic
treatment gradually increased and reached 480 ± 73 cfu/ml of haemolymph and such shrimp had
multifocal melanized and/ or non-melanized haemocytic nodules with septic centers which is the
principal diagnostic feature of systemic vibriosis. The stocks of shrimp in these 2 ponds exhibited
gross clinical signs of white spot disease within 10-12 days (from the date they had Vibro count of
480±73 cfu/ml of haemolymph) and emergency harvest was carried out. In contrast, haemolymph
of shrimp was free of Vibrio in the ponds that received the probiotic treatment and the shrimp did
not develop systemic vibriosis and farm manager could complete the normal production cycle.
Results of the present study suggest that systemic vibriosis is a predisposing factor for the occurrence
of white spot disease in shrimp, P.monodon in grow out ponds.