Effects of oligochitosan on the growth, immune responses and gut microbes of tilapia (Oreochromis niloticus)

doi:10.1016/j.fsi.2020.07.049

Fish & Shellfish Immunology

Volume 106, November 2020, Pages 563-573

https://doi.org/10.1016/j.fsi.2020.07.049 Get rights and content

Highlights

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Dietary oligochitosan can improve the growth, immune response and enhance resistance to A. hydrophila infection.
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The discriminatory dominant genera showed higher positive interaction in tilapia when feeding oligochitosan.
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Beta-diversity revealed hindgut would be a relatively sensible ecosystem target.
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Habitat filtering by gut compartment is the major driver in shaping gut bacterial assembly in tilapia.

Abstract

The immunomodulatory effects of oligochitosan have been demonstrated in several fish. However, the underlying mechanisms are not well characterized. The profound interplay between gut microbes and aquaculture has received much scientific attention but understanding the alternations of microbes populating in gut of tilapia (Oreochromis niloticus) fed with oligochitosan remains enigmatic. In this study, the effects of oligochitosan on the growth, immune responses and gut microbes of tilapia were investigated. The feeding trial was conducted in triplicates with the control diet supplemented with oligochitosan at different concentrations (0, 100, 200, 400 or 800 mg/kg). Following a six-week feeding trial, body weights of the fish supplemented with 200 mg/kg and 400 mg/kg oligochitosan were significantly higher than that of the control group. To address the immune responses stimulated by oligochitosan, by the quantitative real time PCR (qRT-PCR), the mRNA expression levels of CSF, IL-1β, IgM, TLR2 and TLR3 genes from head kidney were all significantly up-regulated in the 400 mg/kg group compared to the control. To characterize the gut microbes, bacterial samples were collected from the foregut, midgut, and hindgut, respectively and were subjected to high-throughput sequencing of 16S rDNA. The results showed that significantly lower abundance of Fusobacterium was detected in the hindgut of 400 mg/kg group compared to the control. Additionally, beta-diversity revealed that both gut habitat and oligochitosan had effects on the gut bacterial assembly. To further elucidate the mechanism underlying the effects of oligochitosan on bacterial assembly, the results showed that difference dosages of dietary oligochitosan could alter the specific metabolic pathways and functions of the discriminatory bacterial taxa, resulting in the different bacterial assemblies. To test the antibacterial ability of tilapia fed with oligochitosan, when the tilapias were challenged with Aeromonas hydrophila, the mortality of groups fed with dietary oligochitosan was significantly lower than that of the control. Taken together, appropriate dietary oligochitosan could improve growth, immune responses and alter the bacterial flora in the intestine of tilapia, so as to play a role in fighting against the bacterial infection.

Introduction

Aquaculture has become one of the fastest growing industries for food nutrition, it employs millions of people, and improved technology and management practices are required in order to meet the increasing demand for human consumption. Due to its rapid growth and market value, tilapia is one of the most cultured commercial fish species farmed in over 135 countries [1]. According to recent data from the Food and Agriculture Organization (FAO, 2018), global production of tilapia was approximately 5.73 million tons, which accounted for 10% of global freshwater aquaculture production [2]. The deterioration of aquaculture environment and numerous bacterial diseases outbreaks have seriously impacted on tilapia production, which jeopardizes the tilapia aquaculture industry. The increasing global ban on antibiotic usage has led to the search for alternative natural feed supplements, so as to improve the growth and immunity of tilapia.

Chitosan, a polysaccharide of β-1,4-2-deoxy-2-amino-d-glucopyranose, is the second most abundant natural biopolymer [3]. Due to its low-toxicity, biocompatibility, biodegradability and low-cost, chitosan has received a large amount of attention [4,5]. Many studies have proven that chitosan has many physiological functions, such as having effects on the growth performance, immunity and antimicrobial ability on fish [5]. There have been reported that supplementation of dietary chitosan have affected various aquatic animals, including rainbow trout (Oncorhynchus mykiss) [6], sea bass (Dicentrarchus labrax) [7], common carp (Cyprinus carpio) [8], Nile tilapia (O. niloticus) [9], kelp grouper (Epinephelus bruneus) [10], white-leg shrimp (Litopenaeus vannamei) [11] and black tiger shrimp (Penaeus monodon) [12]. Oligochitosans can be obtained by either chemical or enzymatic hydrolysis of chitosan, resulting in an oligomer mixture with 3–10 saccharide residues. They are soluble in neutral aqueous solutions with low molecular weight and low viscosity which can be effectively absorbed by the intestine [13]. Studies have shown that mannose receptor is required for the absorption of oligochitosans which mediate a variety of immune activities through the activation of macrophage cells [[14], [15], [16], [17], [18], [19], [20], [21], [22]].

Gut microbial communities play major roles in the defense mechanism of the host, which can be easily affected by nutrient metabolism, immune function and disease resistance [[23], [24], [25], [26], [27]]. Pathogen infections are the main issues in intensive fish culture, in which many stressful situations affect the immune responses of the cultured fish [[28], [29], [30], [31], [32], [33], [34]]. In previous studies, dietary chitosans or chitooligosaccharides were reported to enhance growth, immune-modulatory and antimicrobial effects in tilapia [9,30,35]. However, the effects of oligochitosan on gut bacterial communities in tilapia have not yet been studied. Therefore, the current study was designed to scrutinize the dietary supplementation of oligochitosan at various concentrations on growth performance, innate immunity, gut bacterial community and disease resistance. The results will pave a new way for the development of dietary oligochitosan for the fish feed.

Section snippets

Preparation of experimental diets and feeding

Juvenile tilapias (10 ± 5 g) were obtained from a fish farm located at Guangzhou city, Guangdong province, China. The fish were acclimatized in tanks with filtered and aerated fresh water at a temperature of 29 ± 1 °C for two weeks before the experiments. Oligochitosan mixture with 3–10 saccharide residues was purchased from Huizhou Long Dragon Biotechnology Co. Ltd, China. Fish were randomly divided into five groups (120 fish in one group) with triplicates. Fish were fed with diets which were

Oligochitosan enhanced growth performance of tilapia

To investigate the effect of oligochitosan on tilapia growth, we first assessed the body weight of the animals at the end of the 6-week feeding trial with different concentrations of oligochitosan. As shown in Fig. 1A, the body weights of the fish supplemented with 200 mg/kg or 400 mg/kg oligochitosan were significantly higher than the control group (p < 0.05), however, there were no significant differences in the 100 mg/kg and 800 mg/kg groups (p > 0.05). Comparing the average values of

Discussion

A number of feed additives, including oligochitosan, have been widely employed in the aquaculture industry, many studies have focused on the metabolic effect and other physiological functions [5]. However, whether oligochitosan will affect the diversity and composition of intestinal microbes and as well as the immune response of intestinal in tilapia fish are not yet characterized. In the present study on tilapia that fed with different concentrations of oligochitosan over 6 weeks was performed

CRediT authorship contribution statement

Fei Shi: Formal analysis, Writing - original draft. Xiaolong Qiu: Formal analysis. Lingju Nie: Writing - original draft. Luoying Hu: Writing - original draft. Sarath Babu V: Writing - original draft. Qiang Lin: Writing - original draft. Yulei Zhang: Writing - original draft. Liehuan Chen: Writing - original draft. Jun Li: Writing - original draft. Li Lin: Writing - original draft. Zhendong Qin: Writing - original draft.

Acknowledgments

This research was jointly supported by the National Natural Science Foundation of China (31902409, 31872606, 31861143051, 31872425, 31572657, U1701233); Guangdong marine economy promotion projects (MEPP) Fund (GDOE2019A20); Guangdong South China Sea Key Laboratory of Aquaculture for Aquatic Economic Animals, Guangdong Ocean University (KFKT2019YB04); Key Laboratory of Fishery Drug Development, Ministry of Agriculture and Rural Affairs (201805). Foundation of Guangdong Provincial Marine and

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¹: These two authors contributed equally.

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Full length articleEffects of oligochitosan on the growth, immune responses and gut microbes of tilapia (Oreochromis niloticus)

Highlights

Abstract

Introduction

Section snippets

Preparation of experimental diets and feeding

Oligochitosan enhanced growth performance of tilapia

Discussion

CRediT authorship contribution statement

Acknowledgments

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Full length article
Effects of oligochitosan on the growth, immune responses and gut microbes of tilapia (Oreochromis niloticus)

The growth, innate immunity and protection against H₂O₂-induced oxidative damage of a chitosan-coated diet in the olive flounder (Paralichthys olivaceus)