Adverse Effects of Fish Vaccines

Fish diseases remain to be a serious economic threat in commercial aquaculture across the world, despite several innovative approaches to novel therapy. Although antibiotics or chemotherapeutics are used to treat fish diseases, they exhibit some obvious disadvantages, such as drug resistance and safety concerns. Vaccination is regarded as an effective prophylactic measure to prevent a wide range of bacterial and viral infections in aquaculture. Fish immunization has been practiced for more than 50 years and is well recognised as an efficient means of avoiding a variety of infectious diseases of fishes. It can activate the specific and non-specific immune systems of fishes and provide long-term protection. Though vaccination is vital for preventing disease outbreaks and reducing antibiotic usage, it may also have adverse effects on the vaccinated animal, environment or the consumers of vaccinated fishes. It varies with the type of vaccine, mode of administration, environmental parameters, size, stress and immunity of fishes, etc. Inflammation, abdominal lesions, growth retardation, spinal deformities and systemic and autoimmunity development are the major adverse effects associated with injection vaccination in fishes. Apart from this, adjuvants used along with vaccines are also reported to induce granuloma in all the vital organs. Midtlyng and Speilberg scales are used as a standard method for measuring the severity of the lesions developed during fish vaccination. Vaccination is undoubtedly the most effective intervention for disease prevention and control. However, the negative consequences must be considered when creating alternative safe techniques. The present chapter deals with the major adverse effects associated with fish vaccination and their significance in vaccine development.