General Information Pacific salmon (several species within genus Oncorhynchus) and Atlantic salmon constitute the bulk of salmon production worldwide Pacific.

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

Salmonids(Chapter 15)

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)

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

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.”

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)

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

Salmonids

Prince Edward Island Aquaculture AlliancePrince Edward Island Aquaculture Alliance

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 (<50 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

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 don’t have to hold fish for another year

Smolts are transferred to marine farming facilities during their smoltification window in the spring

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 < 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

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

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

Salmonids