Salmonid Antibacterial Immunity: An Aquaculture Perspective

SIMPLE SUMMARY: Capture fisheries are reaching their limit, so the increasing demand for fish protein can only be met through aquaculture. One attractive sector within this industry is the culture of salmonids, which are a) uniquely under pressure due to overfishing and b) the most valuable finfish per unit of weight. The culture of these animals is threatened by many diseases, some caused by bacteria, which can result in large financial losses for fish farmers. Unfortunately, the current methods for the control of aquatic bacterial diseases are either unsustainable (antibiotics) or not very effective (vaccines). This is primarily due to a lack of knowledge surrounding the successful immune function of fish. To improve vaccine design and other methods of control, a deeper understanding of fish immunology is essential. This review highlights the current understanding of fish antibacterial immunity in the context of salmonid culture. Additionally, the successes and shortcomings of current methods used to combat bacterial diseases in salmonid aquaculture will be addressed. Improving our understanding of the salmonid immune system will help to reduce aquaculture losses in the future. ABSTRACT: The aquaculture industry is continuously threatened by infectious diseases, including those of bacterial origin. Regardless of the disease burden, aquaculture is already the main method for producing fish protein, having displaced capture fisheries. One attractive sector within this industry is the culture of salmonids, which are (a) uniquely under pressure due to overfishing and (b) the most valuable finfish per unit of weight. There are still knowledge gaps in the understanding of fish immunity, leading to vaccines that are not as effective as in terrestrial species, thus a common method to combat bacterial disease outbreaks is the use of antibiotics. Though effective, this method increases both the prevalence and risk of generating antibiotic-resistant bacteria. To facilitate vaccine design and/or alternative treatment efforts, a deeper understanding of the teleost immune system is essential. This review highlights the current state of teleost antibacterial immunity in the context of salmonid aquaculture. Additionally, the success of current techniques/methods used to combat bacterial diseases in salmonid aquaculture will be addressed. Filling the immunology knowledge gaps highlighted here will assist in reducing aquaculture losses in the future.