Research into deficiency diseases of shrimp is limited as compared to similar research on fish (e.g. FAO, 1992).
Vitamin deficiency
Vitamin deficient diets can cause poor appetite, slower growth, increased mortalities and poor feed conversion efficiencies. Vitamin deficiencies can cause histological changes in the digestive gland cells (Lightner et al., 1977; Chen, Wu and Tang, 1991; Couch and Fournie, 1993; Jintoni, 2002; Rai and Reddy, 2004).
Cramp tail syndrome
Another nutrition-related disease found in P. indicus is cramped-tail syndrome (CTS) (Couch and Fournie, 1993). Cramping occurs during handling and death usually follows. The disease is possibly associated with a mineral imbalance or increased water and air temperatures, e.g. during handling of shrimp in air warmer than the culture water (Liao and Chin, 1980; Jintoni, 2002). An acceptable level of CTS would be 5 percent or less (Clifford and Cook, 2002).
Soft-shell syndrome
Feed quality (rancid or low-quality feeds) may also lead to a condition called soft-shell syndrome. Nutritional deficiency, pesticide contamination and poor pond water and soil condition have all been associated with this condition (Jintoni, 2002). The shell of affected animals is thin and persistently soft for several weeks. Affected shrimp grow slowly and eventually die.
Blue disease or pigment deficiency syndrome (PDS)
Blue disease has been called by a variety of names including pale colouration, blue disease, sky blue shrimp disease and blue shell syndrome (McVey, 1993). Pigment deficiency syndrome (PDS)) is associated with low levels of the carotenoid astaxanthin. The disease is observed in intensive culture systems toward the end of the growout culture period (Jintoni, 2002). It is also associated with bleaching of broodstock ovaries and reduced early larval performance in species such as P. indicus (Regunathan and Wesley, 2006). Treatment is through the provision of a diet with carotenoid sources (Jintoni, 2002). Broodstock performance can be improved by feeding 30 g/kg Spirulina supplemented diet immediately after the appearance of clinical signs (Regunathan and Wesley, 2006). Carotenoid content in commercially available Spirulina ranges from 3.5 to 5.7 g/kg. A diet containing 50 ppm of astaxanthin fed over four weeks should restore normal colouration (Menasveta et al., 1993).
Aflatoxin poisoning, “red disease”
The mould Aspergillus sp. is a common contaminant in prawn feeds and leads to aflatoxin in the food (FAO, 2004b). This causes red disease or red discolouration. Check for old, rancid feeds and feeds stored in hot conditions. Fifty micrograms of aflatoxin per gram of feed causes atrophy and necrosis of the hepatopancreas (Jintoni, 2002). The condition leads to gradual mortalities and up to 98 percent total mortality in three months.
Black spot
Chitinolytic bacteria are associated with diseases of invertebrates (West, 1988). Usually associated with some injury, shrimp occasionally has black eroded spots on their exoskeletons (bacterial shell disease) (Bower, McGladdery and Price, 1994). The frequency increased in winter when moults slowed.
Bacterial infections
NHP-like disease occurs in pond-reared P. indicus. Necrotizing hepatopancreatitis (NHP) is a disease of cultured Penaeus vannamei caused by a Gram-negative intracellular bacterium rickettsia-like organism (Aranguren et al., 2006; NACA, 2007). This can be treated with oxytetracycline included in the feed at 1.5 g/kg (OIE draft), followed by a 25 d withdrawal period before harvesting (Nogueira-Lima, Gesteira and Mafezoli, 2006).
Cotton disease
In South Africa, microporidian (Sindermann, 1974; ASEAN, 1978; Toubiana et al., 2004) infections occurred each year in a percentage of P. indicus in some ponds. Most shrimp would die before reaching a few grams in size, but some would grow to harvest at 20 g (author’s observation).
