Fish as food. / Volume 1, Production, biochemistry, and microbiology
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More different species imply a more efficient use of resources. The opportunities for an invader to find a niche in a highly diverse ecosystem is thus considerably decreased.
Fish As Food. Volume 1: Production, Biochemistry,and Microbiology. Book • . Edited by: GEORG BORGSTROM. Browse book content. About the book. Fish as Food, Volume I: Production, Biochemistry, and Microbiology discusses Contents of Volumes II and III 1. Biology of Seafish Production I. Introduction II.
In rich communities it is more likely that at least one of the community members has an antagonistic activity against pathogenic invaders. It seemed that a lower diversity in the microbial rhizosphere community in dwarf wheat led to a higher susceptibility to invasion by Pseudomonas.
Unfortunately, as far as known, no information is available concerning the effect of microbial evenness on the resistance against infections in the intestinal environment of aquatic larvae. Rr, Do and Dy values that are beneficial to fish larvae are not established yet, as too little systematic data are available on their microbial communities.
Hence in the future, processing fingerprinting data as described above will need to prove its value. A considerable number of studies have been published testing the virulence of various pathogens to marine fish larvae of different species. Testing of virulence through challenge experiments provides useful information on a given bacterium, for instance on whether it should be considered a primary pathogen i.
Anecdotal information about bacteria being isolated from diseased marine larvae has limited value as evidence for virulence. The authors concluded that anecdotal information about bacteria being isolated from diseased marine larvae is of limited value as evidence for virulence.
Challenge studies can be divided according to the method of administration of pathogens, depending on whether oral challenge or bath challenge has been used. Challenge experiments with unfed fish larvae i. A multiwell assay is relatively simple, provides a high number of replicates with one larva per well. However, such assays are limited to administration by bath, and must be terminated at the point of first feeding.
Oral challenge of fish larvae during the first feeding stages includes experimentally manipulating a model food chain. Challenge experiments need to be complemented by other methods in order to provide information on processes related to virulence, such as adhesion, penetration and proliferation in larval tissues. Histological methods, supplemented with tools that can identify the pathogen, such as immunofluorescence and immunohistochemistry can provide such information.
In situ methods are means to verify the presence of the pathogen in given larval tissues. In situ hybridization techniques detect not only the presence of a pathogen, but the active transcription of its genes. In challenges with viral pathogens, this method provides important additional information, as evidence of viral replication. For instance, Biering and Bergh studied infectious pancreatic necrosis virus IPNV in halibut, using immunohistochemistry to detect the presence of the virus in different larval organs, and in situ hybridization to detect transcription, hence viral replication.
Sequential sampling, followed by histological and immunohistochemical processing of the sections can provide similar information on uptake, spreading and proliferation within the host. Use of transformed bacteria with fluorescent reporter genes combined with methods such as confocal microscopy of whole larvae has been suggested by several researchers.
Such methods could provide higher sensitivity than immunofluorescence, and could also be adapted to viral pathogens. Teleostei is one of three infraclasses in the class Actinopterygii, which roughly makes up half of the extant vertebrate species, with high biodiversity, and they occupy a key evolutionary position in the development of immune responses.
They are the earliest class of vertebrates possessing the elements of both innate and adaptive immunity.
In most fish, passive immunity is characterized by the presence of lytic enzymes, mainly lysozyme, and adaptive factors such as hormones and immunoglobulin. Thus, it is well recognized that along all the early stages of fish development, innate immunity plays a continuous role in orchestrating quick immune responses and protects larvae against the hostile environment, even when their own immunological capacity is still severely limited. In regard to fish larvae, innate defences are of particular commercial relevance.
To overcome this immunological limitation, the evolutionary processes have provided fish innate immunity with wide capacities and mechanisms of protection that are activated just after egg fecundation, and become fully functional by the time of hatching. It is generally accepted that physical barriers are critical in maintaining osmotic equilibrium, in avoiding invading pathogens reaching the circulation and in triggering an extensive network of secondary innate immune responses.
Several studies have been conducted on the nature and functionality of mucosal secretion.
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Among the physical barriers is the digestive tract, which, in addition to being a barrier against infections and environmental toxins, is actively involved in digestion, nutrient absorption, hormone secretion and immune function. Therefore, plasticity of this barrier shall be high and cells making up the gut must be highly specialized to discriminate among the huge amount of antigens that a fish may encounter throughout its life. Furthermore, in the teleost embryo, the close interaction of the gills with the external environment renders them susceptible to infection and they can serve as portals of entry for most bacterial pathogens.
It is worthwhile remembering that thymus also develops from the anterior part of the digestive tract or pharynx, and the developmental processes of the digestive tract and the gills are indirectly linked, because the gill arches develop at the anterior part of the digestive tract, the pharynx. The innate immune system of epidermal structures relies on a wide diversity of immune cells and several biologically active glycoproteins strategically released in tissues directly exposed to the environment. Fish immune cells show the same main features as those of other vertebrates, and lymphoid and myeloid cell families have been determined.
As a consequence, the development of comparative immunology in fish has been hampered by the lack of appropriate markers unequivocally to identify, isolate and functionally characterize the different immune cell types present in different species. However, most of these antibodies have been shown to recognize other immune cells different from the main target as well. Using these innate cellular probes G7 and Mcsf, respectively in microscopical, immunohistochemical and automated flow cytometric analyses allowed correctly to establish the distribution, localization and relative abundance of positive cells during the ontogeny of lymphomyeloid organs in gilthead sea bream.
The responses of innate immunity cells are driven by a diverse array of pattern recognition receptors PRRs that bind molecular motifs, conserved within all classes of microbes. Therefore, it would be expected that any cellular disruption by trauma, releases mitochondrial DAMPs into the circulation with potential to achieve a high concentration and trigger an uncontrolled downstream innate immune signaling response.
It might be interesting to test whether the recognition of endogenous danger signals is conserved in fish and how the recognition mechanisms affect fish innate immunity. Fish innate immunity signaling pathways show a higher level of complexity than those in mammals. Zebrafish genes corresponding to many mammalian PRRs, have been identified and are often present with several paralogs.
As a consequence, this may allow for the recognition of a larger repertoire of PAMPs, or for more specific responses to individual molecular motifs. Furthermore, there is evidence that not all zebrafish TLRs have the same PAMP specificity or signaling activity as their mammalian counterparts. The interaction of a given PAMP with its specific TLR activates a signaling cascade leading to the expression of inflammatory cytokines and chemokines and to the activation of antimicrobial host defence mechanisms, such as the production of reactive nitrogen and oxygen radicals and antimicrobial peptides Fig.
To date, 17 teleost TLRs TLR1, 2, 3, 4, 5, 5S, 7, 8, 9, 13, 14, 18, 19, 20, 21, 22, 23 have been identified by genome and transcriptome analysis and remarkably distinct features of the TLR cascades among fish species have been reported.
Microbiology of Finfish and Finfish Processing | SpringerLink
Simplified scheme of fish innate immune TLRs signaling pathways. Fish detects microbial invaders through highly specific pattern recognition receptors, called TLRs.
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Recent molecular evidence has clearly identified the presence of TLRs in more than a dozen teleost species Palti However, information on the functional ontogeny is limited. To clarify this issue, some laboratory trials have been conducted at the embryo and larval stages on selected fish species. Together, these results demonstrate that most TLRs signalling mechanisms start their functional activity mostly in the first few hours after fecundation which indicates the important role these PRRs play in fish larva immune surveillance. Cytokines are the key regulators of the immune system.
However, detailed studies should be conducted, mostly in molecular biology but including functional in vivo analyses, before making definitive conclusions. In the past few years, a huge increase in the knowledge of the cytokine network has been reported, mainly based on cDNA libraries, EST, and sequenced fish genomes of pufferfish, green spotted pufferfish, medaka, stickleback and zebrafish.
The presence of MCs has been reported in all classes of vertebrates, including fish, amphibians, reptiles, birds, and mammals. Just recently, fish MCs have been noted to respond by migration and degranulation Fig.
Fish As Food V1
However, a definite functional characterization of fish MCs has not been published yet. Besides basic similarities, granules of fish MCs were believed until few years ago to contain components common to their mammalian counterparts such as antimicrobial peptides, lytic enzymes or serotonin, but lack the presence of histamine. From the negative fraction of the analysed population, two different eosinophilic cell types were found in connective tissue, although neither eosinophilic cell types nor acidophilic granulocytes of gilthead seabream showed the metachromatic staining characteristic of mammalian MCs after being stained with toluidine blue at low pH.
Surprisingly, this was true only in species belonging to the largest and most evolutionary advanced order of teleosts, the Perciformes. Furthermore, functional studies indicated that fish professional phagocyte function may be regulated by the release of histamine from MCs upon H1 and H2 receptor engagement. These observations indicate that histamine is biologically active and can regulate the inflammatory response of fish by acting on professional phagocyte signaling.
A similar pathway has not been reported in fish so far. Degranulation of mast cells in response to pathogens. Upon activation by pathogens, mast cells migrate to specific tissues to undergo degranulation of preformed or newly synthesized products showing specific time patterns and increasing target specificity, which ultimately lead to mast cell survival and proliferation.
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Antimicrobial peptides AMPs are host defence effector molecules that probably occur in all life forms, and starting from birth play a key role in fish innate immunity. Since long ago, they have been reported effectively to combat infections caused by viruses, bacteria, fungi and parasites Yano However, recently, an increasing number of AMPs produced by fish e.
Antimicrobial peptides are typically present in fish mucosal surfaces and skin, which represent major routes of entry of pathogens see Smith and Fernandes for a review. Thus, it can be expected that among AMPs, piscidins shall be a fundamental innate strategy in controlling host—microbial interactions at the early larval stages.