from the BC ( canada)  salmon farmers  association.

What are the ingredients in fish feed? [go to top]
The primary ingredients in salmon feed are fish meal and fish oil made
from
natural sources such as anchovies and herring. Other ingredients
include
wheat or grains used as binding agents. Some feeds also contain a
pigment
that provides the red coloration of the flesh that consumers demand.
The
pigment, either astaxanthin or canthaxanthin, is derived from yeast or
is
synthetically produced from pigment which occurs naturally in the
wild.

Salmon farmers use a combination of antibiotics and husbandry
practices to
combat diseases. Antibiotic use is declining with production of new
and more
effective vaccines, stress minimization, selective breeding,
domestication
of fish and advancements in husbandry practices. In Norway, antibiotic
use
was cut by over 96% between 1990-94 with the introduction of
consistent
fallowing, single year class siting and other specific husbandry
practices.
How are antibiotics used on salmon farms? [go to top]
In general, salmon farming is one of the least medicated forms of
agriculture. Antibiotics are not used on a continual, long-term basis
as
they often are in other types of animal husbandry. Rather, in most
cases
they are used over short periods (5-14 days) to control outbreaks of
disease. As much as possible, salmon are treated in early stages of
growth.
Antibiotics are administered in fish feed and, since antibiotics are
costly,
they are used sparingly. Medicated feed, like all other feed, is given
in
concentrations and amounts formulated to avoid wastage.

. The government regulates and monitors farmed fish to ensure that the
antibiotics completely clear out of the fish's system before they are
sent
to market.

What antibiotics or chemicals are used? [go to top]
Only three antibiotics are licensed for use in specifically treating
fish
diseases: Oxytetracycline, Romet-30 and Tribrissen. Veterinarians can
prescribe a limited number of other theraputants, approved for
treating
other types of animals, in what is known as off-label use. Under these
circumstances, the veterinarian takes professional responsibility for
the
drug's effectiveness and clearance from the fish. Antibiotic residuals
are
very low, and they completely clear from fish bodies in a matter of
days or
weeks.

Aside from antibiotics, there are very few chemicals used in fish
farming.
Anesthetics are used to treat a few gallons of water when fish are
sampled,
weighed and measured. Pigments in the feed are either from natural
sources
such as yeast or krill or synthetic forms of the same pigments.

note that BC might have the advantage to produce 90 % ( i think i
read) of
salmon feed and that other countries might not have the abundance of
sealife
to produce their own feed and might use more unaturel (for salmon )
food
source than herring and anchovies and maybe more grains.
note that the molecules of wheat and other foreign molecules (to the
ocean)
and antibiotics enter the wild food chain from the uneaten food
falling on
the sea floor.
jean-claude