Shrimp diseases - Dystrophy of muscle & hepatopancreas (Loose Shell Syndrome)

Loose shell syndrome (LSS) of farmed shrimp has been reported from many parts of the world and is recognized as a major disease problem causing significant economic loss to the shrimp aquaculture sector.

Unlike the rapid mortalities associated with viral pathogens such as White Spot Syndrome Virus and yellow head virus, progression of LSS is gradual, leading to low-level progressive mortalities.

The signs of LSS include a flaccid spongy abdomen due to muscular dystrophy, space between the exoskeleton and muscle, and a shrunken hepatopancreas.

The feed conversion efficiency is reduced and shrimp have poor meat quality, caused by impairment of the hepatopancreatic functions such as digestion and absorption as evidenced by the atrophy of the hepatopancreas.

Histopathological investigations on LSS-affected shrimp showed shrinkage of extensor and flexor muscles with occasional hemocytic infiltration.

The hepatopancreas showed inflammation of hepatopancreatic tubules with enlargement of intertubular spaces, hemocytic infiltration and low levels of lipid reserves in the R cells.

In advanced stages of LSS, many tubules were in highly necrotic condition with a sloughed epithelium, reflecting the dysfunction of the digestive gland.