HATCHERY Feed & Management Vol 10 Issue 2 2022

Page 29


Micro-dose vaccines: Why less is more Giulia Faè, Socorex Isba SA

Over the past two decades, aquaculture has grown at an average annual rate of approximately 8%. In 2014, the contribution of aquaculture to supply food for human consumption overtook wild-caught fish for the first time. This unprecedented growth of global aquaculture has not been free of challenges.

From antibiotics to preventive medicine in aquaculture The vaccine against enteric redmouth disease (caused by Yersinia ruckeri, a gram-negative bacteria) developed in the 1970s was the first to become commercially available. During the past 20 years, fish vaccines have become an established and cost-effective method of controlling several viral and bacterial infectious diseases. The overall positive effect of vaccination in farmed fish is reduced mortality, making production more predictable and profitable. In Norway, the use of antibiotics has been reduced from 47 tons to approx. 1 ton after vaccination became a common strategy to control bacterial diseases in farmed fish. Viral diseases are more difficult to control (also due to the lack of anti-viral drugs) and have caused catastrophic losses to fish farmers around the globe. Nevertheless, several viral vaccines have been developed in finfish. The Chilean Infectious Salmon Anaemia (ISA) crisis of the first decade of the 21st century was caused by inadequate production management methods, including the failure to vaccinate fish against ISA. The challenge of reducing side effects when injecting Vaccination for aquatic species has three major routes of delivery: injection [intraperitoneal (IP) and intramuscular (IM)], immersion, and oral. Among those methods, vaccination by injection has proven

Vaccinating tilapia with Socorex syringe and FishGuide accessory.

preferable where species allow, having several definite advantages. It provides the most direct delivery of antigens throughout the immune system. The vaccine can be concentrated and delivered in the presence of adjuvants and other beneficial compounds (e.g., carriers, bacterial antigens/cells, etc.) that could not be delivered by other methods. However, despite its high efficiency in generating immunity, injection also has some disadvantages. Inflammation and pigmentation in the abdominal cavity, a prolonged period before fish return to normal feeding and, potentially, downgrading of the fish fillets are possible side effects associated with injectable vaccines. Local reactions may vary from mild, such as very slight adhesions (most frequently around the injection site), or hardly noticeable amounts of melanin on viscera, to severe, including major lesions to the carcass after evisceration. Those affect almost every internal organ in the cranio-dorsal area, often with a considerable amount of melanin, where viscera become unremovable without damaging the integrity of the fillet.

Hatchery Feed & Management Vol 10 Issue 2 2022

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