A new bacterial white spot syndrome (BWSS) in cultured tiger shrimp Penaeus monodon and its comparison with white spot syndrome (WSS) caused by virus

This paper describes a new bacterial white spot syndrome (BWSS) in cultured tiger shrimp Penaeus monodon. The affected shrimp showed white spots simil ar to those caused by white spot syndrome virus (WSSV), but the shrimp rema ined active and grew normally without significant mortalities. The study re vealed no evidence of WSSV infection using electron microscopy, histopathol ogy and nested polymerase chain reaction. Electron microscopy indicated bac teria associated with white spot formation, and with degeneration and disco loration of the cuticle as a result of erosion of the epicuticle and underl ying cuticular layers. Grossly the white spots in BWSS and WSS look similar but showed different profiles under wet mount microscopy. The bacterial wh ite spots were lichen-like, having perforated centers unlike the melanized dots in WSSV-induced white spots. Bacteriological examination showed that t he dominant isolate in the lesions was Bacillus subtilis. The occurrence of BWSS may be associated with the regular use of probiotics containing B. su btilis in shrimp ponds. The externally induced white spot lesions were loca lized at the integumental tissues, i.e., cuticle and epidermis, and connect ive tissues. Damage to the deeper tissues was limited. The BWS lesions are non-fatal in the absence of other complications and are usually shed throug h molting.