Tilapia health: quo vadis?

Species and farmed types of tilapia have become one of the world's most popular aquaculture products and provide nutrition and livelihood to rural and urban communities around the world.* This popularity has been due to technological advances in fish health, farming systems, breeding and genetics, engineering, marketing as well as wide consumer acceptance and the special biological characteristics of tilapia that enable them to survive and grow in a variety of environments and farming systems. As the farming of tilapia has become more widespread, so have the concerns around fish health and disease prevention and cure. To review the status of tilapia health, disease prevention and cure, the Food and Agriculture Organization of the United Nations (FAO) and INFOFISH convened a virtual International Technical Seminar, Tilapia health: quo vadis,† that brought together 1700 participants from over 100 countries. A call for expression of interest was released after the event, to develop the presentations into full articles for publication as a Special Issue at Reviews in Aquaculture. Eight groups of authors responded to the call and the eight papers now constitute this Special Issue. The FAO Lead Technical Officer (Melba G. Bondad-Reantaso), guest editors (J.R. Arthur, Devin M. Bartley, Kevin Fitzsimmons, and Michael J. Phillips), authors and entities that funded the papers as Open Access (indicated in individual papers) are gratefully acknowledged. The virtual event was supported by two FAO projects, namely: GCP/RAF/510/MUL Enhancing capacity/risk reduction of emerging Tilapia Lake Virus (TiLV) to African tilapia aquaculture and TCP/INT/3707 Strengthening biosecurity (policy and farm-level) governance to deal with Tilapia lake virus. The special issue builds on the recent review of tilapia published as a special virtual issue in RAQ 15:1 (2023); with articles that focus on fish health issues along with other articles that set the scene for tilapia farming globally. The paper by El-Sayed and Fitzsimmons, From Africa to the World- the Journey of Nile tilapia, documents how Nile tilapia, first farmed by ancient Egyptians 4000 years ago, has been moved from Africa to farming systems around the world to become one of the most important farmed species. The review further reveals that although Nile tilapia often supports inland capture fisheries as well as aquaculture production, tilapia introductions have in some cases adversely impacted local cichlid species, and reduced abundance of other fishery resources. Farmed tilapia producers and processors have been leading the seafood industry in several aspects of processing, value adding, and packaging. The dependable supply and pricing of farmed tilapia and its value in several sectors, for example, food service, fast casual dining, frozen meals, as well as fresh seafood counters, have allowed processors and marketers to invest in novel value-added processing and packaging. This has only been possible because the tilapia industry has invested in advanced production systems and fish health. Much of the tilapia sold in international trade is processed in the producing country. Often fillets are marketed leaving about 70 percent of the fish unused. The paper, How value addition by utilization of tilapia processing by-products can improve human nutrition and livelihood, by Peñarubia and co-authors, reveals a wide range of other products that are or could be utilized in the supply chain. So-called ‘by-products’ of processed tilapia that may be discarded or used for animal feed, can provide additional income to workers in the tilapia supply chain. In addition to nutritious products such as fish cakes and sausage, tilapia skins are processed to produce leather and gelatin, heads and bones can be turned into flour or supplements, and collagen from fish scales and bones have potential in the cosmetic and pharmaceutical fields. The authors point out that further research and development, along with marketing are needed to fully utilize the wide range of products available from tilapia. The paper by Zimmerman and co-authors, The future of intensive tilapia production and the circular bioeconomy without effluents: biofloc technology, recirculation aquaculture systems, Bio-RAS, partitioned aquaculture systems, and integrated multitrophic aquaculture, describes several of the most innovative fish farming systems allowing farmers to grow more fish in smaller areas with fewer inputs. Recirculating systems, aquaponics, bioflocs, in-pond raceways are just some of the more advanced, or intensive, aquaculture methods that were mostly pioneered using tilapia and are now being tested with other species. The paper provides a nice overview of these systems and their particular pro's and con's. In, Strategies to enhance tilapia immunity to improve their health in aquaculture, Wang and co-authors provide an overview of the benefits of enhancing the immune response to improve tilapia health, in turn reducing the levels of pathogens within tilapia farming systems. The authors review the immune system of tilapia and the importance of the gut microbiome. They then summarize the strategies used to reduce the impact of disease in tilapia culture through enhancement of the immune system, including the feeding of probiotic and prebiotic supplements to modulate the gut microbiota, the use of herbal medicines and immunostimulants to enhance immunity to disease, and the existing and potential use of vaccines to prevent infections. They note that emerging and re-emerging diseases such as streptococcosis, tilapia lake virus disease, and infectious spleen and kidney necrosis virus disease have resulted in high levels of morbidity and mortality, production losses and trade restrictions. In the absence of effective husbandry management, disease prevention strategies and appropriate biosecurity measures, these and other infectious diseases will continue to challenge the sustainability of global tilapia aquaculture. They then look at the economics of applying immune enhancement strategies in tilapia culture, noting that the decision to use these products depends on multiple factors including farming practice, farmer perception, and the overall cost-benefits. They note that effective husbandry management through maintaining high water quality, adequate nutrition, and good biosecurity will create a less stressful environment for fish. Rapid response to epidemic events and the availability of rapid and accurate diagnostic methods are important to limit the damage caused by disease. Vaccination as a means of controlling infectious diseases is one of the most significant and successful health practices within the aquaculture industry. The review, Improving tilapia biosecurity through a value chain approach, by MacKinnon and co-authors explores the value chain perspective to assess and manage risks of disease threats and losses in tilapia aquaculture. The paper outlines the tilapia value chain as a starting point, then assesses the important infectious agents of tilapia that may affect different parts in the value chain. The paper then describes how risk analysis can be applied to identify critical control points in the value chain and potential risk mitigation measures that may be implemented at those points. It emphasizes, as many of the other papers illustrate, that the control of diseases of tilapia requires a multi-faceted approach across the whole ‘aquaculture system’, with control measures chosen based on their feasibility, effectiveness and sustainability. In, A global review of problematic and pathogenic parasites of farmed tilapia, Shinn and co-authors provide an extensive and detailed global accounting of the protistan and metazoan parasites of tilapias, with emphasis on those species having demonstrated or potential impact to tilapia aquaculture. The authors summarize more than 2500 host–parasite records from 73 countries and more that 820 recorded tilapia introductions. For each major parasite taxonomic group, they highlight those parasites that have been translocated along with their tilapine hosts or have been acquired from the new environments into which tilapia have been introduced, together with remarks on their taxonomy, reported geographic distribution (including translocations), pathology, status, and future directions of research, and approaches to treatment and control. They note that while Africa has enormous potential for aquaculture development, substantial knowledge gaps about tilapia parasites remain for many African states, which creates associated production and biosecurity risks. Globally, tilapias host a rich fauna of parasites, with new species still being encountered. This review and its associated supplementary tables will be of high value to fish parasitologists in general, to diagnosticians, to tilapia farmers encountering parasite problems in their facilities, and to government scientists conducting import risk analyses for proposals to introduce tilapias to new geographic areas. Tilapia has often been described as extremely hardy fish with very few disease problems. While this is generally true, rearing more and more fish intensively can induce stressful conditions that allow pathogens to take hold and allow a disease to spread. Likewise, fish selected for fast growth, colour morphs and/or body conformation may have allowed some of the innate hardiness to have been degraded. The paper by Haenen and co-authors, Bacterial diseases of tilapia, their zoonotic potential and risk of antimicrobial resistance provides a thorough overview of bacterial diseases and some associated pathologies that have and are affecting commercial farms rearing tilapia. While the losses endured by the tilapia industry have been less than salmon or shrimp farming, no farmer wants to lose fish and see income decline. Treatments and vaccines are described for the various bacteria which have been associated with significant mortalities. In their review, From the basics to emerging diagnostic technologies: What is on the horizon for tilapia disease diagnostics?, Ha Dong and co-authors stress that the intensification of tilapia farming has exacerbated losses due infectious diseases and that the disease diagnostics play a crucial role in aquaculture biosecurity and health management. However, the recent proliferation of cutting-edge molecular methods in aquaculture has shifted the focus of researchers and users away from basic approaches and towards molecular diagnostics, despite the fact that many diseases can be rapidly diagnosed using inexpensive, simple microscopic examination. This review highlights the importance of the three levels of diagnostics for diseases of tilapia to promote the integration of both basic and advanced methods to achieve accurate and meaningful diagnostic results. The authors thus emphasize the need for frequently overlooked but basic procedures such as case history records, gross pathology, presumptive diagnostic methods, and histopathology. They also provide an in-depth review of current and emerging molecular diagnostic technologies for tilapia pathogens, including polymerase chain reaction methods, isothermal amplification methods, CRISPR-based detection, and lateral flow immunoassays. They also discuss the future of tilapia disease diagnostics, including next generation sequencing, artificial intelligence, environmental DNA/RNA and point-of-care testing, and a future vision for transferring these technologies to farmers and stakeholders for a sustainable aquatic food system transformation. Undoubtedly, tilapia, and especially Nile tilapia, will continue to be one of the most important groups of farmed aquatic species. The material reviewed in this special edition provides valuable information to resource managers, fish farmers, processors, marketers, and vendors to help ensure that tilapia aquaculture develops responsibly and provides beneficial outcomes to communities and the environment. Devin M. Bartley: Conceptualization; project administration; writing – original draft; writing – review and editing. J. Richard Arthur: Conceptualization; writing – original draft; writing – review and editing. Kevin Fitzsimmons: Conceptualization; writing – original draft; writing – review and editing. Michael J. Phillips: Conceptualization; writing – original draft; writing – review and editing. Melba G. Bondad-Reantaso: Conceptualization; writing – original draft; writing – review and editing. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.