In all intensive livestock farming, diseases present a challenge. Efforts to keep farmed fish free of diseases are important both for fish welfare and for the economy of the fish farmer.
In the early days of Norwegian aquaculture, the high incidence of bacterial infection in salmon and rainbow trout resulted in severe losses. Treatment with antibiotics was necessary to inhibit the spread of the infections, reduce mortality and keep fish welfare as optimally high as possible.
All farmed salmon are vaccinated
Frequent outbreaks of disease, high mortality and treatments with antibiotics led to severe economic losses for fish farmers. In addition, the concentration of antibiotics under the cages and bacterial resistance to the antibiotics used led to intensive research into effective vaccines against the most important fish diseases. Today, all farmed salmon in Norway are vaccinated and thus most bacterial infections are prevented.
The most important viral infections in salmon farming today are Infectious Pancreatic Necrosis, Infectious Salmon Anaemia, and Pancreatic Disease, against which there is no treatment. The available vaccines against viral infections in fish are still not as effective as most vaccines against bacterial infections. To prevent or reduce the impact of viral diseases, good management practice is essential. With regard to Infectious Salmon Anaemia, the authorities have issued strict regulations on how to handle outbreaks of the infection using slaughtering and fallowing periods.
Developmental anomalies, deformities and cataracts have to date been the most significant among the non-infectious diseases. Research has shown that temperatures in early developmental stages and nutritional factors are important in avoiding these problems.
Parasites may be found among farmed fish, as in wild populations. Salmon lice (Lepeotheirus salmonis) are the most common parasite among all species of salmonids.
Low total use of antibiotics
Among other marine species in aquaculture, diseases are a challenge just as in the salmon industry. Their larvae are very small compared to the salmon fry at hatching and are especially vulnerable in this initial period. Hence good hygienic conditions are crucial in the production of early life stages. Antibiotics are used to treat bacterial infections and most of the antibiotics used in fish farming in Norway today are used to fight diseases in marine species, although their total use is low. Vaccines against infections have also been developed for marine species.