The prebiotic inulin increases the phenoloxidase activity and reduces the prevalence of WSSV in whiteleg shrimp (Litopenaeus vannamei) cultured under laboratory conditions
Highlights
► This study evaluated the effect of prebiotics in Litopenaeus vannamei. ► Inulin increases phenoloxidase activity in shrimp and had a beneficial effect against WSSV. ► Inulin is a good candidate to be used as feed additive in shrimp culture.
Introduction
Shrimp aquaculture is an important worldwide industry. However, since several years ago shrimp farming has been threatened by diseases that have affected its production performance due to mismanagement and the lack of biosecurity protocols. Viral diseases, such as the white spot syndrome virus (WSSV), can cause severe mortalities in cultured shrimps (Chou et al., 1995, Leu et al., 2009, Lo et al., 2003). In Mexico, the states of Sonora and Sinaloa, located in the northwest of the country, are the most important whiteleg shrimp producers; however, in the last years important losses have occurred due to WSSV (CONAPESCA, 2010, Peinado-Guevara and López-Meyer, 2006).
Traditionally, to successfully restrict pathogen infection, farmers apply basic practices of good management and use chemotherapy (antibiotics) (Subasinghe and Barg, 1998). Shrimp cannot be vaccinated, thus, antibiotics are currently used; however, these chemicals have been gradually prohibited due to the potential development of antibiotic-resistant bacteria, presence of antibiotic residues in seafood, environmental impact, and suppression of the aquatic animals' immune system (Li et al., 2007, Zhou et al., 2007). An alternative to the use of antibiotics as growth promoters is to feed natural origin additives such as probiotics, prebiotics, immunostimulants, and medicinal plants (Partida-Arangure, unpublished data).
Immunostimulants are aimed at enhancing the non-specific defense mechanisms in animals. A number of different biological and synthetic compounds have been found to enhance the non-specific defense system in animals, including shrimp (Song and Sung, 1990, Sung et al., 1991).
Prebiotics are non digestible polysaccharides added to feed that beneficially affect the host by selectively stimulating the growth of and/or activating the metabolism of one or a limited number of health-promoting bacteria in the intestinal tract, thus improving the host's intestinal balance (Gibson and Roberfroid, 1995, Manning and Gibson, 2004). The prebiotics include fructooligosaccharides (FOS), transgalactooligosaccharides (TOS), mannanoligosaccharides (MOS), lactose, and inulin (Teitelbaum and Walker, 2002, Vulevic et al., 2004). Inulin and its derivates (oligofructose, fructooligosaccharides) are generally known as fructans and are basically constituted by linear chains of fructose (Madrigal and Sangronis, 2007). Several inulin types occur in nature and they differ in their degree of polymerization and molecular weight, depending on the source, the harvest time, and processing conditions (Vijn and Smeekens, 1999). Diets supplemented with FOS have been shown to improve the immunity and growth rate of aquatic animals such as soft-shell turtle (Ji et al., 2004), turbot larvae (Mahious et al., 2006), and white shrimp (Li et al., 2007, Zhou et al., 2007).
Shrimp possess an innate immune system. The hemocytes and plasmatic molecules are key elements against pathogens. Hemocytes play a central role in the immune response of shrimp, which rely mainly on phagocytosis, melanization through the activation of the proPO cascade, encapsulation, cytotoxicity, and hemolymph clotting mechanism (Cerenius et al., 2008, Sritunyalucksana et al., 1999). Humoral defense factors, such as agglutinins, clotting proteins, lisosomal hydrolytic enzymes (proteases, glycosidases, lipases, phosphatases), and antimicrobial peptides (penaedins) are released upon lysis of hemocytes, which is induced by microbial surface antigens, such as peptidoglycans, lipopolysaccharides (LPS), and b-1,3-glucans (Chisholm and Smith, 1995, Destoumieux et al., 2000, Muta and Iwanaga, 1996, Söderhäll et al., 1994).
The aim of this study was to evaluate the effect of the prebiotic inulin on growth, survival, immune system, and prevalence of WSSV in Litopenaeus vannamei cultured under laboratory conditions.
Section snippets
Animals
Two batches of 150 and 120 apparently healthy shrimp, based on visible features, were collected from a commercial farm (Acuícola Cuate Machado, Guasave, Sinaloa, Mexico) and immediately transported to the lab facilities of CIIDIR Sinaloa in a plastic container (250 L) provided with sea water and aeration. The collected shrimp had no signs of WSSV, IHHNV, and/or bacterial infections. However, farmers specified that shrimp had WSSV.
Shrimp acclimation to culture conditions
The healthy shrimp selection was done based on visible features.
Effect of inulin on survival, WSSV prevalence, SGR, and LAB (bioassay 1)
Shrimp survival (Table 1) was high (80 ± 10 to 96 ± 5.7%) in all treatments and no significant differences were found among the treatments (p > 0.05). WSSV prevalence (Table 1) in treatment I was 58%; in treatment II, 41.7%; in treatment III, 16.6%; in treatment IV, 16%; in treatment V, 41.7%. Results showed that inulin reduces WSSV prevalence, especially at concentrations of 2.5 and 5 g inulin kg feed− 1. Results (Table 1) showed values of SGR from 2.9 ± 0.2 to 3.0 ± 0.0 (% day− 1). Experimental shrimp were
Discussion
Control strategies against shrimp diseases are necessary (Li-Shi et al., 2007). In accordance with this point of view, the present study was carried out to investigate whether oral administration of prebiotics is capable of protecting L. vannamei against WSSV. Prebiotics have been recognized for increasing growth rate, improve immune response, as well as change the community of gastrointestinal microbiota in cultured animals (Li et al., 2007, Yousefian and Sheikholeslami, 2009, Zhou et al., 2007
Conclusion
Inulin increases the PO activity on L. vannamei. This study is the first report to show that a prebiotic, inulin, reduces the WSSV prevalence in shrimp with low viral load.
Acknowledgments
Authors are grateful to Consejo Estatal de Ciencia y Tecnología del Estado de Sinaloa (CECyT-Sinaloa) and Secretaría de Investigación y Posgrado del Instituto Politécnico Nacional (SIP-IPN) for financial support. Judith Cristina Almaraz Salas acknowledges CONACYT Mexico and SIP-IPN for the M.S. grants.
References (40)
- et al.
Characterization of a prophenoloxidase from hemocytes of the shrimp Litopenaeus vannamei that is down-regulated by white spot syndrome virus
Fish & Shellfish Immunology
(2008) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding
Analytical Biochemistry
(1976)- et al.
The proPO-system: pros and cons for its role in invertebrate immunity
Trends in Immunology
(2008) - et al.
Comparison of antibacterial activity in the hemocytes of different crustacean species
Comparative Biochemistry and Physiology
(1995) - et al.
Dietary modulation of the human colonic microbiota; introducing the concept of prebiotics
Journal of Nutrition
(1995) - et al.
Activation of the prophenoloxidase system of the brown shrimp (Penaeus californiensis Holmes)
Comparative Biochemistry and Physiology
(1996) - et al.
Dietary supplementation of short-chain fructooligosaccharides influences gastrointestinal microbiota composition and immunity characteristics of Pacific white shrimp, Litopenaeus vannamei, cultured in a recirculating system
Journal of Nutrition
(2007) - et al.
Prebiotics
Best Practice & Research. Clinical Gastroenterology
(2004) - et al.
The role of hemolymph coagulation in innate immunity
Current Opinion in Immunology
(1996) - et al.
Detailed monitoring of white spot syndrome virus (WSSV) in shrimp commercial ponds in Sinaloa, Mexico, by nested PCR
Aquaculture
(2006)