6
Aquaculture in North Carolina ~ Rainbow Trout
Much of the labor on
the farm is used to
stock, grade, transfer
and harvest fish, all
of which occur year-
round.
limiting, the use of an oxygenation system is
a means of more intensively using tank
space and increasing farm production,
sometimes by as much as 50% or more.
Although supplemental oxygen is a proven
means of increasing profits, the high initial
investment deters farmers. Initial investment
in equipment is estimated to be $4,000 to
$6,000 per pair of tanks, or $40,000 to
$60,000 for the example farm in Trout
Budgets.
It is assumed that the farm in Trout
Budgets is located in a site with a year-
round supply of high quality water, and
does not use supplemental oxygen.
Medication
Like any crop or livestock, trout are
susceptible to disease. Stress increases the
probability that an animal will not be able to
effectively stave off the onset of an
infectious disease. Crowding, improper
handing, low dissolved oxygen, and sudden
changes in temperature are factors which
create stress and can lead to disease
problems. The best method of disease
prevention is to protect trout from exposure
to sources of stress.
Trout are affected by bacterial, parasitic,
and viral pathogens. Bacterial infections are
treated with feed containing antibiotics.
Parasites are typically treated with
chemicals applied directly to tank water. No
medication is effective against viral
pathogens. The most common viral infection
is pancreatic necrosis, which affects fish
less than 3 in size, and is confined to
hatchery facilities.
The costs of all medication and chemicals
constitute less than 1% of the variable costs
of growing trout. Trout Budgets assume
that 5% of feed is medicated feed and that
$100 annually is spent on chemical treatments.
Electricity
The use of electricity is typically confined
to lighting of the raceways. The cost of
installing electrical lines is very site specific,
ranging from zero to tens of thousands of
accounting for about 70% of total
variable cost.
Trout farmers rely on feed tables which
are provided by the Cooperative Extension
Service or feed manufacturers. These tables
indicate the amount to feed based on the fish
size and water temperature. Trout feed
actively and convert feed most efficiently at
water temperatures between 55°F and 65°F.
Feeding in excess of what the fish are able
to metabolize increases the costs of
production, and leads to deterioration of
water quality and disease.
Most farms in NC use a combination of
hand feeding and feed distributed by
demand feeders. Demand feeders consist of
plastic cylinders suspended over each tank,
with a rod hanging from the bottom of the
cylinder into the water. Fish quickly become
adept at moving the rod, which causes feed
to fall from the cylinder. A few farmers use
automatic feeders, which dispense feed
from a hopper at preset intervals rather than
in response to movement by the fish.
Oxygen
As discussed above in Water, the amount
of oxygen in water limits the production
capacity of a farm in two ways: by limiting
the number of raceway tanks that can be
used in a series, and by limiting the density
at which fish can be stocked.
One in five of NC trout farmers use some
means of supplemental oxygen. Some use
oxygen on an emergency basis, renting
oxygen tanks only during the summer
months when feeding rates are higher and
flow rates lower, both of which can lower
the oxygen content in raceway water.
Successful use of oxygen assumes that
oxygen is the factor which limits raceway
loading and production for a given site and
set of raceways. Often other elements
water temperature, accumulation of solids,
level of carbon dioxide or ammoniamay be
the limiting factor to production, and in this
case an oxygenation system would not be
the means by which the farmer could
increase production. When oxygen is
Trout Budgets
estimate costs and
return to a facility
consisting of 20
tanks, producing
60,480 pounds of fish
annually.