Vaccination strategies in seawater cage culture of salmonids.

Successful vaccination depends both on the development of protective vaccines and their correct use. In addition to deciding which diseases to vaccinate against, the choice of the method, timing, and use of revaccination must be considered. In seawater culture of salmonids, vibriosis and furunculosis are the most important diseases against which to vaccinate in many parts of the world, while cold-water vibriosis is of great significance in Atlantic salmon in some areas with low water temperatures. A vaccine against infectious pancreatic necrosis (IPN) has also been introduced recently. For optimal protection of salmonids in sea-water, vaccination should be carried out some time before sea transfer, in order to give immunity sufficient time to develop, and to avoid handling stress during smoltification. On the other hand however, vaccination should not be carried out too early, as the degree of immunity declines with time. Water temperature is an important factor when deciding when to vaccinate. Recent research has demonstrated that Atlantic salmon may be vaccinated successfully at low water temperatures. In general, vaccination by the injection method gives superior protection. Vaccines against the Vibrio-infections can also be administered successfully by immersion. However, due to lower levels of immunity, the need for a booster vaccination is greater when such a method is used. As regards vaccines against furunculosis, adjuvants are needed in order to achieve good protection, and, consequently, administration by injection is the only option.