Aquaculture Nutrition E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Manipulation of the microbial gut content of farmed fishes and crustaceans can have a marked effect on their general health, growth, and quality. Expertly covering the science behind the use of prebiotics and probiotics this landmark book explains how the correct manipulation of the gut flora of farmed fishes and crustaceans can have a positive effect on their health, growth rates, feed utilization, and general wellbeing.
Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics provides a comprehensive overview of the current knowledge of the gut microbiomes of fish and their importance with respect to host-fish health and performance, providing in-depth, cutting-edge fundamental and applied information.
Written by many of the world’s leading authorities and edited by Dr Daniel Merrifield and Professor Einar Ringø, this important book discusses in detail the common mechanisms for modulating microbiomes, particularly at the gut level (e.g. probiotics, prebiotics and synbiotics). The book is a key resource for an understanding of the historical development of these products, their known mechanisms of action and their degree of efficacy as presently demonstrated in the literature.
The fundamental material provided on the gut microbiota itself, and more broad aspects of microbe-live feed interactions, provide essential reading for researchers, academics and students in the areas of aquaculture nutrition, fish veterinary science, microbiology, aquaculture, fish biology and fisheries. Those involved in the development and formulation of aquaculture feeds and those with broader roles within the aquaculture industry will find a huge wealth of commercially-important information within the book’s covers. All libraries in universities and research establishments where biological sciences, nutrition and aquaculture are studied and taught, should have copies of this excellent book on their shelves.
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Table of Contents
Title Page
Copyright
List of Contributors
Preface
Chapter 1: The Gastrointestinal Tract of Fish
1.1 INTRODUCTION
1.2 ANATOMY OF GI TRACT
1.3 STOMACH AND INTESTINAL BULB
1.4 PYLORIC CAECA
1.5 INTESTINE
1.6 ENDOGENOUS INPUTS OF DIGESTIVE SECRETA
1.7 LUMINAL pH
1.8 PASSAGE RATE AND RESIDENCE TIME
1.9 ACKNOWLEDGEMENTS
REFERENCES
Chapter 2: Immune Defences of Teleost Fish
2.1 INTRODUCTION
2.2 INNATE IMMUNITY
2.3 ANTIGEN-SPECIFIC ADAPTIVE IMMUNITY
2.4 CYTOKINES DRIVE IMMUNE RESPONSIVENESS
2.5 IMMUNE TISSUES
2.6 MUCOSAL IMMUNITY
2.7 COMMON PATHOGENS INFECTING TELEOSTS: WHAT IMMUNE RESPONSES ARE REQUIRED?
2.8 FUTURE CONSIDERATIONS
2.9 CONCLUSION
REFERENCES
Chapter 3: Gastrointestinal Pathogenesis in Aquatic Animals
3.1 INTRODUCTION
3.2
VIBRIO
spp.
3.3
AEROMONAS
spp.
3.4
YERSINIA RUCKERI
3.5
EDWARDSIELLA
spp.
3.6
PISCIRICKETTSIA SALMONIS
3.7
PSEUDOMONAS ANGUILLISEPTICA
3.8
PHOTOBACTERIUM DAMSELA
subsp.
PISCICIDA (PASTEURELLA PISCICIDA)
3.9 STREPTOCOCCOSIS
3.10 ‘
CANDIDATUS ARTHROMITUS
’
3.11
MYCOBACTERIUM
spp.
3.12 CONCLUSION
REFERENCES
Chapter 4: The Gut Microbiota of Fish
4.1 INTRODUCTION
4.2 THE IMPORTANCE OF THE MICROBIOTA
4.3 COMPOSITION OF THE MICROBIOTA IN EARLY LIFE STAGES
4.4 FACTORS THAT INFLUENCE MICROBIOTA COMPOSITION
4.5 CONCLUSION
REFERENCES
Chapter 5: Methodological Approaches Used to Assess Fish Gastrointestinal Communities
5.1 CULTURE-DEPENDENT APPROACHES
5.2 MOLECULAR TECHNIQUES
5.3 FLUORESCENCE BASED METHODS
5.4 ELECTRON MICROSCOPY
5.5 MICROBIAL ACTIVITY AND FUNCTIONALITY
5.6 SUMMARY
5.7 ACKNOWLEDGEMENTS
REFERENCES
Chapter 6: Indigenous Lactic Acid Bacteria in Fish and Crustaceans
6.1 INTRODUCTION
6.2 LACTIC ACID BACTERIA
6.3 SALMONIDAE
6.4 GADIDAE
6.5 CLUPEIDAE
6.6 ANARHICHADIDAE
6.7 ACIPENSERIDAE
6.8 PERCIDAE AND SCIAENIDAE
6.9 MORONIDAE
6.10 SPARIDAE
6.11 PLEURONECTIFORMES
6.12 CYPRINIDAE
6.13 CHANNIDAE
6.14 SILURIFORMES
6.15 CICHLIDAE
6.16 SERRANIDAE
6.17 RACHYCENTRIDAE
6.18 MUGILIDAE
6.19 COASTAL FISH
6.20 SHELLFISH
6.21 SUMMARY
REFERENCES
Chapter 7: Probiotics and Prebiotics: Concepts, Definitions and History
7.1 INTRODUCTION
7.2 THE PROBIOTIC CONCEPT AND HISTORY
7.3 THE PREBIOTIC CONCEPT AND DEFINITION
7.4 SYNBIOTICS
7.5 SUMMARY
REFERENCES
Chapter 8: Probiotic Modulation of the Gut Microbiota of Fish
8.1 INTRODUCTION
8.2
BACILLUS
spp.
8.3 LACTIC ACID BACTERIA (LAB)
8.4 OTHER PROBIONTS
8.5 PROBIOTIC COLONIZATION?
8.6 CONCLUSION AND FUTURE PERSPECTIVES
8.7 ACKNOWLEDGEMENTS
REFERENCES
Chapter 9: Probiotic Applications in Cold Water Fish Species
9.1 INTRODUCTION
9.2 SALMONIDAE
9.3 GADIDAE
9.4 PLEURONECTIFORMES
9.5 PERCIDAE
9.6 CONCLUSION
REFERENCES
Chapter 10: Probiotic Applications in Temperate and Warm Water Fish Species
10.1 INTRODUCTION
10.2 EUROPEAN SEA BASS (
DICENTRARCHUS LABRAX
L.)
10.3 GILTHEAD SEA BREAM (
SPARUS AURATA
L.)
10.4 Probiotic Applications In Sole Spp.
10.5 GROUPERS
10.6 TILAPIA
10.7 CARPS
10.8 ZEBRAFISH (
DANIO RERIO
)
10.9 CATFISHES
10.10 GENERAL CONCLUSIONS
REFERENCES
Chapter 11: Probiotic Applications in Crustaceans
11.1 INTRODUCTION
11.2 MAIN MICROORGANISMS EVALUATED AND USED AS PROBIOTICS IN CRUSTACEAN AQUACULTURE
11.3 PROBIOTIC MODES OF ACTION
11.4 RELATED BENEFITS IN CRUSTACEAN AQUACULTURE
11.5 CONCLUSION
REFERENCES
Chapter 12: Can Probiotics Affect Reproductive Processes of Aquatic Animals?
12.1 INTRODUCTION
12.2 THE FISH REPRODUCTIVE SYSTEM
12.3 BROODSTOCK REPRODUCTIVE DYSFUNCTIONS
12.4 REPRODUCTION AND METABOLISM
12.5 THE EFFECTS OF PROBIOTIC APPLICATIONS ON FISH REPRODUCTION
12.6 CONCLUDING REMARKS
12.7 ACKNOWLEDGEMENTS
REFERENCES
Chapter 13: Issues with Industrial Probiotic Scale-up
13.1 INTRODUCTION
13.2 SCALING-UP GUIDELINES
13.3 MODE OF ADMINISTRATION
13.4 PROBIOTIC REGISTRATION
REFERENCES
Chapter 14: Prebiotics in Finfish: An Update
14.1 INTRODUCTION
14.2 SALMONIDAE
14.3 GADOIDS
14.4 ACIPENSERIDAE
14.5 CYPRINIDAE
14.6 SILURIFORMES
14.7 MORONIDAE
14.8 SPARIDAE
14.9 CICHLIDAE
14.10 SCIAENIDAE
14.11 OTHER FISH SPECIES
14.12 SYNBIOTICS
14.13 CONCLUDING REMARKS AND FURTHER PERSPECTIVES
REFERENCES
Chapter 15: Prebiotic Applications in Shellfish
15.1 INTRODUCTION
15.2 USE OF PREBIOTICS IN SHELLFISH AQUACULTURE
15.3 PREBIOTIC BENEFITS
15.4 CONCLUSION
REFERENCES
Chapter 16: Live Feeds: Microbial Assemblages, Probiotics and Prebiotics
16.1 INTRODUCTION
16.2 BACTERIAL ASPECTS OF LIVE FEED
16.3 BACTERIAL CONTROL OF LIVE FEED CULTURES
16.4 ENRICHMENT OF LIVE FEED AND MICROBIAL IMPLICATIONS
16.5 PROBIOTICS IN LIVE FEED PRODUCTION
16.6 BIOENCAPSULATION OF PROBIOTICS IN LIVE FOOD AND DELIVERY TO LARVAE
16.7 PREBIOTICS AND SYNBIOTICS IN LIVE FEED
16.8 CONCLUSIONS AND FUTURE PERSPECTIVES
REFERENCES
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Figure 1.1
Figure 1.2
Figure 1.3
Figure 1.4
Figure 1.5
Figure 1.6
Figure 1.7
Figure 2.1
Figure 2.2
Figure 3.1
Figure 3.2
Figure 3.3
Figure 3.4
Figure 3.5
Figure 3.6
Figure 4.1
Figure 4.2
Figure 4.3
Figure 4.4
Figure 4.5
Figure 4.6
Figure 5.1
Figure 5.2
Figure 6.1
Figure 7.1
Figure 7.2
Figure 7.3
Figure 8.1
Figure 8.2
Figure 8.3
Figure 8.4
Figure 10.1
Figure 12.1
Figure 12.2
Figure 12.3
Figure 12.4
Figure 12.5
Figure 12.6
Figure 13.1
Figure 15.1
Figure 16.1
List of Tables
Table 3.1
Table 4.1
Table 4.2
Table 5.1
Table 5.2
Table 6.1
Table 6.2
Table 6.3
Table 8.1
Table 8.2
Table 8.3
Table 8.4
Table 8.5
Table 9.1
Table 9.2
Table 9.3
Table 9.4
Table 10.1
Table 10.2
Table 10.3
Table 10.4
Table 10.5
Table 10.6
Table 10.7
Table 10.8
Table 11.1
Table 11.2
Table 12.1
Table 12.2
Table 14.1
Table 14.2
Table 14.3
Table 14.4
Table 14.5
Table 14.6
Table 14.7
Table 14.8
Table 14.9
Table 14.10
Table 15.1
Table 16.1
Aquaculture Nutrition:Gut Health, Probiotics and Prebiotics
Edited by
Daniel Merrifield
School of Biological Sciences, Plymouth University, UK
Einar Ringø
Norwegian College of Fishery Science, UiT The Arctic University of Norway
This edition first published 2014 © 2014 by John Wiley & Sons, Ltd
Registered office: John Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
Editorial offices: 9600 Garsington Road, Oxford, OX4 2DQ, UK
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Library of Congress Cataloging-in-Publication Data
Aquaculture nutrition : gut health, probiotics, and prebiotics / edited by Daniel Merrifield and Einar Ringo.
pages cm
Includes bibliographical references and index.
ISBN 978-0-470-67271-6 (cloth)
1. Fishes— Digestive organs. 2. Fishes— Health. 3. Fishes— Nutrition. 4. Marine animals— Digestive organs. 5. Marine animals— Health. 6. Marine animals— Nutrition. 7. Aquaculture. I. Merrifield, Daniel, 1983- II. Ring?, Einar, 1950-
QL639.1.A685 2014
571.1′7— dc23
2014015269
A catalogue record for this book is available from the British Library.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
Cover image: Photos by Daniel Merrifield.
List of Contributors
José Luis Balcázar
Catalan Institute for Water Research (ICRA), Scientific and Technological Park of the University of Girona, Spain
Jarl Bøgwald
Norwegian College of Fishery Science, UiT The Arctic University of Norway, 9037 Tromsø, Norway
E-mail:
Oliana Carnevali
Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy
E-mail:
Mathieu Castex
Lallemand SAS, 19 rue des Briquetiers, BP 59, 31702 Blagnac Cedex, France
E-mail:
Liet Chim
IFREMER, Département Aquaculture en Nouvelle-Calédonie, BP 2059, 98846 Nouméa Cedex, New Caledonia
Roy Ambli Dalmo
Norwegian College of Fishery Science, UiT The Arctic University of Norway, 9037 Tromsø, Norway
E-mail:
Carly Daniels
The National Lobster Hatchery, South Quay, Padstow, Cornwall PL28 8BL, UK
Simon J. Davies
Aquatic Animal Nutrition and Health Research Group, School of Biological Sciences, Plymouth University, Plymouth, Devon, UK
Arkadios Dimitroglou
Nireus Aquaculture SA, R&D Department, 26 Silivrias str., GR-34100 Chalkida, Greece
E-mail:
Henri Durand
Lallemand SAS, 19 rue des Briquetiers, BP 59, 31702 Blagnac Cedex, France
Matthew Emery
Aquatic Animal Nutrition and Health Research Group, School of Biological Sciences, Plymouth University, Plymouth, Devon, UK
Andrew Foey
School of Biomedical and Healthcare Sciences, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK
E-mail:
Giorgia Gioacchini
Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy
E-mail:
Elisabetta Giorgini
Dipartimento di Scienze della Vita e dell'Ambiente, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy
Seyed Hossein Hoseinifar
Department of Fisheries, Gorgan University of Agricultural Science and Natural Resources, Gorgan, Iran
Hélène L. Lauzon
Primex ehf, Siglufjordur, Iceland
E-mail:
Mark R. Liles
Department of Biological Sciences, Auburn University, Auburn, Alabama, USA
Pavlos Makridis
Biology Department, University of Patras, 26500 Patras, Rio, Greece
Daniel L. Merrifield
Aquatic Animal Nutrition and Health Research Group, School of Biological Sciences, Plymouth University, Plymouth, Devon, UK
E-mail:
Bernadette Okeke
Lallemand SAS, 19 rue des Briquetiers, BP 59, 31702 Blagnac Cedex, France
Tania Pérez-Sánchez
Laboratory of Fish Pathology, Faculty of Veterinary Medicine, Universidad de Zaragoza, Zaragoza, Spain
Simona Picchietti
Department for Innovation in Biological, Agro-food and Forest Systems, University of Tuscia, Largo dell'Università s.n.c., 01100 Viterbo, Italy
E-mail:
José Pintado
Instituto de Investigacións Mariñas (IIM-CSIC), Eduardo Cabello no. 6, 36208 Vigo, Galicia, Spain
E-mail:
Miquel Planas
Instituto de Investigacións Mariñas (IIM-CSIC), Eduardo Cabello no. 6, 36208 Vigo, Galicia, Spain
Arun Kumar Ray
Fisheries Laboratory, Department of Zoology, Visva-Bharati University, Santiniketan-731 235, West Bengal, India
E-mail:
;
Einar Ringø
Norwegian College of Fishery Science, UiT The Arctic University of Norway, 9037 Tromsø, Norway
E-mail:
Jaime Romero
Laboratorio de Biotecnología, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, Santiago, Chile
E-mail:
Yun-Zhang Sun
Key Laboratory of Healthy Mariculture for the East China Sea, Ministry of Agriculture, Fisheries College, Jimei University, Xiamen 361021, PR China
Lisa Vaccari
SISSI Beamline, ELETTRA Synchrotron Light Laboratory, S.S. 14, km 163.5, 34149, Basovizza, Trieste, Italy
Paul Waines
Aquatic Animal Nutrition and Health Research Group, School of Biological Sciences, Plymouth University, Plymouth, Devon, UK
Bin Yao
Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, PR China
Zhigang Zhou
Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, PR China
Preface
Since the initial investigations on the gut microbiota of fish some five decades ago, considerable information has been presented on their composition, abundance, diversity and activity. Numerous studies have demonstrated that these communities are complex and generally of low cultivability, containing Bacteria, Archaea, viruses, yeasts and protists. However, little attention has been paid to the Archaea, protists or viruses but several studies have revealed diverse communities of bacteria and yeast. These microbes have major implications on host health, development, welfare and nutrition and therefore great efforts have been made in the past two decades to fortify these communities and maintain microbial balance. Among such efforts the applications of probiotics and prebiotics have been at the forefront. The scientific evidence which underpins the efficacy, and to some extent elucidates their modes of action, has been comprehensive, although not always reproducible. This body of evidence has helped to create a market and drive demand for commercial probiotics and prebiotics for use in aquaculture operations globally. As such, many feed manufacturers, multi-nationals and small domestic operations, routinely add pro- and prebiotic products to their feed formulations. The extent of their economic benefits is not yet clear, as such information is not often openly discussed by fish farmers, but the increasing demand and increasing volumes of probiotic/prebiotic aquafeeds produced are positive indicators for industrial level applications. Future research efforts should focus on better understanding of the modes of action, which must include a better understanding of the composition and activity of indigenous microbiomes, as well as the effects on the host itself, so that optimisation of probiotic/prebiotic selection, dosage and application strategies can occur.
The chapters within this book address these issues and are advised reading for an understanding of the historical development of these products, their known mechanisms of action and their degree of efficacy as presently demonstrated in the literature. We also hope that the fundamental material provided on the gut microbiota itself, and more broad aspects of microbe-live feed interactions, are useful reading for researchers, academics and students. We wish to thank the authors that have contributed to this book, as well as our PhD students and post-doctoral staff whom have also assisted in the collection of data and literature. We are also grateful to the assistance of the production staff at Wiley-Blackwell for their support.
Daniel Merrifield and Einar Ringø
Chapter 1The Gastrointestinal Tract of Fish
Arun Kumar Ray1 and Einar Ringø2
1Department of Zoology, Visva-Bharati University, West Bengal, India
2Norwegian College of Fishery Science, UiT The Arctic University of Norway
ABSTRACT
The organization of the gastrointestinal (GI) tract of fish follows the basic features as in other vertebrate groups with a degree of variation in phylogeny and ontogeny, feeding habits, diet, nutrition, physiological conditions and the special functions the gut may perform. There are enormous variations in the morphology of the GI tract among various fish species. The variations in the organization of the GI tract ensure optimum utilization of dietary nutrients, which in many cases means efficient primary digestion and a large intestinal absorptive surface area. Different fish species have adapted different approaches to accommodate this objective. Of particular interest to fish nutritionists is the comparison of morphological features in relation to natural diets. In order to compare data obtained from one fish species with other species, it is essential to make divisions into a broad line of common morphological features.
1.1 INTRODUCTION
Detailed descriptions of the anatomy and physiology of GI tracts of numerous fish species have been covered in several reviews (Suyehiro 1942; Barrington 1957; Kapoor et al. 1975; Harder 1975; Fänge and Grove 1979; Smith 1989; Stevens 1988; Olsen and Ringø 1997; Wilson and Castro 2011). Fish have the ability to rapidly and reversibly adapt GI tract characteristics to match the changes in functional demands that occur during their life history (e.g. metamorphosis, anadrome or catadrome migrations) or more frequently (day-to-day or seasonal shifts in diet or environmental conditions); this ability is dependent on endocrine signalling pathways which are augmented by the enteric nervous system (Karila et al. 1998). The wide diversity and levels of hormones and signalling molecules secreted by the numerous types of GI tract and endocrine pancreas cells allow fish to rapidly and reversibly alter characteristics of the GI tract and other organ systems to adapt to changes in the contents of the GI tract (amounts and types of nutrients, pH, ionic composition etc.) and environmental conditions (Holst et al. 1996).
The key feature of the alimentary tract is its ability to digest foodstuffs to make them suitable for absorption by various transport mechanisms in the wall compartments of different GI sections (Bakke et al. 2011). Besides the hydrolytic reactions catalysed by endogenous enzymes secreted by the pancreas and cells in the gut wall, which are considered to play the major roles in digestion, fermentation plays key roles in digestive processes in many monogastrics. The role of fermentation in fish is less clear due to a lack of knowledge, but it is considered to be of minor quantitative importance for nutrient supply in cold water species. However, qualitative importance may be significant regarding specific nutrients and immune stimulating processes.
The anatomy and physiology of the GI tract are important determinants for the establishment and for the quantitative as well as the qualitative aspects of its microbiota. The microbial communities may seem to be assembled in predictable ways (Rawls et al. 2006). In this study the authors showed that microbial communities transplanted from mice to gnotobiotic zebrafish (Danio rerio) alter quantitatively in the direction of the normal biota of the zebrafish species and vice versa. This indicates that environmental conditions of the intestine, determined by species-specific parameters along the GI tract such as anatomy, endogenous inputs of digestive secretions, pH, osmolality, redox potential, compartment size and structure, passage rate and residence time, help to define and shape the GI tract microbiota. However, diet composition is also an important environmental condition for fish development. Diet composition is ideally species specific regarding available essential nutrients, but supplies variable amounts of unavailable material depending on the feedstuffs used in the diet formulations. The gut microbiota is also probably inevitably linked to digestion by the production of exogenous enzymes and vitamins produced which might aid host digestive function (Ray et al. 2012). This chapter summarizes the current state of knowledge highlighting the morphological and histological variations in the lower GI tract of fish associated with digestion and absorption; comprehensive reviews on the gut microbiota are presented in Chapters 4–6.
1.2 ANATOMY OF GI TRACT
The structure and functional characteristics of the GI tract vary widely among species (Suyehiro 1942) and seem, to a great extent, to match the wide diversity of feeding habits and environmental conditions exploited by fish. The structure of the alimentary canal varies in different species of fish, and is generally adapted in relation to the food and feeding habits. Depending on feeding habits and diet, fish are generally classified as carnivorous (eating fish and larger invertebrates), herbivorous (consuming mainly plant material), omnivorous (consuming a mixed diet) and detritivorous (feeding largely on detritus) (De Silva and Anderson 1995; Olsen and Ringø 1997; Ringø et al. 2003), together with the genera Panaque and Chochliodon which are capable of digesting wood. However, such division may not always be correct since most species consume mixed diets or their feeding habits may change through the life cycle (Olsen and Ringø 1997). The variation becomes obvious by comparing the GI tract characteristics of carnivorous and herbivorous fish and those from freshwater and seawater. The mucosal lining of the GI tract represents an interface between the external and internal environments, and in conjunction with the associated organs (e.g. pancreas, liver and gall bladder) provides the functions of digestion, osmoregulation, immunity, endocrine regulation of GI tract and systemic functions, and elimination of environmental contaminants and toxic metabolites. The GI tract is basically a tube that courses through the body. The GI tract in Atlantic cod (Gadus morhua L.) is shown in Figure 1.1. This tract is divided into the following characteristic regions: mouth, gill arch, oesophagus, stomach, mid intestine, distal intestine and fermentation chamber.
Figure 1.1 The alimentary tract of Atlantic cod (Gadus morhua L.). ST, stomach; PC, pyloric caeca; F, proximal intestine; M, mid intestine; B, distal intestine; HC, fermentation chamber.
(Source: Lisbeth Løvmo Martinsen.)
1.3 STOMACH AND INTESTINAL BULB
Two main groups of fish are commonly distinguished on the basis of presence or absence of stomach. The most remarkable feature of the digestive system of lampreys, hagfish, chimaeras, and many herbivorous fishes belonging to Cyprinidae, Cyprinodontidae, Balistidae, Labridae, Scomberesocidae and Scaridae, is the lack of a true stomach. In cyprinids, for example mrigal (Cirrhinus mrigala), the anterior part of the intestine becomes swollen to form a sac-like structure called the intestinal bulb or pseudogaster (Figure 1.2). In the absence of a stomach, the anterior intestine performs the function of temporary storage of ingested food (Sinha 1983). In stomachless fish the intestinal bulb apparently secretes mucus, and histologically the mucosa resembles closely that of the intestine and is devoid of any digestive components (Horn et al. 2006; Manjakasy et al. 2009). The mucosa of the intestinal bulb is thrown into prominent folds or villi (for lack of a better term; strictly speaking they are not true villi due to the absence of lacteals) that are lined with absorptive and mucus-secreting cells. The absence of stomach in many stomachless fish is compensated by the presence of pharyngeal teeth or gizzards for grinding food (Suyehiro 1942; Fänge and Grove 1979). Wood-eating fishes have specifically adapted spoon-shaped teeth for efficiently rasping wood (Nelson et al. 1999). The lack of a stomach in some species of fish raises questions regarding its significance. Several hypotheses have been put forward to explain the absence of a stomach which are often contradictory and speculative (for review, see Wilson and Castro 2011). The shape, size and structure of the stomach, when present, are related to the duration between meals and the nature of the diet (Suyehiro 1942; Smith 1989; De Silva and Anderson 1995). A stomach is defined as a portion of the digestive tract with distinctive cell lining, where acid is secreted, usually along with some digestive enzymes like pepsin (Olsen and Ringø 1997). In his early study, Suyehiro (1942) classified stomachs of fish into five categories according to their morphological appearance: (a) straight tube (Pleuronectidae, Esox), (b) U-shape (Salmonids), (c) V-shape (Plecoglossidae, Mugilidae, Salmonidae, Sparidae), (d) Y-shape (Mugilidae, Clupeidae), and (e) I-shape (Carangidae, Gadidae, Scombridae, Serranidae). The highest degree of modifications of the pyloric stomach have been reported in several members of Clupeoidei, Channidae, Mugilidae, Acipenseridae, Coregoninae and Chanidae (milkfish, Chanos chanos) where it acts as a ‘gizzard’ for trituration and mixing (Fänge and Grove 1979; Kapoor et al. 1975; Buddington 1985; De Silva and Anderson 1995). This development of a ‘gizzard’ has been attributed to microphagy, and is thought to partly compensate for poor dentition (Pillay 1953). The anterior part of the stomach (cardiac or fundic region) is characterized by the presence of gastric glands (Figure 1.3A) and the musculature is also usually more prominent (De Silva and Anderson 1995). The stomach mucosa is lined with columnar epithelium and studded with minute depressions, the gastric crypts or pits that lead into the tubular or alveolar gastric glands. Gastric glands are present in abundance throughout the cardiac stomach, so much so that they occupy the entire mucosal layer beneath the superficial epithelium (Figure 1.3A). This part of the stomach is secretory in nature and is responsible for storage and initial physical and enzymatic breakdown of the diet; readers with special interest in this topic are referred to the comprehensive review of Bakke et al. (2011). The mucosa of the posterior part of the stomach (pyloric stomach) contains many mucus-producing tubular mucus glands or pyloric glands (Figure 1.3B). The number of these glands decreases considerably in the middle region and they are completely absent in the posterior region. The pyloric stomach is completely devoid of gastric glands. The pH of the stomach therefore varies and in salmonids it is between 3.0 and 4.5 (Ransom et al. 1984; Gislason et al. 1996).
Figure 1.2Alimentary tract of the mrigal (Cirrhinus mrigala). IB, intestinal bulb; PI, proximal intestine; MI, mid intestine; DI, distal intestine. Relative intestinal length (RIL) is 14–15.
(Source: Arun K. Ray.)
Figure 1.3 Transverse section through different regions of the GI tract of climbing perch, Anabas testudineus, a carnivorous perch. (A) Cardiac stomach. GG, gastric glands. Arrows indicate mucus-secreting cells at the free borders of columnar epithelial cells. ×400 magnification. (B) Pyloric stomach. Arrows indicate tubular mucus glands or pyloric glands. ×400 magnification. (C) The intestine. GC, goblet cell. Arrows indicate absorptive cells. ×400 magnification. (D) The pyloric caeca. ×400 magnification.
(Source: Ray and Moitra 1982.)
To our knowledge, the stomach microbiota is less investigated. Austin and Al-Zahrani (1988) evaluated bacteria in the stomach of rainbow trout (Oncorhynchus mykiss Walbaum) by using electron microscopy, while Navarrete et al. (2009) and Zhou et al. (2009a) evaluated the stomach microbiota of Atlantic salmon (Salmo salar L.) and emperor red snapper (Lutjanus sebae Cuvier), respectively, by molecular methods.
1.4 PYLORIC CAECA
In a number of fish species, several finger-like outgrowths develop from the anterior part of the intestine in the region of pylorus. These are called pyloric caeca or intestinal caeca, and open into the lumen of the intestine. They are located proximal in the midgut region, and, when present, number from a few as in murrel Channa punctatus (Figure 1.4) to several hundred as in Atlantic cod (Figure 1.1). The caeca of different species vary considerably in size, state of branching and connection to the gut (Suyehiro 1942; Olsen and Ringø 1997; Ringø et al. 2003). Histologically, they closely resemble the intestine (Figure 1.3D), and possibly serve to increase the absorptive surface of the gut (Bergot et al. 1975). The pyloric caeca are always absent in stomachless fish (Barrington 1957; Kapoor et al. 1975). Although the presence or absence of the pyloric caeca has no apparent correlation with the nature of the food or with feeding habits (Khanna 1961; Mohsin 1962), the caeca are typically absent or much reduced in omnivorous and herbivorous species (Rust 2002). There is also no clear correlation between the number of caeca and the length of the gut, and feeding habits (Harder 1975; Hossain and Dutta 1996). Pyloric caeca have been reported to increase the surface area for digestion and absorption but do not have any role in fermentation or storage (Buddington and Diamond 1987). In salmonids, the pH of caeca and caecal intestine is 7.0 and 7.5, respectively (Ringø et al. 2003). Compared to the numerous studies evaluating the finfish gut microbiota (e.g. Cahill 1990; Ringø et al. 1995; Ringø and Gatesoupe 1998; Hansen and Olafsen 1999; Ringø and Birkbeck 1999; Austin 2006; Kim et al. 2007; Merrifield et al. 2011; Lauzon and Ringø 2012), fewer studies have investigated the microbiota of pyloric caeca (Lesel and Pointel 1979; Gildberg et al. 1997; Gildberg and Mikkelsen 1998; Navarrete et al. 2009; Zhou et al. 2009b).
Figure 1.4 Alimentary tract of murrel (Channa punctatus). ST, stomach; PC, pyloric caeca; PI, proximal intestine; DI, distal intestine. Relative intestinal length (RIL) is 0.5.
(Source: Arun K. Ray.)
1.5 INTESTINE
In fish, the intestine is the main organ for digestion/absorption. In addition to digesting and absorbing feedstuffs, the intestine is critical for water and electrolyte balance, endocrine regulation of digestion and metabolism, and immunity (Ringø et al. 2003). The intestine shows considerable variation in its length and arrangement in different species of fish (Kapoor et al. 1975; Fänge and Grove 1979; Stevens 1988). Some fish have a relative intestinal length (RIL = length of intestine/length of body) less than 1, while some fish species have an RIL of 10 to 20 times their body length (Suyehiro 1942; Olsen and Ringø 1997). The highest RIL generally occurs in herbivorous and detritivorous species (Figure 1.2), while the lowest is found in strictly carnivorous and predatory species (Figures 1.1 and 1.4). The intestine in Cyprinids and Loricariids exhibits a wide range of looping and coiled arrangements (Figure 1.5), while omnivorous species show an intermediate condition. There are also differences in RIL within the same species. For example, in kalbasu (Labeo calbasu) the RIL of the detritivorous adult is higher (2.1 to 13.0) than that of fry feeding on zooplankton (0.5 to 1.0) (Sinha 1976). It is assumed that the long intestinal length of herbivorous compared to carnivorous fish is due to the requirement for digesting and absorbing the portion of the plant food which they normally ingest in the adult stage (Sinha and Moitra 1975). The greater length and mass of the intestine in herbivores relative to carnivores have also been thought to allow for additional processing of relatively difficult-to-digest items (Horn 1997; Clements and Raubenheimer 2005). However, it is also possible that herbivorous and/or detritivorous fish consuming plant fibres and detritus depend on extended intestines in order to increase the utilization efficiency, which is not directly related to the surface area (Olsen and Ringø 1997). On the contrary, Harder (1975) opined that there are no clear relationships between intestinal morphology and feeding type and it is not possible to draw any conclusion in this regard. Histologically, the intestine in fish contains simple, columnar absorbing epithelium lined with brush border of microvilli, which is typical of absorptive tissue (Figure 1.3C; De Silva and Anderson 1995) and goblet cells (mucus producing cells). In some fish species regional variations in the brush border formations have been observed (Figure 1.6). The numbers of goblet cells are more numerous in the posterior region than in the anterior and middle regions (Ray and Moitra 1982). The posterior part of the intestine is considered to be the main site for intestinal absorption of macromolecules in salmonids and some other fish species (for review, see Dalmo et al. 1997; Figure 1.7). The midgut starts immediately posterior to the pylorus and the hindgut is an extension of the midgut with gradually diminishing digestive and absorptive functions and increased level of mucus production (Ringø et al. 2003).
Figure 1.5 Alimentary tract of detritivorous mrigal (Cirrhinus mrigala) showing extremely coiled intestine.
(Source: Arun K. Ray.)
Figure 1.6 Transmission electron microscopy images from the intestine of tilapia Oreochromis niloticus (A and B) and zebrafish Danio rerio (C and D). Images show the regional variation in the brush border formation (microvilli length and abundance) between the anterior (A and C) and posterior (B and D) intestine. Gc, goblet cell; L, lumen; M, mitochondria; Mb, cell membrane; Mv, microvilli; Tj, tight junction. Scale bar = 1 µm.
(Source: Merrifield and Harper, unpublished.)
Figure 1.7 Scanning electron microscopy images from the posterior intestine of rainbow trout Oncorhynchus mykiss, depicting the mucosal folds (or ‘villi’). Scale bars = 50 µm.
(Source: Merrifield and Dimitroglou, unpublished.)
1.6 ENDOGENOUS INPUTS OF DIGESTIVE SECRETA
Different enzymes, bile acids and pancreatic enzymes are constantly secreted or leaking into the GI tract from the wall tissue and from the liver and pancreas, respectively. These fluids contain a great range of compounds that may affect the growth and composition of the intestinal microbiota. Besides macromolecules such as a great number of proteins, for example digestive enzymes and muco-polysaccharides, these fluids contain phospholipids, bile acids, antioxidants such as glutathione, minerals, waste products eliminated from the body through the faeces (e.g. bilirubins giving colour to the faeces) and bicarbonate to stabilize the pH of the luminal contents. Although our knowledge is limited for fish, it can be suggested that these fluids vary greatly in quantity as well as composition between intestinal segments and within species under different conditions. To our knowledge, no information has been reported in the scientific literature regarding quantities of water and material entering the GI tract of juvenile or adult fish. However, alterations in composition have been observed, and information is available that alterations are observed in activities of digestive enzymes within the gut contents of salmonids by incorporation of plant material in the diet (Romarheim et al. 2006; Gatlin III et al. 2007; Santigosa et al. 2008) as well as alterations in content of bile acids caused by dietary fibre (Romarheim et al. 2006). Various dietary components may serve as substrates for the gut microbes, and enzymes such as proteases and lipases, bile acid and antimicrobial components will also probably modulate the gut microbiota.
1.7 LUMINAL pH
Information on the pH of digesta along the GI tract of finfish is not well described in the scientific literature. In the stomach the pH values can be below 4, while in the pyloric region and the mid and distal intestine they are above 7 and mostly above 8. The pH of the chyme seems to be regulated within fairly narrow ranges. In the stomach, pH seem to be higher in Atlantic salmon (Gislason et al. 1996) compared to mammals (pH 2; Madigan and Martinko 2006). This difference in pH may be of relevance for microbial survival and colonization in the stomach. No marked decrease in the distal intestine has been observed as might have been expected if the microbial activity was high.
1.8 PASSAGE RATE AND RESIDENCE TIME
The passage rate and residence time in the various sections along the GI tract influence the microbial community and subsequently the host and the host–microbial interactions. Stomach evacuation rate and passage time through the intestine have been observed to vary with temperature, meal size, particle size, feed composition, previous nutritional history, fish size and stress (Fänge and Grove 1979; Bromley 1994). Diet is also known to affect passage time (Storebakken et al. 1999) and hence may affect microbial colonization in the gut. To our knowledge, no information is available on the relationship between gut microbiota colonization, gut passage rate and residence time, and this topic merits further investigations.
1.9 ACKNOWLEDGEMENTS
The authors are grateful to Dr Merrifield, Dr Dimitroglou and Mr Harper for providing their unpublished micrographs.
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Chapter 2Immune Defences of Teleost Fish
Andrew Foey1 and Simona Picchietti2
1School of Biomedical and Healthcare Sciences, Plymouth University, UK
2Department for Innovation in Biological, Agro-food and Forest Systems, University of Tuscia, Viterbo, Italy
ABSTRACT
Teleost fish have a well-established innate immune response that is vital for anti-pathogen responses in their antigen-rich environment. With the increase in scientific investigations and the availability of specific reagents, it is clear that these fish also possess pathogen/antigen-specific adaptive responses. These responses are comparable to those of higher organisms, responding to intracellular and extracellular resident pathogens, initiating cell-mediated immunity (CMI) and humoral defences, respectively. This chapter reviews the current understanding of teleost immunity, with particular emphasis on the tissues involved in immune development (thymus, head kidney and spleen) and those under most antigenic stimulation – the skin and mucosal surfaces. In this context, an understanding of teleost immune defences is important for our comprehension of the health benefits conferred by prebiotics and probiotics introduced in feed formulations.
2.1 INTRODUCTION
Teleost fish exhibit a well-developed immune system; they possess a rapid and efficient innate immune system and, in addition, display characteristics of an adaptive antigen-specific immunity which would appear to have all the traits of established mammalian systems but reacts at a much slower rate which is, in part, due to the lower local environmental temperatures. By the nature of their habitat, fish live in an antigen-rich environment and as such their immune systems are continually being challenged by both commensal and pathogenic organisms. It is thus vital that these fish can either recognize beneficial microbes and induce a state of non-responsiveness/tolerance, or activate immune anti-microbial defences to pathogens which are predominantly led by a rapid innate immune response and ideally followed by an antigen-specific adaptive response which will afford a more tailored response to a pathogen upon secondary exposure. The relative paucity of reliable, specific reagents to components of the teleost fish immune system has resulted in slow progress in the understanding of immune defences in these fish. Although studies have characterized the presence of immune cells and molecules, they are rarely consolidated by functional studies and, as such, some of our understanding of fish immunology has been obtained by matching observations in the fish system with inferences from more comprehensively characterized mammalian immune systems. The aim of this chapter is to review the current understanding of the immune system in teleost fish in the context of how innate, adaptive and mucosal barrier defences deal with the wide array of pathogenic organisms present in the fish's environment.
2.2 INNATE IMMUNITY
The aquatic environment of teleost fish, by its very nature, is rich in pathogens and antigenic stimuli. As a result, it is vital that the fish immune system is capable of a rapid and robust immune response capable of protecting the host from the plethora of pathogenic insults. To cope with this, teleosts have a well-developed innate immune system which is particularly strong with respect to barrier/mucosal defences. The barriers which are constantly under attack or challenge by such an antigen-rich environment include the skin and the mucous membranes of the gills and the intestinal tract. Epithelial cells are at the forefront of these barrier defences and function as both a physical barrier and an immune instructor, capable of perpetuating either immune tolerance in homeostatic conditions or immune activation in response to pathogen invasion. These cells can protect the host by innate defences which include the secretion of anti-microbial molecules such as lysozyme, cathelicidins, cathepsins and defensins. These serve to break down pathogen cell walls, hence killing them and preventing their multiplication. If this barrier defence is compromised, then the pathogen is faced with a barrage of underlying defences which include a plethora of cellular and soluble components. These innate defences include cells such as macrophages and neutrophils involved in phagocytosis, complementing production and expression of innate inflammatory cytokines; each displays different effector functions which are dependent on the immune cell being activated and by the pathogen activation molecules encountered.
The immediate lines of defence, prior to epithelial cells and those of the underlying innate immune cells, consist of a physical barrier of commensal bacteria and mucus. Commensal bacteria are integral to mucosal immunity and will be covered later in this chapter and in following chapters. In general, commensal bacteria compete with pathogenic microbes for nutrients, binding sites on epithelial cells, and can modulate the immune system to benefit the host. Mucus is also vital to host protection and is produced at mucosal surfaces such as the gills and intestinal tract as well as the external surface of the skin. Mucus exists in a state of constant translocation, being physically removed from the skin and mucosal surfaces, hence trapping and removing pathogens and preventing their attachment to and invasion of host cells (reviewed in Ellis 2001). Skin mucus acts as a lubricant, is involved in locomotion and osmoregulation, and plays a role in the prevention of colonization by pathogens such as bacteria, fungi and parasites. Its biochemical properties afford it chemical defence (Jakowska 1963). The basic components of mucus include macromolecular mucin components (mucopolysaccharides) and glycoproteins. In general, mucus contains many different types of secretory substances with a wide variety of functions. These secretory substances include the antibacterial peptides (pleurocidin, piscidins, trypsin-like proteases, cathepsins L and B, lysozyme and β-defensins), c-reactive protein (CRP), lectins (involved in carbohydrate recognition, resulting in agglutination, opsonization and complement activation) and immunoglobulins, which confer passive immunity on newly hatched fry who mucus-feed from parental skin (Hildemann 1959; Buckley et al. 2010).
In addition to the barrier defence associated epithelial cells, the main effector cells of the teleost innate immune system include neutrophils, monocytes, macrophages and granulocytes such as basophils, eosinophils, mast cells/eosinophilic granule cells (MCs/EGCs) and rodlet cells. All of these play a role in inflammatory responses to acute or chronic infection. The neutrophils and macrophages function as phagocytes in the recognition and clearance of pathogenic materials, and when activated can release anti-microbials as part of the respiratory burst and cytokines to instruct other parts of the immune response (reviewed in Rombout et al. 2010). Rodlet cells are thought to be immature eosinophilic granulocytes that play a significant role in defence against parasites; rodlet cell numbers increase in the presence of helminths where aggregations have been observed in infected epithelia of the gills and intestinal tract. MCs/EGCs possess both acidophilic and basophilic granules; these cells are recruited and observed in high numbers in chronically inflamed tissues. Degranulation results in the secretion of acid and alkaline phosphatases, tryptase, nucleotidases, 5-HT, lysozyme and peptide antibiotics (piscidins and pleurocidin). Recruitment, activation and degranulation of these cells have been described in response to the bacterial infection of Aeromonas salmonicida, Renibacterium salmoninarum and nematode infestation of intestinal tissue (reviewed in Reite and Evensen 2006).
The first step in activation of innate immune effector functions is the recognition of pathogens and their antigens. Pathogen recognition occurs in response to a broad array of conserved pathogen-associated molecular patterns (PAMPs) expressed by the pathogen; these in turn are recognized by their innate counterparts, the pattern recognition receptors (PRRs). This array of PRRs exists as both secreted and membrane-associated recognition receptors. In general, the secreted PRRs include collectins, pentraxins, complement components and mannose binding lectin (MBL). The membrane-associated PRRs exist as either signalling receptors or binding receptors for clearance by phagocytosis. The secreted PRRs such as lectins (MBL, interlectin and pentraxins) and complement components are involved in opsonization, phagocytosis, chemotaxis, inflammation and pathogen killing. The lectin class of molecules is involved in recognition of sugar moieties expressed by pathogens and not normally expressed on host tissues. This class of molecules consists of the collectin MBL, which activates complement cascades via the lectin pathway. MBL recognizes mannose, fucose and N-acetyl-D-glucosamine, acting as an opsonin for recognition and phagocytosis as well as activating serine proteases for proteolytic breakdown (Nakao et al. 2006). The pentraxin molecules are composed of five identical subunits and include CRP and SAA. CRP binds phosphocholine moieties of certain bacterial and fungal cell wall lipopolysaccharides, resulting in the activation of the complement cascade via binding to C1q. Another class of lectin molecule has been identified in teleost fish, namely interlectin (reviewed in Vasta et al
