General Information

1
Salmonids (Chapter 15)

• General Information
• Pacific salmon (several species within genus
  Oncorhynchus) and Atlantic salmon constitute the
  bulk of salmon production worldwide
• Pacific salmon mostly capture fisheries
• Atlantic salmon mostly aquaculture (Tables
  15.1, 15.2, 15.3)
• Norway and Chile are top aquaculture producers
  (Table 15.4)
• Topics
• Biology
• Freshwater farming
• Marine Farming

2
Salmonids

• Biology
• The geographic range of salmonid distribution
  covers freshwater and marine coastal regions of
  the northern hemisphere temperate zone (scan 1)
• Life history of salmonids (Fig. 15.1)
• Comparison of several species (Table from Schreck
  et al 1995)

3
Salmonids

• Freshwater Farming
• Factors that must be considered
• Water flow and volume available
• Water quality (including temperature)
• Existence of other upstream farms
• Upstream land uses
• Other
• Farmers may specialize in
• Production and sale of eggs
• Production and sale of fry
• Production and sale of table fish

4
Salmonids

• Freshwater Farming (continued)
• Hatchery
• Water quality control is critical in salmon
  hatcheries. Heavy metals, suspended solids and
  low DO levels must be absolutely avoided
• Cadmium, copper, lead, zinc are very toxic to
  salmon eggs toxicity is reduced in water with
  high levels of hardness (lime may be added)
• Suspended solids can accumulate rapidly in
  salmonid egg incubators and can smother them
  filtration of influent water may be necessary
• Influent water must have oxygen levels at
  saturation and levels must not be allowed to drop
  below 6 mg/L.
• BOD increased during hatch due to the release of
  waste fluid from the hatched eggs and the empty
  egg shells.

5
Salmonids

• Freshwater Farming (continued)
• Spawning (focus is Atlantic salmon)
• Seawater fish acclimated to freshwater for
  several months
• Males and females may or may not be kept
  separately, but they need to be at conditions of
  low densities and high water quality
• Typically fish will mature asynchronously, and
  hormone preparations are necessary to synchronize
  maturation and ovulation
• Eggs are artificially fertilized after collection
  of gametes by hand stripping (after anesthesia)
  (Fig. 15.3)
• In Atlantic salmon, 1200-1500 eggs/kg can be
  collected from females weighing 4-14 kg.
• Fish are dried with a towel before collection of
  gametes to prevent water contamination and
  premature activation of sperm (water contact
  activates sperm)
• Eggs and sperm are mixed in a bowl or a bucket,
  mixed, and allowed to stand for 2-3 min
• Eggs are then gently washed with water and
  allowed to stand for 45-60 min to water harden
  (eggs increase in size and become hard to the
  touch)

6
Salmonids

• Freshwater Farming (continued)
• Egg incubators
• Upwellers (vertical cylinders) require minimal
  floor space and can hold large volumes of eggs
  preferred when production objective is eyed
  eggs for sale (pre-eyed eggs should not be
  handled)
• Trays (Heath system) can be stacked in banks of
  up to 20 per unit and are also space efficient
  1 L of eggs forming two layers in each tray (Fig.
  15.4)
• Eggs baskets within troughs are another method
• Concerns during incubation include
• Fungal infections (Saprolegnia) that spread from
  dead to live eggs. Usually control by short term
  treatment with malachite green (2 mg/L for 1 h).
  Other treatment include hydrogen peroxide or
  formalin
• Water flow necessary to maintain water quality
• Light egg incubators are covered or kept under
  dim light conditions to prevent exposure to
  bright light
• Temperature can affect developmental rates and
  health

7
Salmonids

• Freshwater Farming (continued)
• Alevins and fry at first feeding
• Alevins are also stressed by bright light and
  like the eggs, they are kept in dark conditions
  (lt50 lux at water surface)
• Suitable substrate must be provided to maintain
  alevin quietly and undisturbed so that they can
  achieve adequate development (Fig. 15.5)
• Atlantic salmon alevin begin exogenous feeding
  when they reach a weight of about 0.2 g.
  Exogenous (artificial diet) feeding should start
  prior to full resorption of the yolk sac
• First feeding may be done in troughs or tanks
• Fry may be graded at 4-5 weeks after first
  feeding to optimize growth efficiency and provide
  marketable fish throughout year
• In trout farming (e.g., rainbow trout), the
  farmer will continue to grow out the fish until
  market size in tanks or raceways (sometimes
  ponds)
• In salmon farming, the farmer will want to
  produce smolts for culture in marine environments

8
Salmonids

• Freshwater Farming (continued)
• Smoltification
• Transformation of freshwater parr to individual
  capable of migrating and adapting to marine
  environments
• Accompanied by behavioral, physiological and
  morphological changes
• Atlantic salmon parr must reach a minimum size by
  the start of the first winter to successfully
  undergo smoltification in the spring
• A bimodal distribution of growth is normally
  observed in hatcheries, the upper mode completing
  smoltification in the first spring (S1) and the
  lower, in the second spring (S2)
• The S1 fish have a size range of 10-15 cm at the
  start of the first winter, the S2 fish will be
  much larger at the start of the second winter
  prior to their spring-2 smoltification
• The objective of Atlantic salmon hatcheries is to
  produce as many S1 as possible individuals so
  that they dont have to hold fish for another
  year
• Smolts are transferred to marine farming
  facilities during their smoltification window in
  the spring

9
Salmonids

• Marine Farming
• The method of choice for marine farming of
  Atlantic salmon is cage culture
• Culture site characteristics
• Mostly inshore waters of high salinity (32-35
  ppt)
• Adequate depth to allow at least 5 m beneath the
  net
• Moderate current flow with good exchange of water
  to flush nutrients out
• DO greater than 80 saturation
• Temperature lt 18 C
• Site rotation should be practiced to minimize
  souring of the site. Recovery may take 6
  months to several years
• Cages may be set individually or linked together
  into platforms with service walkways
• Size of cages varies greatly 1-2 metric ton
  units to 100-150 metric ton units
• Net bags are usually 5-20 m in depth, and their
  shape is maintained by metal rings, weights ,
  etc. (Figs. 15.7, 2.7)
• Biofouling increased drag, weight and also BOD
  and requires nets to be removed and replaced for
  cleaning (more often in summer than in winter)
• Predation can be a problem e.g.,
• Seals can cut holes through the mesh or jump over
  the handrails they even are known to have
  attacked hatchery farmers
• Birds (cormorants, seagulls) can also take fish
  or mess the net
• Sharks, eels and other fish also prey on farmed
  salmon

10
Salmonids

• Maturation
• Male salmon may begin to develop their gonads
  before harvest time (jacks)
• Fish growth and flesh quality may be negatively
  impacted by maturation, and mortality rates are
  higher.
• Techniques to prevent maturation include
• The production of all-female stock by
  sex-reversal
• The production of triploid individuals by heat or
  hydrostatic pressure shocks

11
Salmonids

• Salmon Products
• Fresh fish
• Whole head-on, gilled and gutted fish (HOGG)
• Fresh fillets and cutlets
• Frozen HOGG
• Smoked side or portions
• Gravadlax
• Caviar, etc.
• All high value products