The Effects of Microsporidian (Thelohania) Infection on the Growth and Histopathological Changes in Pond-reared Pacific White Shrimp (Litopenaeus vannamei)

Abstract

The effects of microsporidian (Thelohania) infection on the growth and histopathological changes in intensive pond-reared Pacific white shrimp (Litopenaeus vannamei) were studied. Postlarvae 10 (PL10) were stocked at 125 PL/m² in three earthen ponds of approximately 5 rai (8,000 m²) in an area with a salinity of 30-35 ppt. Shrimp were fed with commercial pelleted feed throughout the 120 days of the culture period. Shrimp were first observed to be infected with microsporidian parasites between 20-25 days after stocking. The highest prevalence of infection between 25-28% was found at day 60 in all growout ponds. Subsequently, the prevalence of infection decreased until the shrimp were harvested at day 120 when only 3-5% of shrimp remained diseased from the three rearing ponds. Shrimp infected in both hepatopancreas and abdominal muscle had the lowest weight, which was significantly different (P<0.05) from shrimp infected in only abdominal muscle and the uninfected group from first sampling at day 45 throughout the 120 days of the culture period. Histopathological changes in diseased shrimp from the hepatopancreas-and-muscle-infected group revealed that white masses of microsporidian parasites had partially infested the hepatopancreas and other organs, including the stomach, lymphoid organ and abdominal striated muscle, while in the muscle-infected group only the striated muscles were partially infested by microsporidians. These results clearly indicated that the severity of microsporidian infection negatively affected the growth and survival of white shrimp.