2 Monitoring of Marine Aquaculture
67
Diseases and ectoparasites have been a problem in the fish-farming industry
since the beginning. Many of the major infectious diseases have however been
combated by vaccination and improved hygiene, which has dramatically reduced
the usage of antibacterial agents. However, sea lice infestations have proved difficult
to overcome and the transfer of sea lice is still considered one of the major problems
in Norwegian mariculture. At all fish farms, sea lice must be counted at least every
second week when the water temperature exceeds 4°C and the results are reported
to the Norwegian Food Safety Authority. If the number of lice per fish exceeds the
threshold limits, the fish farmer is obliged to delouse at the farm (Anon. 2000).
All use of medicines is prescribed by a veterinarian and is registered by the
Norwegian Medicines Control Authority and the Fisheries Directorate. Antibacterial
agents, which were widely administered in the late 1980s, are presently only used
in low amounts mainly on broodstock and early life stages (1,215 kg used in 2005,
The Norwegian Institute of Public Health). Traditionally, sea lice medicines have
been administered as bath treatments, first organophosphates and hydrogen peroxide
and later pyrethroids, but in-feed medicines are becoming more widely used. Chitin
synthesis inhibitors such as teflubenzuron and diflubenzuron were initially
employed on a trial basis, but have not been used since 2002 due to their potential
impact on non-target organisms. Instead, the use of avermectins has increased and
39 kg were sold in 2005 (The Norwegian Institute of Public Health). At the present
there is no mandatory monitoring requirements for medicines and their residues in
the marine environment. However, the environmental authorities may require monitoring
with reference to The Pollution Control Act (Anon. 1981).
The most frequently used chemicals in Norwegian fish-farming are antifouling
compounds for the net pens. The most common is copper, although this compound
is meant to be phased out and of application should be significantly reduced before
2010 in accordance with the Declaration of The Hague of March 1990 (Anon.
1990). However, it has proven difficult to find a substitute, and there are still large
amounts of copper in use. As is the case for medicines, there is no mandatory monitoring
requirement for copper in the sediment but the environmental authorities may
require monitoring with reference to The Pollution Control Act (Anon. 1981).
According to the Environmental Objectives of Norwegian aquaculture, organic
wastes from fish farms must not result in unacceptable effects on the environment
locally or regionally and permitted threshold levels of impact must be determined
(Directorate for Nature Management 1997). Due to large variations in hydrographical
conditions and depth at fish farm sites, the amount of organic waste that settles on
the sediment will vary considerably. Furthermore, the size and the management of
the fish farm will also influence the sedimentation. The impact, such as changes in
sediment chemistry and in the benthic fauna community, will therefore also have a
large variability between sites.
Overloading of sites and accumulation of organic material in the form of waste
feed pellets and faeces can, besides the effects on the environment, be a cause of
stress, poor growth and disease in the farmed fish, with the associated spread of
infectious agents and need for medication. Organic material can therefore be influential
67
Diseases and ectoparasites have been a problem in the fish-farming industry
since the beginning. Many of the major infectious diseases have however been
combated by vaccination and improved hygiene, which has dramatically reduced
the usage of antibacterial agents. However, sea lice infestations have proved difficult
to overcome and the transfer of sea lice is still considered one of the major problems
in Norwegian mariculture. At all fish farms, sea lice must be counted at least every
second week when the water temperature exceeds 4°C and the results are reported
to the Norwegian Food Safety Authority. If the number of lice per fish exceeds the
threshold limits, the fish farmer is obliged to delouse at the farm (Anon. 2000).
All use of medicines is prescribed by a veterinarian and is registered by the
Norwegian Medicines Control Authority and the Fisheries Directorate. Antibacterial
agents, which were widely administered in the late 1980s, are presently only used
in low amounts mainly on broodstock and early life stages (1,215 kg used in 2005,
The Norwegian Institute of Public Health). Traditionally, sea lice medicines have
been administered as bath treatments, first organophosphates and hydrogen peroxide
and later pyrethroids, but in-feed medicines are becoming more widely used. Chitin
synthesis inhibitors such as teflubenzuron and diflubenzuron were initially
employed on a trial basis, but have not been used since 2002 due to their potential
impact on non-target organisms. Instead, the use of avermectins has increased and
39 kg were sold in 2005 (The Norwegian Institute of Public Health). At the present
there is no mandatory monitoring requirements for medicines and their residues in
the marine environment. However, the environmental authorities may require monitoring
with reference to The Pollution Control Act (Anon. 1981).
The most frequently used chemicals in Norwegian fish-farming are antifouling
compounds for the net pens. The most common is copper, although this compound
is meant to be phased out and of application should be significantly reduced before
2010 in accordance with the Declaration of The Hague of March 1990 (Anon.
1990). However, it has proven difficult to find a substitute, and there are still large
amounts of copper in use. As is the case for medicines, there is no mandatory monitoring
requirement for copper in the sediment but the environmental authorities may
require monitoring with reference to The Pollution Control Act (Anon. 1981).
According to the Environmental Objectives of Norwegian aquaculture, organic
wastes from fish farms must not result in unacceptable effects on the environment
locally or regionally and permitted threshold levels of impact must be determined
(Directorate for Nature Management 1997). Due to large variations in hydrographical
conditions and depth at fish farm sites, the amount of organic waste that settles on
the sediment will vary considerably. Furthermore, the size and the management of
the fish farm will also influence the sedimentation. The impact, such as changes in
sediment chemistry and in the benthic fauna community, will therefore also have a
large variability between sites.
Overloading of sites and accumulation of organic material in the form of waste
feed pellets and faeces can, besides the effects on the environment, be a cause of
stress, poor growth and disease in the farmed fish, with the associated spread of
infectious agents and need for medication. Organic material can therefore be influential