Occurrence of microsporidian in white faeces syndrome (WFS)-diseased Litopenaeus vannamei of intensive grow-out ponds of India

The present study aimed to investigate the pathogenesis of white faeces syndrome (WFS) in Litopenaeus vannamei and its impact on grow-out production. Microsporidian infection clinically causes white gut, loose shell, opaque muscle, jelly-like accumulation in the hepatopancreas and in severe cases the white faeces strands floating on the surface of the ponds. The daily growth rate (DGR) of shrimp in the infected pond (ranged between 0.13 and 0.34 g) was lower than that in the normal pond. The minimum disease prevalence of 4% and a maximum prevalence of 26% were recorded. In the histological study, the hepatopancreas and gut were the most affected organs of shrimps. Hepatopancreatic tubules were sloughing and degenerated where some basophilic inclusions were observed. In the infected midgut, the columnar cells, basement membrane and muscles were severely degraded. The oval-shaped spores of the microsporidian were found to be observed under the examination of a scanning electron microscope, which is confirmed by the transmission electron microscopy. The total length of the matured spores ranged between 1000 and 1300 nm (1130 +/- 80 nm). The different maturation phases of microsporidian in infected hepatopancreas were found to be observed under a TEM. The mature spore consisted of exosphore, the outer surface covered with protein layer, and endosphore, the inner layer made up of chitin followed by the plasma membrane.