Journal of Fisheries & Livestock Production
Open Access

Immune defence mechanism; Aquaculture; Environmental elements; Fish diseases

Introduction

Biologically and economically efficient methods are used in aquaculture operations to generate a big quantity of healthy fish. As a result, disease prevention is crucial to the sector. The burden of disease on aquaculture has been greatly diminished in recent years thanks to the development of more efficient vaccinations, improved fish nutrition, and improved fish health management strategies [1, 2]. However, there is still a lot that is unclear about fish immunity. Innate and acquired immune responses are both a part of the immune systems of vertebrates. Vaccines rely on an immune response that develops over time after being exposed to the virus. Innate immunity is the body’s first line of defence against infection and works independently of antibodies. The innate reaction is quick and doesn’t need to have been exposed to pathogens beforehand, in contrast to the learned response. Several proteins have direct antibacterial activity, or they can function as opsonins to inactivate infections and encourage macrophage or complement-mediated elimination [3, 4]. This recognition event serves as the foundation for innate immunity and is the initial step in the immediate host defence against infection. Numerous invertebrates and vertebrates have been found to have innate immune defences. Even in mammals, which have robust acquired immune responses, innate immunity is crucial for disease defence.

An organism is shielded from sickness by the immune system, which also controls the growth of tumours and recognises and gets rid of pathogens [5, 6]. Participating in processes that keep circumstances steady during growth and development, after an inflammatory response, or after tissue damage is a crucial function of the immune system.

The innate and adaptive immune systems make up the traditional divide of the immune system. Both invertebrates and vertebrates have an inherent system, which is an ancient evolutionary mechanism. It is made up of germ-line encoded, generally non-specific recognition criteria that exhibit quick action but brief duration. The genetic makeup and evolutionary history of the innate system influence how it will react to pathogens, and environmental variables and pathogenic relationships have shaped this response over time [7, 8]. Therefore, the inherent defense’s specificity is a trait that can be passed down through the generations.

In evolutionary terms, the adaptable arm is a relatively recent development and is thought to have first evolved in jawed vertebrates, or early true fishes, 400–500 million years ago . The emergence of the thymus, B- and T-lymphocytes, and RAG enzymes which, through gene rearrangement, produce the enormous diversity of the immunoglobulin superfamily are crucial developments in the evolution of the adaptive system [9, 10]. These are created somatically, mostly during ontogeny, rather than being germ-line encoded. The pathogen recognition repertoire as a result has nearly infinite variability [11]. Since each person’s immune experience is unique, the specific adaptive response activity is not a trait that can be passed down through the family. The adaptive immune system takes a while to activate because it must choose a specific receptor and produce proteins and grow cells. However, once activated, it remains active for a long time.

Discussion

Food intake by aquatic creatures

According to some theories, the primary selection pressure was the development of the jaw, which led to increased food intake, a higher metabolic rate, greater mobility, and increased exposure to parasites possibly another important factor in the development of the adaptive immune system [12]. Uncertainty exists on the origins of the adaptive system in the invertebrate immune system or other biological characteristics. Candidates that have been mentioned in prochordata include lymphocyte-like cells and viral receptors.

A better knowledge of the structural and functional evolution of the immune system from invertebrates through fish to mammals has been aided, first and foremost, by comparative and developmental research. Fish serve as a useful model for examining the development of the adaptive immune system, and because it frequently takes a while for an adaptive immune response to manifest after an infection, fish are also a fascinating model for exploring how the innate and adaptive immune systems interact [13].

The demand of the fish farming businesses is the next factor, which has also attracted the most funding. The past two to three decades have seen a global increase in aquaculture, which has necessitated the development of thorough understandings of the immune systems of several fish species with significant economic value [14]. The goal was to develop and enhance preventative methods like immunisation and probiotics, as well as to ensure the best possible activity of the fish’s natural immune system through cultural conditions and the selection of fish stock.

The current review’s objective is to investigate the immune system of fish, as well as the internal and external variables that affect its effectiveness, the primary pathogenic dangers, and immunoprophylactic treatments. In this overview, some of the major immune system components of fish were examined, along with the impact of internal and external variables on fish immune function [15]. The relationship between the host and the infection was looked at for a few of the major fish illnesses. It was also looked at how probiotics, immunisation, and immunostimulation can influence the immune system.

For the sake of conciseness, a number of facets of this topic have been omitted or just briefly discussed. For instance, aquaculture has a continuing interest in genetic breeding programmes. These programmes have also involved selecting features for disease resistance, particularly in commercially valuable species including salmonids, sea bass, sea bream, catfish, flounder, tilapia, and cod [16]. These programmes have primarily been applied to cultural traits such as growth and feed conversion.

Large-scale live fish studies are now prohibited due to heightened awareness of animal welfare. For instance, intense scrutiny is currently being directed at large-scale challenge tests related to vaccine trials. To find genetic variations that might affect disease resistance, this has prompted the adoption of molecular technologies like microarray. Breeding trials are another application for this strategy [17]. However, it requires the availability of genetic maps, which is still absent or constrained for fish species utilised in industrial aquaculture. The use of genetically well-defined and manageable species like zebra fish, medaka, fugu, puffer fish species, guppy, and stickleback as suitable models is being done till these are accessible.

Conclusion

Examining the potential impacts of the aquaculture sector on the environment and on wild fish has become more important as people’s views toward environmental issues have changed. Therefore, there are additional challenges that need to be addressed, such as monitoring and assessing changes in immunological parameters, wild and farmed fish’s disease resistance, and changes in water quality.

Recent years have seen significant advancements in our understanding of fish disease immunological control, which has benefited the expanding aquaculture business globally and also improved comprehension of some fundamental immunological processes. The influence of external and internal factors like temperature and stress on the immune response of fish, as well as the variety of responses of various fish species to the same or different infections, have both been established and consistently validated as crucial components in this field of study.

Conflict of Interest

None

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