THE FARMING

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THE FARMING Powered By Docstoc
					Commercial Catfish Production
Feeds and Feeding
Nutrient requirements and feeding
characteristics of channel catfish have
been extensively researched. This research
has provided the basis for the formulation
of efficient, economical diets and for the
development of feeding strategies - both of
which have been instrumental in the
success of the catfish industry.
Photo of feed. Nutrition
Catfish farmers are able to feed a
nutritionally complete diet that provides
required levels of nutrients and energy in a
readily digestible form. It is essential to
provide a complete diet because catfish can
synthesize only a small portion of the
required nutrients and the quantity of
nutrients from natural food organisms in
the pond is relatively small. Forty nutrients
have been identified as necessary for the
normal metabolic function of channel
catfish.
Based on current knowledge, a digestible
energy to crude protein (DE/P) ratio of 8.5-
10 kcal/gram is adequate for use in
commercial catfish feeds. Ratios above this
range may lead to increased fat deposition
and if the energy ratio is too low, the fish
will grow slowly.
Catfish feeds contain grain or grain by-
products that are rich in starch.

 In addition to providing an inexpensive
energy source, starch helps bind feed
ingredients together and increases
expansion of extruded feeds so that the
feed pellets are water stable and float in the
water.

A typical catfish feed contains 25 percent
or more of digestible carbohydrates.
Lipid levels in commercial catfish feeds
rarely exceed 5-6 percent.

 About 3-4 percent of the lipid is inherent
in the feed ingredients, with the remaining
1-2 percent being sprayed onto the finished
pellets to reduce feed "fines".

 Both vegetable and animal lipids have
been used for pellet coating.
Considerable work has been conducted
over the last 10 years concerning the level
of dietary protein and amino acids needed
for cost effective growth.

 Data from these studies indicate that the
dietary protein requirement for various life
stages of catfish ranges from about 25-50
percent.
 Recent studies have indicated that a
protein level of 28 percent is adequate for
growout when fish are fed to satiation.
Catfish feed are generally supplemented
with a vitamin premix to meet dietary
requirements and to compensate for losses
due to feed manufacture and storage.

Catfish feeds are also supplemented with
phosphorus and a trace mineral premix.
However, there is evidence that
supplemental trace minerals may not be
need in diets using animal proteins.

Feeds

There are various types of catfish feeds.
The type being used at any particular time
is a function of size of fish being fed,
whether the fish are feeding at the surface
or in the water column, and if an antibiotic
is incorporated.

Catfish fry in hatcheries are fed finely
ground meal- or flour-type feeds
containing 45-50 percent protein.

 Fines or crumbles from 28 or 32 percent
protein feeds for food fish growout are
suitable for fry stocked in nursery ponds
until they reach 1-2 inches in length.
Larger fingerlings should be fed small
floating pellets (1/8 inch diameter)
containing 35 percent protein.

 Advanced fingerlings (5-6 inches) and
food fish are generally fed a floating feed
of approximately 5/32 - 3/16 inch in
diameter containing 28-32 percent protein.
Some producers switch to a slow-sinking
feed during the winter.
Antibiotics are administered to catfish
through incorporation in feeds. Depending
on the particular antibiotic chosen, the feed
may either be floating or sinking.

Feeding

Despite considerable research, feeding
catfish is far from an exact science. It is a
highly subjective process that differs
among catfish farmers.

 The variation in feeding practices is a
product of numerous factors such as
cropping system, fish size, ability to
manage water quality, experience of
feeding labor, and difficulty in estimating
fish inventory.
In general, fish should be fed once a day as
much feed as they will consume without
adversely affecting water quality.

 However, depending on water quality
variables and the health of the fish, it may
be advisable to restrict the daily feed
allowance or to feed less often. Long-term
feed allowance should not exceed 100-125
pounds per acre per day.

Most catfish producers feed once a day, 7
days a week during the warmer months.
Although feeding twice a day may slightly
improve growth of fingerlings, the logistics
of multiple feedings on large catfish farms
make it impractical.

Feed is typically blown onto the surface of
the water using mechanical feeders. Feeds
should be scattered over as wide an area as
possible to provide equal feeding
opportunities for as many fish as possible.
Feeding with prevailing winds allows the
feed to float across the pond and minimizes
the amount of feed washing ashore.

Overfeeding should be avoided since
wasted feed increases production costs.

CONSTRUCTION OF THE POND(mobile
for pond)


The lenght of the pound should not less
than 6ft for private consuptins

 while that of Commercial production
should be 12ft 300-700fish and above
pending on the amount of fish purchase.
Pond Construction
Proper design and construction of ponds is
critical to the success of a commercial
catfish operation.

Well-designed ponds, constructed on soil
with a proper clay content and adequate
water supply, have a useful life of at least
10 years.

Pond Types(Earth pond)


Three types of ponds are used in catfish
farming.

The first, called embankment or levee
ponds, is the most common type of pond
used in channel catfish farming.

 Embankment ponds are the preferred type
for large-scale catfish farming because
they can be built in large contiguous tracts,
which aids in pond management.

Embankment ponds are built on flat land
by removing soil from the area that will be
the pond bottom and using that soil to form
levees or embankments around the pond
perimeter.

The second type, watershed ponds, are built
in hilly areas by damming a small stream.
In the long term, the major source of water
is runoff from the drainage basin above the
dam, although a source of pumped water is
desirable to help offset evaporation and
seepage during droughts.

 Watershed ponds represent less than 10
percent of the total pond area devoted to
channel catfish farming, but are common
in some regions, such as western Alabama.
The third pond type is a hybrid between
embankment and watershed ponds.

 These ponds may have two or three sides
consisting of embankments (actually low
dams) across a relatively small drainage
basin.

 A significant amount of water may be
obtained from runoff, but because the
catchment area above the pond is relatively
small, a source of pumped water also must
be available. Hybrid watershed-
embankment ponds are built in regions
with gently rolling topography, such as the
Blackland Prairie of east Mississippi.
Pond Morphology
The ideal size and depth of catfish ponds
has changed in recent years. Fish farmers
report that smaller ponds (8 to 10 acres)
are easier to manage and feed than larger
ponds (18 to 25 acres). Research indicates
and producers confirm that deeper ponds
(5 to 6 feet average depth) have a longer
life expectancy and allow greater water
conservation. A bottom slope of 0.2 to 0.3
inches per 100 linear feet along the long
axis is recommended for adequate
drainage.
Interior levees should have a minimum top
width of 16 feet to allow vehicle access for
management purposes even in wet
conditions. Main access levees should have
a minimum top width of 20 feet (preferably
25 feet) to accommodate fixed equipment
such as wells, generators, and aerators
while permitting passage of feed delivery
and hauling trucks. These main levees
should be graveled for all-weather access.
Slope is expressed as the horizontal
distance (in feet) that results in a 1-foot
change in height. For most soils, an
outside levee slope of 3:1 is recommended.
Inside slope for commercial ponds typically
ranges from 3:1 to 4:1.
A single 10-inch diameter drain of heavy
gauge, coated metal or PVC pie is adequate
to maintain water level and drain a
commercial pond. The drain should extend
into the pond and past the outside levee toe
by at least 5 feet. A perimeter drainage
system should be constructed to receive
effluents and to prevent water from
standing outside levees.
Water Quality
Water supplies for catfish ponds are
usually of good initial quality. However,
once the water is used for culture, its
quality deteriorates. This deterioration of
environmental conditions is ultimately
traceable to the use of feed. Despite the use
of high quality feeds and careful feeding
practices, relatively little of the nutrient
value of feed is converted to catfish flesh.
The remaining nutrients derived from fish
wastes stimulate excessive phytoplankton
growth. High rates of phytoplankton
metabolism cause pronounced diurnal
fluctuations in dissolved oxygen
concentrations, dissolved carbon dioxide
concentrations, and pH. Such fluctuations
cause stress in fish resulting in reduced
fish growth rates, poor feed conversion,
and reduced resistance to disease. In
extreme instances, such as depletion of
dissolved oxygen, fish may be unable to
adapt and will die.
water aeratorLiterally hundreds of
environmental variables may affect fish
health and survival, but fortunately only a
few are important in commercial catfish
culture. Because their concentrations may
change rapidly, substances affected by
biological activity (dissolved oxygen,
carbon dioxide, ammonia, and nitrite) are
the most important aspects of water quality
and its management in catfish pond
aquaculture.
The development of environment-related
off-flavors is another important aspect of
water quality management. Off-flavor is
unlike the previously listed water quality
variables because it does not pose a direct
threat to fish health. Rather, it affects the
acceptability of fish for processing, which
causes delays in harvesting. As such, it
increases the cost of production and
exposes fish to additional risk of loss to
diseases or predators.
Important Water Quality Variables
Dissolved Oxygen: The supply of dissolved
oxygen often becomes limiting to catfish
because the combined respiration of fish,
phytoplankton, and mud-dwelling
organisms exerts a tremendous demand for
oxygen. At high phytoplankton biomass
levels (which is the typical condition in
catfish ponds during summer), oxygen
production by algae is insufficient to meet
the respiratory demand of the pond
community and a daily oxygen deficit
develops. If this deficit is not offset by
artificial aeration, dissolved oxygen levels
will drop very low and fish will die.
The key to successful management is early
identification of those ponds that may
require supplemental mechanical aeration
to keep fish alive. Aeration is initiated
when dissolved oxygen concentrations fall
to a level considered critical (usually
around 3 to 4 mg/L). Under current
production practices, nearly every catfish
pond has dissolved oxygen concentrations
less than 2 mg/L at dawn during mid-
summer. The duration of low dissolved
oxygen concentrations at night usually
ranges from 3 to 6 hours/day during mid-
summer. Aeration is continued until past
dawn when measurements indicate that
dissolved oxygen concentrations are
increasing as a result of photosynthetic
activity.
Carbon dioxide: High rates of respiration
in ponds with abundant plankton and high
densities of fish result in rapid loss of
dissolved oxygen and accumulation of
carbon dioxide over the nighttime hours
during summer months. Dissolved carbon
dioxide concentrations of 5 to 10 mg/L are
common on summer mornings in catfish
ponds and appear to be well tolerated by
channel catfish. They can survive in waters
containing up to at least 60 mg/L dissolved
carbon dioxide provided dissolved oxygen
concentrations are high. Higher
concentrations may cause death but
chronic problems are rare because daytime
uptake in photosynthesis normally serves to
remove all the carbon dioxide that is
produced in overnight respiration.
Ammonia: Ammonia is the major
nitrogenous waste product excreted by fish.
The fact that culture is possible at high
feeding rates indicates that transformations
and losses of nitrogen act to reduce
ammonia concentrations. Additionally, as
ammonia begins to accumulate, fish
respond with reduced appetite, leading to
lower rates of ammonia excretion and
reduced ammonia concentrations in the
water. As such, there are very few
documented cases of acute ammonia
intoxication in commercial channel catfish
ponds. However, ammonia levels can be
used to predict the onset of possible nitrite
accumulations.
Nitrite: Nitrite is an intermediate product
in nitrification, which is a common,
bacteria-mediated transformation of
ammonia to nitrate in soils and water.
Nitrite accumulates to significant levels in
ponds only when ammonia concentrations
are relatively high and some factor causes
the rate of ammonia oxidation to nitrite to
exceed the rate of nitrite oxidation to
nitrate. Accumulation of nitrite is
undesirable because it can be toxic to fish
at relatively low concentrations.
Nitrite toxicosis caused large losses of
catfish in the early days of the industry, but
losses are now very rare. An inexpensive
and convenient prophylactic treatment
using common salt has been developed and
monitoring programs are easy to
implement. As such, losses to nitrite
toxicosis will result only when the farm
manager is negligent in instituting the
proper management plan
Off-flavor
When channel catfish are fed a grain-
based diet and raised in clean water, they
have a characteristic mild flavor. Pond-
raised catfish may, however, develop
flavors that can be disagreeable. All catfish
processing plants sample fish for flavor
quality before processing as a quality
control measure. Fish are sampled several
times over the weeks before a projected
harvest date and if any of the samples have
undesirable flavors, the fish will not be
accepted for processing.
Most off-flavors in pond-raised catfish are
caused by odorous compounds absorbed by
fish from the water. Most off-flavors in
pond-raised catfish are caused by naturally
occurring organic compounds produced by
aquatic bacteria or algae. These
microorganisms synthesize and release
compounds into the water, where they are
absorbed through the gills, skin, or
gastrointestinal tract of fish.
Managing off-flavors can be divided into
two general approaches: purging the
compound by moving fish to a "clean"
environment or using algicides to kill
odorous aquatic bacteria or algae. Many
farmers choose a more passive approach,
however, and simply wait to harvest fish
when they are on-flavor. This approach
works to some degree because the
composition of pond phytoplankton
communities constantly changes. When
community composition changes and the
odor-producing species disappears, off-
flavors produced by aquatic bacteria or
algae will be purged from the flesh and
flavor will improve. However, it is
impossible to predict how long the odor-
producing microorganisms will remain in
the pond. They may disappear in a week or
may persist for months.
Production Process
A typical production cycle for channel
catfish farming begins with spawning of
brood fish. Spawning begins in the spring
when water temperatures increase to above
70º F. At that time, brood fish held in
ponds randomly mate and the fertilized
eggs are collected from spawning
containers and moved to a hatchery. Eggs
hatch after 5 to 8 days of incubation and
fry are reared in the hatchery for an
additional 4 to 10 days. Fry are then
transferred to a nursery pond, fed daily
through the summer, and harvested in
autumn or winter as fingerlings.
Fingerlings are then stocked into foodfish
growout ponds, fed daily, and harvested
when they reach 1 to 2 pounds. Roughly 18
to 36 months is required to produce a food-
sized channel catfish from an egg.
Foodfish are harvested year-around to
meet the needs of processing plants, so
ponds on a given farm usually contain fish
at various stages of growout throughout
the year.
Maintaining Brood stock
Aerial photo of catfish pondsChannel
catfish brood stock are easy to maintain in
pond culture, and spawning efficiency is
reasonably good without any special
manipulation of environmental conditions
or the need for hormone treatments.
Although channel catfish may mature at 2
years, they must be at least 3 years old and
weigh at least 3 pounds for reliable
spawning. Fish 4 to 6 years old, weighing
between 4 and 8 pounds are considered
prime spawners. Older fish produce fewer
eggs per body weight and larger fish may
have difficulty entering the containers
commonly used as nesting sites.
Brood stock are maintained at relatively
low standing crops (less than 2,000
pounds/acre) to provide good
environmental conditions and minimize
suppression of spawning by overcrowding.
Brood fish are seined from ponds and
inspected every year or two. Large fish,
which may be poor spawners, are culled
and replaced with smaller, younger brood
fish. Periodic inspection of brood fish also
provides an opportunity for adjusting the
sex ratios within brood populations.
Spawning activity will begin in the spring
when water temperatures are consistently
around 75º F. Spawning occurs over a
period of several hours as several layers of
adhesive eggs are deposited in spawning
containers. Females between 4 and 8
pounds typically lay between 3,000 and
4,000 eggs per pound body weight.
Spawning success (percentage of females
spawning) ranges from 30 to 80 percent
each year, and depends mainly on the
condition and age of the female brood fish
and water temperatures during the
spawning season.
Nesting containers are checked every 2 or 3
days for the presence of eggs. The eggs
collected from the brood pond are placed in
an insulated, aerated container and
transported to the hatchery.
Hatchery Phase
Hatcheries used to produce catfish fry are
simple facilities that use flow-through
tanks holding about 90 to 100 gallons of
water for egg incubation and fry rearing.
The most critical factor for a successful
hatchery is a dependable supply of high-
quality water.
Egg hatching tanks are equipped with a
series of paddles spaced along the length of
the tank to allow wire-mesh baskets to fit
between them. One or two egg masses are
placed in each basket and the paddles
gently rotate through the water to provide
water circulation and aeration. The
incubation time varies from 5 to 8 days
depending upon water temperature.
At hatching, the fry (called sac-fry at this
point) fall or swim through the wire-mesh
basket and school in tight groups. Sac-fry
are siphoned into a bucket and transferred
to a fry rearing tank. Aeration in fry
rearing tanks is provided by surface
agitators or by air bubbled through
airstones.
Initially, sac-fry are not fed because they
derive nourishment from the attached yolk
sac. Over a 3- to 5-day period after
hatching they absorb the yolk sac and turn
black. At that time fry (now called swim-up
fry) swim to the water surface seeking food.
Swim-up fry must be fed 6 to 12 times a day
for good survival and growth. Fry are fed
nutritionally complete feed for 2 to 7 days
before they are transferred to a nursery
pond.
Fingerling Production
Culture practices for fingerling production
are relatively standardized across the
industry, especially when compared to the
wide variety of production strategies used
to grow food-sized catfish. Fry grow faster
when stocked at lower densities but more
space is required to grow larger fingerlings
at lower densities. Stocking rate is
therefore a compromise between benefits of
producing large fingerlings for foodfish
growout and the economics of producing
more small fingerlings in less space. Fish
are fed a manufactured feed and grown to
fingerling size (3 to 8 inches long) over a 5
to 10 month period. Fish are either allowed
to continue growing in their original
nursery ponds or are harvested and
transferred to other ponds for growout to
stocker-sized fish of 0.1 to 0.25 pounds or
to food-sized fish of 1.2 to 2.5 pounds.
It is important to fertilize nursery ponds so
that they contain abundant natural foods to
promote growth until the fry are large
enough to switch to manufactured feeds. A
finely ground feed should be offered once
or twice daily to train fish to accept the
feed. As the fish grow, feed particle size is
increased. A month or so after stocking, the
fish (now called fingerlings) are fed once
or twice daily to satiation, using a small
floating pellet with 32 to 35 percent crude
protein.
Because fingerling populations are
particularly susceptible to infectious
diseases, disease management takes on
added importance in this stage of
production. Survival of catfish fry to
fingerlings varies greatly from pond-to-
pond depending on the initial condition of
the nursery pond, losses to bird predation,
and the incidence of infectious diseases.
Average survival from fry stocking to
fingerling harvest in excess of 60 percent
across all ponds on the farm is considered
to be very good.
Foodfish Production
Cultural practices used for foodfish
production differ from farm to farm, and
the process of growing a food-sized catfish
can take many paths after the fingerling
phase. Most farmers divide fish stocks only
once between the nursery phase and the
foodfish growout phase. In this scheme,
fingerlings are harvested and restocked
into foodfish ponds at roughly one-tenth to
one-twentieth the density of nursery ponds
because fish will be ten to twenty times
heavier when harvested as foodfish. This
one-step production scheme is not as
simple as it appears because there are
many options for managing foodfish
ponds.
Another approach to producing food-sized
fish is to divide twice between the nursery
phase and foodfish growout. The first
division produces a medium-sized fish
called a "stocker". The second division is
made when stockers are harvested and
restocked for growout to food size. In this
scheme, small fingerlings (2 to 3 inches)
are stocked at about 40,000 to 60,000
fish/acre and grown over one season to
produce stockers weighing 0.1 to over 0.3
pounds. The stockers are then harvested
and moved to foodfish growout ponds. As
with the one-step scheme described above,
there are several options for foodfish
growout using stocker-sized fish.
The three fundamental production
variables in foodfish growout are cropping
system, stocking rate, and size of
fingerlings to stock. Farmers use various
combinations of these variables and it is
impossible to describe a typical
management scheme for production of
food-sized channel catfish. Farmers have
developed and used various production
schemes based on experience, personal
preference, and perceived productivity and
profitability.
Cropping system refers to the stocking-
harvest-restocking schedule. In the single-
batch system, the goal is to have only one
year-class of fish in the pond at a given
time. Fingerlings are stocked, grown to the
desired harvest size, and all fish are
harvested before the pond is restocked with
new fingerlings to initiate the next
cropping cycle. In the multiple-batch
system, several different year-classes of fish
are present after the first year of
production. Initially, a single cohort of
fingerlings is stocked. The faster-growing
individuals are selectively harvested
("topped") using a large-mesh seine,
followed by addition ("under- stocking") of
fingerlings to replace the fish that are
removed plus any losses incurred during
growout. The process of selective harvest
and understocking continues for years
without draining the pond.
Whether ponds are operated as single-
batch systems or multiple-batch systems,
stocking rate is best defined as the
maximum fish density (number per acre)
over the production period. Under
commercial conditions, stocking rate
becomes an approximate goal rather than a
precisely managed population variable
because it is nearly impossible to know the
true inventory of fish in large commercial
ponds that are used for several years
without draining. There is no consensus on
the best stocking rate for commercial
production and rates used in the industry
range from less than 500 fish/acre to more
than 10,000 fish/acre. One explanation for
the wide range of stocking rates used by
catfish farmers is that production goals,
facilities, and resources vary from farm to
farm.
The size of fingerling to stock is a critical
factor in foodfish production, but very little
systematic research has been conducted to
determine the relationship between
fingerling size at stocking and economic
returns. Large fingerlings will reach
foodfish size faster than small fingerlings,
but large fingerlings are expensive because
they require more time and space to
produce. In addition, large fingerlings can
be difficult to obtain because most
fingerling producers prefer to stock fry at
relatively high densities and move
fingerlings to foodfish ponds as soon as
possible to avoid risk of loss to infectious
diseases and predacious birds. The best size
fingerling to stock is therefore a
compromise that depends on cropping
system, fish stocking density, and
fingerling availability.
Harvesting
Efficient harvesting of channel catfish
ponds is important to all phases of channel
catfish culture. The techniques currently
employed by the industry evolved primarily
from Great Lakes haul seine techniques.
There has been very little systematic
research conducted to improve on existing
techniques. Most of the innovations
implemented in harvesting fish during the
past twenty years have been the result of
trial-and-error by fish producers and
custom seining crews.
Photos of harvesting of
catfish.Preparation. Successful harvesting
operations require properly constructed
ponds. Levees should be wide enough to
accommodate large hauling trucks,
tractors, and fish loading equipment.
Gravel is imperative on main levees where
fish will be loaded onto hauling trucks. All
other levees should have a good ground
cover (or preferably gravel) to permit
seining in all types of weather.
To ensure the most efficient harvest
possible for any given pond, producers
must be certain that the production pond
contains an adequate amount of fish of
harvestable size. To minimize the expense
per pound of fish transported to the
processing plant, the transport truck needs
to be filled to or near capacity. Typically, a
producer marketing fish to a large
processor will not schedule a harvest until
20,000 to 25,000 pounds of graded fish will
be retained in the harvest net.
Prior to each food fish harvest, producers
must arrange for their fish to be placed on
the processing schedule. Producers must
first submit fish samples to processing
plants to check flavor quality. Once a
processor determines that a pond is "on-
flavor", the process of scheduling the
harvest can begin. There are many factors
that complicate scheduling including,
processing rights, proximity to plants,
availability of fish, and re-occurrence of
off-flavor.
Basic equipment. The basic requirements
are similar for fingerling and food fish
harvesting operations. Equipment
requirements consist of a commercial
harvest seine, a hydraulic seine reel, a flat-
bottomed aluminum boat outfitted with an
outboard motor and a seine catcher, two
tractors, and various live cars for holding
and grading fish. An additional tractor
equipped with a PTO-driven aerator is
recommended to keep water moving in any
area where fish are concentrated.
In order for a seine to operate properly, the
length of the seine should be 1.5 times the
widest section of the pond. This allows the
seine bottom to conform to the shape of the
pond bottom and minimizes the tension on
the mud-line. In general, the depth of the
seine should be 1.5 times the deepest
section of the pond. Most food-fish seines
are 9 foot deep for use in delta-style ponds,
but may be as much as 12 foot deep for use
in deeper watershed-style ponds. The vast
majority of fingerling seines in use on
commercial farms are 8 foot deep, but some
deeper, watershed style ponds require 10
foot deep seines.
Basic harvesting operation. While the
process of seining a pond is straight-
forward, a certain amount of skill and an
understanding of basic fish needs are
required to land fish successfully with a
minimum amount of stress. Even under
ideal conditions, a typical seine haul will
seldom catch more than two thirds of the
fish in a levee style pond.
Typically, at least five persons are required
to seine a commercial pond. Two persons
are required to drive tractors; one to pull
the hydraulic seine reel, and the other to
pull the other end of the seine. Two more
individuals are required to stand on the
mudline at the base of the levee as the seine
is pulled through the pond. The fifth
individual is required to operate the seining
boat and monitor the seine as it is pulled
through the water, watching for indications
that the seine is catching too much mud.
Once both ends of the seine are pulled
around the corners of the pond, the
tractors converge in the vicinity of where
the hauling truck will eventually be loaded.
This area should be clear of overhead
power lines and the pond bottom and water
depth should be suitable for containing the
fish in a net enclosure, grading, and
loading out. Often, producers choose to
land fish close to the aerator and the well
to help improve water quality in the area
where fish will be confined.
Technical Advances. Researchers at
Mississippi State University have developed
a novel design for catfish seines. The
original design for the seine was developed
in collaboration with the National Marine
Fisheries Service Lab in Pascagoula,
Mississippi. The seine design incorporates
braided polyethylene mesh, a modified mud
roller, a larger seine tunnel, and replaces
the frame mechanism used to mate the
seine to the live car with an industrial-
strength zipper system. The braided
polyethylene mesh is a good choice for
constructing seines and socks. The
modified mud roller design eliminates
much of the "mudding down" problems
associated with older muddy ponds. The
zipper system allows the sock to be attached
quicker and eliminates the potential for
twisting of the seine tunnel. More
importantly, it eliminates the "bottleneck"
effect of crowding fish through a tunnel
and frame, which can significantly reduce
the amount of time required to land fish in
live cars. A prototype seine was used to
harvest catfish from ponds ranging from 4
to 10 acres at the NWAC. Average catch
was 20 percent better than with
conventional seines and seining time was
reduced by 45 percent.
Grading
Most intensive catfish production
operations employ the sock grading method
of landing and grading fish. Typically, a
tunnel is sewn approximately 100 to 125
feet from the end of the harvest seine. An
open-topped net enclosure known as a live
car or sock is attached to the harvest seine
tunnel. The harvest seine is carefully
pulled toward the levee as fish pass
through the tunnel and into the sock.
Grading catfish with socks depends on
mesh size, time, water temperature, water
quality, and the general health of the fish.
Typically, to achieve the desired level of
grading, fish must be held in socks for a
minimum of four to six hours. It is
common for producers to hold fish
overnight in grading socks to encourage
removal of small fish. Socks must be staked
out properly in order to avoid fish escaping
and to encourage grading. A tractor PTO-
driven paddlewheel aerator should be
placed along the bank to gently pull
oxygenated water through the sock.
Technical Advances. An adjustable
horizontal bar grader for sorting channel
catfish has been developed by David Heikes
at the University of Arkansas at Pine Bluff
and has proven to be a valuable
management tool for fingerling production
on several commercial farms. A larger
version of the in-pond grader design is
currently under investigation and shows
promise for grading foodfish. Grading
foodfish with the in-pond grader involves
additional handling and labor, but allows a
producer to grade a crop of foodfish
immediately after seining. The grader can
grade 10,000 pounds of food-sized catfish
in 2 to 6 minutes. One series of tests
showed that 5 to 11 percent more weight of
sub-harvestable size fish can be graded
compared to current technology, resulting
in a 12.5 percent increase in average
weight of fish available for processing.
Once the fish have been graded with an in-
pond grader, inventory estimates can be
obtained from the holding sock. The use on
an in-pond grader may be particularly well
suited to grading fish in cold weather when
sock grading efficiency drops off.
Loading
Loading channel catfish from holding
socks onto transport tanks is typically
accomplished with a hydraulic loader
outfitted with a boom, lift net, and hanging
scale. Two of the most common types of
hydraulic loaders are a modified backhoe
and a reconditioned logging truck. A long
boom is attached to the hydraulic arm of
the loader to extend the basket to the live
car from the pond bank and lift the fish up
to the transport tank. The lift net is
suspended from a hanging scale attached
to the boom. The fish are weighed before
being released into the tank through the
trap door in the bottom of the lift net.
Transport
Channel catfish can withstand the rigors of
transport fairly well at all life stages.
However, proper procedures are critical
during transport of eggs, fry, and
fingerlings because damage or stress can
result in poor survival. Care should also be
taken when "live hauling" food-sized
catfish to specialty markets because they
are expected to remain alive for extended
periods until sold to the final consumer.
Food-sized catfish bound for processing
plants are transported at higher densities
because fish are held only briefly before
slaughter.
Disease
The "low-intensity" management practices
used prior to the 1980's generally resulted
in good pond water quality and lower
overall stress on fish populations. Lower
fish densities also meant less efficient
transmission of disease organisms. Over
the years, stocking and feeding rates
steadily increased and producers adopted a
multiple-batch cropping system wherein
new populations of fingerlings were
stocked into ponds with existing
populations of larger fish. These
production practices lead to the emergence
of infectious diseases as the primary
limiting factor in catfish production, and
disease outbreaks are not uncommon even
on well-run facilities.
A dead fish.About 45 percent of inventory
losses on catfish fingerling farms are
attributable to infectious diseases.
Corresponding survey data for food-sized
fish are lacking. Of the overall catfish
losses caused by infectious disease,
approximately 60 percent are the result of
single or mixed bacterial infections, 30
percent result from parasitic infestation, 9
percent from fungal infections, and 1
percent are of viral etiology. Multiple or
mixed infections often occur in pond raised
channel catfish making treatment decisions
difficult.
Economic losses resulting from infectious
diseases are difficult to quantify because
record keeping varies among farmers and
many diseases go unreported. Nevertheless,
infectious disease is believed to cost
producers many millions of dollars in
direct fish losses each year. In addition,
infectious diseases influence profitability
by increasing treatment costs, reducing
food consumption by fish, increasing feed
conversion ratios, and causing harvesting
delays. Fish-eating birds may also be
attracted to ponds with sick and dying fish
causing further losses.
There are several disease syndromes for
which the etiology remains in question,
such as channel catfish anemia (CCA),
which has also been referred to as "no
blood disease". Another syndrome is
visceral toxicosis of catfish (VTC), believed
to be caused by a toxin.
Once a disease outbreak occurs, effective
health management requires three basic
steps: problem identification, diagnosis,
and corrective management--all of which
must be performed in a timely manner to
avoid further losses. Whenever multiple
factors contribute to the disease process, it
makes the diagnosis more difficult and
often complicates corrective management.

				
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Description: THE BEST WAY OUT FOR COMMERCIAL CATFISH