Fish Diseases and Management

3.2.7.Establishment of health criteria in reared penaeid shrimp and analysis of immune parameters under stress conditions

Quantitative assays for evaluating immune effectors have been optimised for levels of total and differential haemocyte counts, phenoloxidase activity, respiratory burst, and plasma agglutinating activity together with plasma antibacterial activity and quantification of some plasma proteins, such as the clotting factor, an agglutinin, and $$\alpha$$-2- macroglobulin, using immunoenzymatic assays with specific antibodies. The measured immune parameters were to be first obtained on apparently healthy shrimp in intermoult. Under controlled environmental conditions, the immune responses of shrimp were evaluated.

Haemocyte count and respiratory burst were found to be low when temperature and O₂ decreased in water or when the level of ammonia increased. The effect of salinity showed that when salinity decreases, THC decreases too. The fungicide propiconazole used in agriculture and found as residual contamination in shrimp ponds was shown to have a disturbing effect on the immune response in shrimp injected at different concentrations (1, 10 and 100 ppb), affecting haemogramme, respiratory burst, plasma protein concentrations and antibacterial activity.

Preliminary studies showed a correlation between the level of protein in food and the immune profile in terms of total haemocyte count and level of plasmatic proteins. Immune parameters in P. stylirostris were assessed before the shrimps were experimentally infected with a highly pathogenic bacteria (Vibrio penaeicida). The survivors had significantly higher THC and phenoloxydase activity than dead shrimp suggesting that shrimp with high immune profile are more resistant to vibriosis than those with a low immune profile. It appears that several factors affect the immune response in shrimp. Further studies are required to get a better understanding of ways to increase the immune status of farmed shrimp populations.