Q2. How was the glucan content judged optimal?
After feeding the glucan containing diets, a glucan content of 0.2% was judged optimal based on the highest protection against WSSV during experimental infection.
Q3. How was the post larvae challenged with WSSV?
The post larvae were challenged with white spot syndrome virus (WSSV) by feeding WSSV infected shrimp (F. indicus) tissue (1 g/25 post larvae) on the 22nd day.
Q4. What is the reason for the low survival of shrimp at higher concentrations of glucan?
The low survival of shrimp at higher concentrations of glucan also could be attributed to the continuous overproduction of superoxide anions and free radicals generated from the respiratory burst activity of the phagocytic haemocytes, causing non-specific host injury.
Q5. What is the role of -glucans in the immune system of shrimp?
β-glucans have been used as immunostimulants to enhance the defence potential of fish and shellfish against bacterial or viral infection (Oliver et al., 1986; Sung et al., 1994; Song et al., 1997; Chang et al., 1999, 2000, 2003).
Q6. What is the effect of glucan on the immune system?
Soderhall et al. (2003) reported that injection of β1,3-glucan into the haemocoel of a crustacean resulted in an accelerated maturation of haemocyte precursors in the haematopoie-tic tissue followed by release of new cells into the circulation.
Q7. What is the reason for the glucan effect in a crustacean?
It presumes that higher concentrations of glucan caused excessive degranulation of both granular and semigranular haemocytes resulting in the release of prophenoloxidase and an exhaustion of immune system.
Q8. What is the reason for the decreased immune system?
Host homeostasis seems to be impaired due to high concentrations of glucan, a condition very similar to an acute infection by a pathogen leading to the reduction in circulating haemocytes.
Q9. How many shrimps were challenged with white spot syndrome virus?
On the 41st day, the shrimps were challenged with white spot syndrome virus by feeding WSSV infected prawn tissue at the rate of 1 g/shrimp.
Q10. What is the reason for the low dose of glucan in crustaceans?
The short lived nature of protection, lack of linear dose–effect relationship and lack of immune memory make the regimes of immunostimulant application in crustaceans complicated.
Q11. What is the effect of prophylactic measures on the animals?
such prophylactic measures may result in impaired immunity in animals and in the event of an infection, they may easily succumb to death.
Q12. What is the mechanism to restore the haemocyte number?
In such situations the mechanism to restore the haemocyte number is mobilizing the haemocytes from the reservoirs in haemal crypts or upregulation of cell division in the haematopoietic tissue and proliferation within the haemolymph (Ghiretti-Magaldi et al., 1977; Hose et al., 1992).
Q13. What is the purpose of this study?
This study emphasizes the fact that the dose and frequency of application of immunostimulants in shrimp aquaculture should be standardised and validated before commercialisation to achieve optimum stimulation of the immune system and to avoid immune fatigue due to overdose.
Q14. How was the haemolymph removed from the rostral sinus?
Haemolymph was withdrawn aseptically from the rostral sinus using specially designed sterile capillary tubes having a diameter of 0.5 mm, pre-rinsed with anticoagulant (0.01 M Tris HCl, 0.25 M sucrose, 0.1 M trisodium citrate, prepared in double distilledwater, autoclaved and adjusted to pH 7.6; Song and Hsieh, 1994) and transferred to a sterile microcentrifuge tube containing cooled anticoagulant.
Q15. How many days were the other groups fed the glucan diet?
The other groups were maintained on the 0.2% glucan diets at definite feeding intervals, i.e. daily (G1); once every seven days (G7) and once every ten days (G10).
Q16. How long did the shrimp survive in the laboratory?
The shrimp, after seven days quarantine, were randomly divided into four groups of 60 shrimp per aquarium of 500 L capacity and acclimatized to the laboratory conditions for one week.
Q17. How many days did the shrimps survive a WSSV challenge?
The shrimps fed 0.2% glucan at a feeding frequency of once every seven days showed significantly higher immune response compared to the control and other treatment groups (Pb0.05).
Q18. What was the spectrophotometric activity of the haemocytes?
Respiratory burst activity of haemocytes was measured spectrophotometrically (Song and Hsieh, 1994) using nitroblue tetrazolium (NBT) as the substrate.
Q19. How many days were the post larvae fed the glucan diet?
The post larvae were divided into six groups and each group was fed the 0.2% glucan diet at different frequencies viz., daily (G1), once every two days (G2), once every five days (G5), once every seven days (G7) and once every ten days (G10).
Q20. What is the effect of glucan incorporated diet on F. indicus?
In the present study, even though the glucan incorporated diet did not provide total protection for F. indicus against WSSV, the partial protection would help the aquaculture industry to plan for a prior harvest and to save the crop from mass mortality.
Q21. What is the significance of the glucan diet in shrimp farming?
These observations emphasize the importance of dose/frequency of application of immunostimulants in shrimp farming for imparting protection against pathogens.