Like land-based forms of raising livestock, where large numbers of animals are placed in a very limited space, intensive fish farming provides various diseases and parasites ideal conditions to spread. Infectious diseases like furunculosis were previously treated with large quantities of antibiotics added to feed. In our discussion of the environmental impacts of antibacterial agents in fish farming, we would remind the reader that the use of antibiotics in the Norwegian fish farming industry has fallen from 50,000 kilograms to 500-600 kilograms in fifteen years (Grave et al., 2002). ). According the Norwegian Institute of Public Health statistics the antibiotic use in fish farming was at its lowest in 1999 with 591 kg. Since that time the use has increased to a top in of 1,428 kg in 2006 and a reduction to 649 kg in 2007.

The biodegradation of antibiotics in the sediments goes relatively slowly (a half-life of up to 150 days in the topmost sediment layer, 0-1 cm), but varies substantially among the various agents and among types of sediment. A study in which samples were taken up from under various fish farms indicates that Florfenicol has a half-life a fraction of that of the other common agents (Hektoen et al., 1995)

Important to focus on antibiotics
The environmental impacts of high levels of antibiotic use in fish farming will be substantial and unwanted. Therefore, it is good news that the use of antibiotics in the Norwegian fish farming industry has nearly been eliminated in fifteen years, from 50 tonnes to about 1,000 kilograms. Nonetheless it is important to keep the focus on this issue in countries where the development of vaccines and general preventive health efforts have not come as far, and where considerable antibiotic use continues to be maintained.