The success of penaeid shrimp aquaculture has been limited by endemic and epidemic infectious diseases around the world and shrimp defense mechanisms are a priority for control, prevention, and diagnosis. The lethal dose (LD50) of Escherichia coli lipopolysaccharides was calculated and pathogen injection and dissolved ammonia concentration on immune response were evaluated in southern white shrimp Litopenaeus schmitti. The lethal dose of lipopolysacharides was 3.78 mg kg- 1body weight. Injection caused changes in phenoloxidase activity in plasma and nitric oxide and total haemocyte counts within the first 24 h. High concentration of dissolved ammonia caused a decrease in haemocytes by 66% within the first 72 h, when compared to the control. Hemagglutination in plasma was not affected by injection or high concentrations of dissolved ammonia. The results showed that white shrimp recognized the lipopolysacharides and responded to this microbial elicitor, as indicated by a variety of immunological indicators and that increased dissolved ammonia affected the number of circulating haemocytes. © 2007 Elsevier B.V. All rights reserved.
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