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  • Accepted Manuscript

    Effect of dietary β-glucan on growth, survival and regulation of immune processes in rainbow trout (Oncorhynchus mykiss) infected by Aeromonas salmonicida

    Liqin Ji, Guoxiang Sun, Jun Li, Yi Wang, Yishuai Du, Xian Li, Ying Liu

    PII: S1050-4648(17)30134-1

    DOI: 10.1016/j.fsi.2017.03.015

    Reference: YFSIM 4484

    To appear in: Fish and Shellfish Immunology

    Received Date: 17 December 2016

    Revised Date: 3 March 2017

    Accepted Date: 4 March 2017

    Please cite this article as: Ji L, Sun G, Li J, Wang Y, Du Y, Li X, Liu Y, Effect of dietary β-glucan on growth, survival and regulation of immune processes in rainbow trout (Oncorhynchus mykiss) infected by Aeromonas salmonicida, Fish and Shellfish Immunology (2017), doi: 10.1016/j.fsi.2017.03.015.

    This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

    http://dx.doi.org/10.1016/j.fsi.2017.03.015

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    Effect of dietary β-glucan on growth, survival and regulation of 1

    immune processes in rainbow trout (Oncorhynchus mykiss) infected 2

    by Aeromonas salmonicida 3

    Liqin Jia, b, Guoxiang Suna, Jun Lic, Yi Wangd, Yishuai Dua, Xian Lia, Ying Liud, * 4

    a Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China 5

    b University of Chinese Academy of Sciences, Beijing, 100039, China 6

    c School of Biological Sciences, Lake Superior State University, Sault Ste. Marie, MI, 49783 7 d School of Marine Science and Environment Engineering, Dalian Ocean University, Dalian, 116023, China 8

    ABSTRACT 9

    The present study evaluated the effects of dietary β-glucan (0, 0.05%, 0.1%, and 0.2%) on 10

    growth performance after 42 days of feeding. Thereafter, rainbow trout (Oncorhynchus 11

    mykiss) were infected with Aeromonas salmonicida, and survival rates as well as the 12

    regulating processes of stress- and immune-related factors were analyzed. In general, 13

    higher dietary β-glucan levels obviously improved specific growth rate (SGR), weight gain 14

    (WG) and feed efficiency (FE) (P ≤ 0.05). Survival rates in β-glucan groups increased 15

    significantly compared with the control group after A. salmonicida infection (P ≤ 0.05). 16

    Serum total superoxide dimutase (T-SOD), peroxidase (POD) as well as catalase (CAT) 17

    activities, and their mRNA expressions in the head kidney of fish in the β-glucan groups 18

    generally increased to higher levels after infection, and more quickly, compared with in the 19

    control group. Serum lysozyme (LSZ) and its expression in the head kidney in β-glucan 20

    groups reached a higher peak earlier than in the control group. 21

    22

    *Corresponding author. Tel.: +86-411-84762010; Fax. : +86-411-84763520 23

    E-mail address: yingliu@dlou.edu.cn (Y. Liu) 24

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    Serum glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) 25

    levels in the β-glucan groups were significantly lower than in the control group (P ≤ 0.05). 26

    The peak of heat shock protein 70 (HSP70) expression in the 0.2% β-glucan group was 27

    higher and occurred earlier than in other groups (P ≤ 0.05). These results confirm that 0.1% 28

    and 0.2% dietary β-glucan are beneficial for promoting growth in rainbow trout and 29

    enhancing resistance against A. salmonicida. Furthermore, β-glucan could play an 30

    important role in regulating stress- and immune-related factors in rainbow trout to more 31

    quickly fight against bacterial infection. 32

    Keywords: β-glucan; Oncorhynchus mykiss; growth; survival; immune-related factors; 33

    Aeromonas salmonicida 34

    1. Introduction 35

    Rainbow trout (Oncorhynchus mykiss) is one of the most widely cultured fish 36

    species worldwide for its fast growth and adaptation to low temperature [1]. Despite 37

    the large market demand, natural resources are limited. These factors have led to the 38

    intensification of aquaculture production systems. Intensive farming, along with 39

    overcrowding and poor water quality, is likely to alter fish physiological status and 40

    therefore increase the susceptibility of pathogen infection [2]. In the last few years, 41

    abuse of antibiotics to prevent the uncontrolled spread of pathogens has resulted in 42

    the emergence of several resistant pathogens in aquaculture. Therefore, it is urgent 43

    to find suitable ways to control disease outbreaks [3]. Immunostimulants are the 44

    current primary approach for enhancing resistance against pathogens in aquaculture. 45

    Although numerous substances have been investigated as immunostimulants, only a 46

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    few of these are appropriate for use in aquaculture [4, 5]. 47

    In recent years, the effective immunomodulatory properties of β-1,3/1,6-glucan 48

    derived from yeast have been extensively proved, not only in mammals but also in 49

    fish [6, 7]. β-glucan naturally form polysaccharides with glucose linked by 50

    β-glycosidic bonds [8] and can stimulate macrophages to actively fight against fish 51

    pathogens [9]. They can also enhance the activity of non-specific immune factors 52

    such as lysozyme and the complement system [10, 11]. Altering immune 53

    cytokine-like gene expression, such as tumor necrosis factor-ɑ (TNF-ɑ) and 54

    interleukin-1β (IL-1β), is a primary channel through which β-glucan improves 55

    innate immunity in various fish [12-14]. 56

    Immune efficacy can vary according to several factors such as the dietary dose of 57

    glucan, feeding regime, and glucan type [15]. Although the immunostimulatory 58

    effects of various derivations of β-glucan have been studied against a diverse range 59

    of pathogens, such as Yersinia ruckeri [16], A. hydrophila [17], and bacterial 60

    lipopolysaccharides [18], few studies have investigated its disease resistance against 61

    A. salmonicida. 62

    Therefore, the aim of the present study was to evaluate the effects of dietary 63

    β-glucan derived from yeast cells on growth promotion, disease resistance and 64

    immune response to A. salmonicida in rainbow trout. Furthermore, the manner in 65

    which β-glucan regulates the continuous process of immunity after A. salmonicida 66

    infection was investigated. 67

    2. Materials and Methods 68

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    2.1. Fish husbandry and experimental facilities 69

    This trial was conducted at Shandong Oriental Ocean Sci-Tech Co., Ltd 70

    (Shandong, China). The average initial body weight of rainbow trout was 293.0 ± 71

    18.3 g. At the farming trial, 1200 farmed individuals were randomly placed into a 72

    100-m3 tank containing 80-m3 seawater (average parameters: water flow 7 L/min, 73

    water temperature 12 ℃, oxygen saturation 7.2 mg/L, pH 7.8, and salinity 30‰). 74

    Fish were fed with commercial dry pellets without β-glucan inclusion (Beijing 75

    HanYe Science & Technology Co., Ltd., Beijing, China) prior to the start of the trial. 76

    They were fed 2% of their body weight every day. The feed was divided into five 77

    portions and distributed automatically per day using automatic feeders 78

    (Hangzhou Ecological Environmental Engineering Co., Ltd). 79

    2.2. Experimental diets 80

    β-1, 3-glucan produced by Saccharomyces cerevisiae was purchased from 81

    Angel Yeast Co., Ltd (Hubei, China). The basal diet (commercial diet) was used as 82

    the control diet. For the experimental diets, the basal diet was supplemented with 83

    different levels of β-1, 3-glucan (0.05%, 0.1% and 0.2%). The formulation of the 84

    basal diet is listed in Table 1. 85

    Table 1 86

    Composition of the experimental basal diet. 87

    Ingredients Percentage (%)

    Fish meala 42.8

    Soybean meala 21.2

    DL-methionineb 2.65

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    Fish oilc 15.7

    Wheat flourd 10.8

    Wheat starchd 2.5

    ɑ-Cellulosee 3.5

    Vitamin and mineralf

    0.85

    Proximate composition

    Crude protein 42.18

    Crude lipid

    Ash

    11.23

    11.51

    a Fish meal: crude protein 75.3% dry matter, crude lipid 2.5% dry matter; soybean meal: 51.7% crude 88

    protein dry matter, 2.0% crude lipid of dry matter. Both meals were from Qingdao Fusen Co., Ltd., 89

    Qingdao, China. 90

    b DL-methionine: Guangzhou Shuomu biological technology Co., Ltd., Guangzhou, China. 91

    c Fish oil: Qingdao Fusen Co., Ltd., Qingd