General Information

1
Channel Catfish (Chapter 17)

• General Information
• Until relatively recently, channel catfish were
  not viewed favorable by the average consumer
• This species has now become the most important
  cultured species in in the USA
• In 2000, 50 of the commercial fish culture
  harvest was channel catfish
• 95 of this production occurs in 4 states
  Mississippi (70), Alabama, Arkansas, Louisiana
• Channel catfish is second only to largemouth bass
  as sports fish
• Topics
• Biology
• Commercial culture
• Culture facilities
• Production practices
• Water quality management
• Harvesting and processing
• The future of channel catfish farming

2
Channel Catfish

• Biology
• Order Siluriformes, family Ictaluridae (39
  species Canada to Central America)
• Channel catfish is native to central North
  America
• Slender and scale-less normally pigmented fish
  are white to silvery on the undersides shading to
  grayish blue or black on the back. Albinism is
  uncommon in the wild but is seen in domesticated
  strains
• Eight barbels, 4 dorsal and 4 ventral
• Soft-rayed fins, but spines on dorsal and
  pectoral fins
• Rounded anal fin contains 24-30 rays used to
  distinguish channel catfish from other species
  deeply forked tail fin in younger individuals but
  not so much as they grow older (see figure)
• Native habitat includes clear and flowing
  streams, sluggish rivers, lakes, and ponds
  bottom dweller, prefer sand and gravel
• Omnivorous
• Hardy fish (temp just above freezing to 34-35 C
  salinity 0-11 ppt)
• Sexual maturity achieved at 2-12 years may live
  up to 20 years and reach up to 20 kg in nature,
  2-4 years to achieve 0.5 Kg
• Spawning usually occurs in late spring.
  Temperature very important.
• Males select spawning site and attract females to
  breed, and chase them away after spawning males
  care for the egg masses until hatching (5-8 days)

3
Channel Catfish

• Commercial Culture
• Origins
• Channel catfish have always been a popular food
  fish in southeastern USA
• Regional popularity of this species stimulated
  interest in pond culture in the 1950s and 1960s
• Local markets remained the outlet for all
  production
• Expansion
• Rapid rate of expansion started about 1975
• In part due to declining profits from traditional
  agriculture (cotton, soybeans) and desire to
  diversify agriculture
• Establishment of large feed mills and fish
  processing plants also assisted in the expansion
  effort
• 1980 15,000 ha of ponds and 35,000 mt production
• 2000 80,000 ha of ponds and 270,000 mt
  production
• Favorable attributes of channel catfish
• Hardy fish broodstock relatively easy to spawn
• Grow-out stock do not spawn in culture ponds
• Do not require special feeds (commercial feeds
  available for all growth stages)

4
Channel Catfish

• Culture Facilities
• Over 98 of channel catfish in the USA are grown
  in earthen ponds because of lower production
  costs
• Two types of ponds are used
• Watershed ponds built in hilly areas by damming
  small streams disadvantage is that large groups
  of ponds cannot be set up (because of water
  quality problems) and large scale operations of
  scattered ponds makes management more difficult.
  This type of ponds used to some degree in
  Alabama.
• Embankment ponds built on flat land by digging
  a pond (1-2 m depth) and using the removed soil
  to form levees or embankments. Most common type
  of catfish pond (90). Pond size is compromise
  between ease of management and operation costs
  typically 4-8 ha per pond, rectangular in shape.
  Typically, source of pumped water is needed. See
  Fig. 17.2.

5
Channel Catfish

• Production Practices
• Spawning and breeding
• Production sequence begins with spawning of
  broodstock
• Spawning begins in spring when water temperatures
  reach gt 20 C (25-27 C seems optimal)
• Sexual maturity can be observed at 2-y-old fish
  weighing 0.3 kg. However, 3-y-old fish weighing
  1.5 Kg are needed for reliable spawning. Prime
  spawners 4-6-y-old fish at 2-4 Kg produce
  6500-9000 eggs (relative fecundity decreases with
  age beyond this age bracket)
• Broodstock that are held in ponds will spawn in
  spawning containers, such as buckets egg
  masses are then moved to the hatchery. Placement
  of the spawning containers can be used to control
  the timing of spawning. They are checked every 2
  or 3 days for the presence of eggs. See Figs.
  17.3-17.4
• Normally, there is no need for artificial
  induction of spawning (by hormone injections) and
  artificial fertilization, unless planned crosses
  are desired
• Brood fish are maintained at low standing crops
  (lt 2500 Kg fish/ha)
• Optimal sex ratios in brood ponds 2 males for 3
  females (see figure)
• Females only spawn once a year, but males can
  spawn 2-3 times
• At temperatures gt20 C, brood fish are fed daily
  1-2 of their body weight (prepared diet) at
  13-20 C, less feed every other day at lt13 C,
  they dont feed much

6
Channel Catfish

• Production Practices
• Spawning and breeding (continued)
• Before 1986, no planned breeding was conducted
  other than selection of broodstock for general
  performance traits
• In 1986, the USDA began research to improve the
  genetic potential of channel catfish. The first
  general release occurred in 2001 NWAC-103 line.
  This line has excellent growth compared with
  other strains available to the industry

7
Channel Catfish

• Production Practices
• Hatchery practices
• Channel catfish hatcheries are simple facilities
  that use single-pass, flow-through tanks for egg
  incubation and fry rearing
• Good water quality is required temperature may
  be most important single factor (Table 17.1)
• Shallow rectangular tanks are used for eggs and
  fry
• Eggs are placed in baskets along the length of
  the tank, which is equipped with a series of
  paddles attached to a shaft running the length of
  the tank to simulate the fanning of males
  guarding the nests. Incubation varies according
  to water temperature (5-8 days at 25-28 C). See
  figure
• At hatching, sac-fry fall through the mesh of the
  basket and congregate in the corners of the tank
• MacDonald jars are also used in some hatcheries
  after separation of eggs from the egg mass by
  treatment with sodium sulfite (see figure)
• Fry are transferred to similar tanks, but without
  the paddles. They are fed after they begin
  swimming (6-12 times daily)
• They are transferred to nursery ponds after 2-10
  days of feeding in the hatchery tanks

8
Channel Catfish

• Production Practices
• Nursery pond management
• Fry stocking density determines the average size
  of fingerlings after one season of growth
  (150-180 days). To produce 20 g fingerlings,
  stocking rate should be 200000-300000 fry/ha
• Nursery ponds should be fertilized (inorganic N
  and P) 3-4 weeks prior to stocking zooplankton
  will support fry for several weeks after stocking
• Fingerlings are then fed prepared diet 1-2 times
  daily to satiation about one month after stocking
• After 5-9 months fingerlings are harvested and
  transferred to grow-out ponds
• Size grading is usually necessary (by seine) to
  obtain a uniform population size for stocking
• Nursery ponds are drained and dried after harvest
  is completed

9
Channel Catfish

• Production Practices
• Grow out
• Management of grow out varies considerable from
  farm to farm
• Clean harvest system goal is to have only one
  year class of fish in the pond. Fingerlings are
  stocked, grown to a desired size (0.4-0.5 Kg) and
  completely harvested either all at once or over
  2-4 seinings over several months. This system
  still used by some farmers using watershed ponds
• Understocking system provides year-round supply
  of food size fish. Initially, a single cohort of
  fingerlings are stocked. The faster-growing fish
  are harvested using a large-mesh seine and new
  fingerlings are added to replace those taken out.
  This process continues for years without
  draining the pond. This is by far the most
  widely used system
• Advantages of clean-harvest system fish tend to
  be more uniform in size easier to maintain
  inventory (zeroed out after complete harvest)
  food conversion efficiencies tend to be better
  also, at least in theory, better disease
  management
• Advantages of understocking system fish of
  marketable size available for most of the year
  can manage to avoid off-flavor (more ponds to
  chose from) this is most important reason for
  this system being more commonly used than
  clean-harvest system.

10
Channel Catfish

• Water Quality Management
• Because of high stocking densities and feeding
  rates at catfish farms, large amounts of
  metabolic waste are generated. Since water is not
  replaced during the culture period, this waste
  can lead to environmental deterioration. Three
  factors are of primary concern
• Dissolved oxygen
• Ammonia and nitrite
• Off-flavors

11
Channel Catfish

• Water Quality Management
• Dissolved oxygen
• Phytoplankton metabolism is most important factor
  affecting DO in catfish ponds. Dense
  phytoplankton blooms can cause DO to fall to
  critical levels (3-4 mg/L) at night.
• Aeration is thus needed, usually starting at
  night and continuing during the daytime until
  levels have recovered.
• Metabolism is affected by temperature. Thus,
  fluctuations in DO levels are not as wide when
  temperatures cool down during the cool/cold
  season. At temperature lt15 C, problems of DO are
  uncommon.
• Paddlewheel aerators are most common device used

12
Channel Catfish

• Water Quality Management
• Ammonia and nitrite
• Ammonia excretion by fish is proportional to
  amount of feed consumed about 0.03 Kg of ammonia
  per Kg of feed consumed
• Ammonia accumulation is usually not a problem in
  catfish ponds
• However, nitrite has been known to occasionally
  accumulate in catfish ponds, especially in spring
  and fall when environmental conditions are
  rapidly changing.
• Nitrite combines with hemoglobin in blood to form
  methemoglobin and impairs oxygen transport and
  respiration (nitrite toxicosis)
• Nitrite toxicosis can be prevented by making sure
  that adequate levels of chloride (salinity) are
  present in water. Chloride competes with nitrite
  for intake by the gill. A ratio of 10mg/L of
  chloride for every 1 mg/L of nitrite-nitrogen is
  sufficient.

13
Channel Catfish

• Water Quality Management
• Off-flavors
• Off-favors can be caused by
• Feed ingredients
• Post-mortem rancidity
• Odorous compounds absorbed from the environment -
  this is the most common reason
• Geosmin and 2-methylisoborneol, odorous
  metabolites produced by certain blue-green algae
  (cyanobacteria), are most commonly responsible
  for off-favors in farm-raised channel catfish
• It is standard practice to taste-test fish
  before scheduling pond harvests
• Reasons for the occurrence of odor-producing
  cyanobacteria are not fully understood, and thus
  at the present time it is not possible to
  reliable manage catfish ponds to prevent
  off-flavors.
• Fish with off-flavors are simply left in the pond
  until the cyanobacteria disappear and the
  off-flavor goes away. Alternatively, fish may be
  moved to clean pond, but this process is labor
  intensive and stresses the fish.

14
Channel Catfish

• Harvesting and Processing
• Harvesting is usually accomplished using
  tractor-pulled seines with mesh sizes selected to
  capture the desired fish size normally, a square
  mesh size of about 4 cm is used to capture fish
  greater than about 0.4 Kg.
• See Figs. 17.5-17.7
• A variety of products are marketed fillets,
  nuggets, steaks, and whole dressed fish. About
  53 of the fish carcass can be processed into
  saleable product. Frozen fillets account for the
  largest portion of total sales (about 40).

15
Channel Catfish

• Future of Channel Catfish farming
• Channel catfish culture expanded at a remarkable
  rate from 1980 to 2000
• Future growth may be constrained by large capital
  investment needed to enter the industry and
  increasingly strict government regulations
  concerning environmental issues.
• Annual yields average about 4000 Kg/ha, which is
  half of what can be achieved under controlled,
  experimental conditions. Thus, technological
  improvements at the farm may be able to lead to
  higher yields.
• Better understanding and management of
  off-flavors, improved strains of fish and
  improvements in feeding practices may also help
  the industry