Except for exuvia entrapment disease, information on nutritional deficiency diseases in freshwater prawns is sparse. The symptoms of nutritional deficiency are difficult to recognize and most do not manifest externally. The effects are however realized by poor survival and growth.
In the absence of dietary essential fatty acids (EFA) the size of the midgut gland is significantly reduced. Low levels of HUFAs results in poor growth and survival. Heinen (1984) also noticed considerable mortality in the absence of dietary vitamin C and pyridoxine.
The exact aetiology of exuvia entrapment disease (EED)/ Moult death syndrome (MDS)/ metamorphosis moult mortality syndrome is currently not known. The affected prawns find it difficult to cast off the old exoskeleton (exuvia). It is prevalent in late larval rearing at the metamorphic moult to the post larval stage, often resulting in mass mortality. Harpaz and Schmalbach (1986) reported a reduced incidence of moult death syndrome when prawns are fed with diets containing higher levels of plant material.
Recently, Ravi Kumar et al. (2004) documented a new disease, viz. appendage deformity syndrome (ADS), in M. rosenbergii that results in high mortality. Their findings suggest that carotenoid deficiency may the cause. Infected prawns show unusual gross signs like appendage deformity, broken or bent rostrums, cut antennae, wrinkled carapace (Figures 5 and 6), white color ovaries and higher rates of mortality. The gross signs of ADS are more prevalent in females than males. ADS is a chronic post maturity disease that manifests itself after 4 to 6 months of culture.
