Pythium insidiosum as a new opportunistic fungal pathogen for Pacific white shrimp, Litopenaeus vannamei

The moribund shrimps were exhibiting yellow discoloration of the cephalothorax, blackening of gills and ulcers in the uropod and telson region. PCR for OIE listed viral pathogens ruled out known viral infections. No bacteria was present in haemolymph however, low level of Vibrios i.e. Vibrio harveyi, V. parahaemolyticus and V. alginolyticus was found both in the water collected from the broodstock tanks and affected tissue region. Histopathological examination of affected tissues revealed presence of highly invasive fungal hyphae both by routine and specific fungal stain. PCR amplification of the ITS region (approximately 900 bp) and sequencing confirmed presence of Pythium insidiosum. Phylogenetic analysis of this isolate placed it among the environmental isolates.