Dose/frequency: A critical factor in the administration of glucan as immunostimulant to Indian white shrimp Fenneropenaeus indicus
Introduction
Outbreaks of diseases are being increasingly recognized as a significant constraint in aquaculture production. Among shrimp pathogens, white spot syndrome virus (WSSV) causes high mortality in cultured shrimp species viz. Penaeus monodon, Fenneropenaeus indicus, Marsupenaeus japonicus and Penaeus semisulcatus (Lightner, 1996, Lo et al., 1997). Polysaccharides from a variety of sources enhance the immune system of animals and pharmacologically they are known as biological response modifiers (BRMs) (Leung et al., 2006). The most active of these compounds is (1–3)-β-d-glucan (Bhon and Be Miller, 1995), a natural polymer isolated from the cell wall of yeast and mold. 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, Chang et al., 2000, Chang et al., 2003). Currently many commercial immunostimulants are available in the shrimp aquaculture industry and are extensively used by shrimp farmers. However, scientific data in support of their function and dose/frequency of application are lacking. Information regarding the dose is essential as overdose leads to immunosuppression rendering less protection and animals succumb to infection. In the present study, the immunostimulatory effect of an alkali insoluble cell wall glucan preparation from a marine yeast isolate Candida sake S165 (Sajeevan et al., 2006) was tested in F. indicus and the dose/frequency was optimised.
Section snippets
Glucan extraction
C. sake S165, isolated from the coastal waters off Cochin and maintained in the Microbiology Laboratory of the Department of Marine Biology, Microbiology and Biochemistry, School of Marine Sciences was used for the study. A pure lawn culture of C. sake was prepared using Malt Extract Agar (malt extract, 20 g; mycological peptone, 5 g; agar, 20 g; 20‰ seawater 1 L, pH 6) and the biomass was harvested at exponential phase into sterile seawater (20‰). The harvested cells were then separated by
Results and discussion
The alkali extraction of particulate glucan from the cell wall of the marine yeast C. sake S165 was found to give a yield of 12.3% of the dry weight of the yeast biomass. 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. Post challenge survival against WSSV on the 7th day with the 0.2% glucan (54.17 ± 3.62%) feed was found to be significantly different from the other treated groups
Acknowledgement
The authors are grateful to the Department of Ocean Development (DOD), Govt. of India for a research grant (F.No.DOD/II-MRDF/4/3/UNI/97-(P-6)) with which the work was carried out. We thank R. Bernard (University of Kentucky) and R. Rajesh (University of Michigan) for critical evaluation of the manuscript. The first author gratefully acknowledges DOD for the fellowship rendered.
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