Elsevier

Aquaculture

Volumes 362–363, 28 September 2012, Pages 28-32
Aquaculture

The prebiotic inulin increases the phenoloxidase activity and reduces the prevalence of WSSV in whiteleg shrimp (Litopenaeus vannamei) cultured under laboratory conditions

https://doi.org/10.1016/j.aquaculture.2012.07.022Get rights and content

Abstract

The effect of inulin on growth performance, survival, lactic acid bacteria (LAB) in the gut, WSSV prevalence, and immune response of Litopenaeus vannamei was evaluated under laboratory conditions. Inulin was sprayed onto feed at 0, 1.25, 2.5, 5.0, and 10 g kg feed 1. Two bioassays, performed with treatments in triplicate, were conducted for 62 and 73 days, respectively. Feed supplemented with inulin did not improve growth, survival, and LAB in shrimp. However, inulin decreased the prevalence of WSSV in treated shrimp. The prebiotic significantly increased the phenoloxidase activity, but hemocyte number was not affected. Inulin increases the phenoloxidase activity in L. vannamei and, at concentrations of 2.5 and 5.0 g kg feed 1, is a good feed additive against WSSV in shrimp with low viral load.

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.

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