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An overview of Atlantic salmon, its natural history, aquaculture, and genetic engineering

Section 1:  Introduction - Salmon

Section 2: Fish Consumption in the United States

Section 3: Aquaculture

Section 4: Genetic Engineering of Animals

Section 5: FDA's Regulation of Genetically Engineered Animals


Selected Salmon Web Resources




Aqua Bounty Technologies, Inc., has submitted an application to FDA (the agency, or “we”) for approval of the “AquAdvantage” genetically engineered (GE) salmon. The agency will be holding two public meetings on this topic. The first will address the science-based questions that are the subject of the actual approval; the second will be to obtain comments from the public on how FDA should apply its food labeling framework to foods made from this specific genetically engineered animal. These two meetings are described in detail at http://www.fda.gov/AdvisoryCommittees/CommitteesMeetingMaterials/ VeterinaryMedicineAdvisoryCommittee/ucm201810.htm.

This document is intended to provide some basic information on Atlantic salmon, its consumption, and its aquaculture. It also describes the approach that FDA uses to regulate GE animals, including GE fish. The overview is presented in a question and answer format. We have also provided a list of selected salmon web resources, and a bibliography in case readers wish to follow up on any particular topic in more depth.

Section 1: Salmon

What are "salmon"?

Atlantic Salmon

Image 1: Illustration of Atlantic Salmon(Salmo salar).

Courtesy: N.O.A.A.

Salmon are fish that belong to the family of Salmonidae (biologists classify types of organisms according to similar characteristics: the term “families” encompasses the more commonly used terms “genus” and “species.” Within the Salmonidae family are the genus Salmo, which contains Atlantic salmon, and the genus Oncorhynchus, which contains Pacific salmon released into the Great Lakes, trout, and char. A common characteristic of salmonids is the presence of an adipose fin just in front of the tail on the dorsal (top) side. In general, these are all bony fish that are caught commercially from the wild, a dietary mainstay of aboriginal populations, sought after by recreational anglers, and farmed intensively because of their desirable taste and nutritional characteristics.
Atlantic salmon, Salmo salar (salmon, the leaper) is native to the North Atlantic, and is generally recognized to consist of three populations: North American, European, and Baltic.
Atlantic salmon change their appearance during their life cycles, but in general have an elongated shape and silvery color. As adults at sea, which is how we often think of schools of salmon, they have small scales, with silvery flanks and a white belly. As adults become sexually mature and migrate to fresh water, their color changes, becoming greenish or brown, and red or orange mottled. The males develop an exaggeratedly hooked lower jaw, and a staggered line of teeth.
Close-up of the head of a salmon

Image 2: Salmon undergo significant physical transformations in response to their environment

Courtesy: www.photos.com

Pacific salmon include a number of species, among them the well known and largest of the Pacific salmon, the Chinook (Oncorhynchus tshawystscha), sometimes referred to as “King,” “Blackmouth,” or “Spring” salmon. Coho salmon (Oncorhynchus kisutch) are found off the coast of Alaska and British Columbia, but their range spans the east and west borders of the North Pacific Ocean, as well as introduction into the Great Lakes. Sockeye (Oncorhynchus nerka) (or red) salmon, thought by many to be among the most flavorful of the Pacific salmon, has a very firm, orange-red flesh, and is caught commercially in Bristol Bay, Alaska, although its range extends almost as far as the Coho. Pink salmon (Oncorhynchus gorbuscha), are the smallest of the Pacific salmon, and are often referred to as “humpies” due to the bowed backs of the adults. Cherry salmon (Oncorhynchus masu or O. masou), or seema, have a fairly narrow range, and are found in the Western Pacific waters off Japan, Korea, and some parts of Taiwan. They are intensively raised in aquaculture and serve as a major food fish in the Far East. Chum (Dog, Keta, or Calico) salmon (Oncorhynchus keta) have the widest range of the Pacific salmon species, living as far south as the Sacramento River in California, as far as the Sea of Japan and the Lena River in Siberia.

How is Atlantic Salmon different from other “salmon”?

adult Atlantic salmon

Image 3: An adult Atlantic salmon

Courtesy: N.O.A.A.

Animals that belong to different genera or species generally have specific traits associated with those “memberships,” and so fish referred to as “salmon” that are from different species may be quite dissimilar. In addition to the fact that they are native to different oceans, Atlantic salmon (Salmo salar) differs from the Pacific salmon (Onchorynchus sp.) in many ways including habitat, appearance, ability to survive in particular geographical conditions, taste, etc.
One of the key biological differences between Salmo and Onchorynchus is that Atlantic salmon (Salmo) are iteroparous, that is, they do not die after returning to spawn in their streams in which they hatch, and can return to the sea (see discussion below on Atlantic Salmon Life Cycle). Pacific salmon, and other members of the Onchorynchus genus, on the other hand, are referred to as being semelparous, with mature members of the population generally dying within a few days or weeks of spawning.

How do Atlantic salmon live and reproduce?

Atlantic salmon have a complex life cycle, much of which is common to the Salmonidae family. One of the notable characteristics of salmon is that they are anadramous—that is, part of their lives are spent in fresh water, and part can be spent in salt water. Atlantic salmon have evolved finely tuned “chemotactic” systems (systems in the animal that allow it to recognize certain “chemical signatures”) that allow them to return to the very stream in which they were hatched to spawn after spending as many as five winters at sea, thousands of miles away. How they do this is still unknown, even though the life history of the Atlantic salmon was first described in 1527 at a Scottish university (Aberdeen).
Salmon migrating upstream to spawn

Image 4: Salmon migrating upstream to spawn

Courtesy: www.photos.com

In general, salmon eggs (roe) are laid by mature female fish (sometimes referred to as “hens”) after they have selected a quiet gravelly spot in a stream or pond in late fall (October or November). If the female accepts the courtship of a mature male, she begins a vigorous “dance” in which she uses her caudal fin (tail), swishing it back and forth vigorously to get the water to move the gravel at the stream bed to make a hollow (often referred to as a redd). She then proceeds to lay her orange-red roe (eggs) in the redd; the male aligns himself next to her and releases his milt (sperm) next to the newly released eggs.
Fertilization occurs as the eggs and milt intermingle. The female then buries the eggs in the gravel, and rests. The male continues to guard the female, and to drive away competitors aggressively until she has completed making redds and depositing her eggs. This may take as long as a week, and require the building of up to seven redds to deposit her nearly 7,500 eggs. At the end of this time, both male and female are exhausted; they generally swim back downstream to a pool where they rest and recover before beginning a new migration to the ocean a few weeks later. These post-spawn salmon are sometimes referred to as “kelts.” Many do not survive the first mating; some survive to mate twice, but very few mature males or females salmon survive to spawn three or more times.
Of all the fertilized eggs (sometimes referred to as “eyed eggs”) in the redds, only about 9-20% survive to develop over the winter, and, depending on temperature and water conditions, will usually hatch in April. The hatchlings, often referred to as “alevin,” are mostly transparent, and have large yolk sacs. They remain buried in their redds for another few weeks, feeding off their yolk sacs.
A. salmon eggsB. salmon alevin
Image 5: Salmon alevin hatch from eggs. (A) Fertilized salmon eggs in different stages of development. Notice the ‘eyed-eggs’ in top-center and top-left. (B) Salmon alevin hatch and rely upon their yolk sac for nourishment. Both images courtesy of www.wikipedia.org
Again, depending on conditions, usually by mid-May the yolk sacs are largely depleted, and the alevin leave their gravel beds to “swim up” that is, to take the critical gulp of air that fills their swim bladders. Once full, the air-filled swim bladder gives the still very small fish the buoyancy they need to maintain a position in the water. Once “swim up” has occurred, these small fish are referred to as fry (as in “small fry”). Hungry, they swim freely, and begin to eat—insect larvae, other small organisms called zooplankton, and fish eggs, including those of their own species.
As the fry mature, and become more fish-like in appearance, they develop small red spots along their sides, from which dark vertical stripes descend. These markings aid in camouflaging the young fish, which are preyed upon by other fish, as well as mammals and birds that live along rivers and streams. At this stage, they are referred to as “parr.” They remain in their natal (birth) streams, feeding on the larvae of insects, worms, and shellfish, and sometimes each other or related species (such as trout).
If there is plenty of food, and other environmental conditions are good (the water is clean and there is enough oxygen), parr grow rapidly during their first summers—that is, if they don’t get eaten by other fish, birds, or other animals that prey on parr. Parr can be very territorial, and aggressively protect their space from other parr. As the parr become larger, their territories expand, probably to ensure a reliable source of food.
Parr may spend between one and six years (usually two to three years) in their natal streams; at some point, if they are not in land-locked lakes, they begin their downstream migration and prepare for life in the sea. They are usually about six inches long at this point in their development (http://www.mass.gov/dfwele/dfw/fisheries/anadromous/salmon_life_cycle.htm).
salmon before and after smoltification

Image 6: Salmon smolt transition from life in fresh water (rivers and streams) to life in salt water (open oceans). The top panel depicts a salmon fry prior to smoltification. The bottom panel shows a fry that has undergone smoltification and can live in salt water.

Courtesy: N.O.A.A.

This involves changing their bodies’ physiology to adapt to salt water conditions, and is referred to as “smoltification” (the young fish that migrate to the sea are called “smolts”). In general, smolts tend to live for a while in brackish (part salt) water, such as bays and estuaries while they complete their adaptation to salt water. It is thought that the “imprinting” of the natal river occurs during smoltification (nmfs.nooa.gov/fishwatch). At this stage, they are silver in color, more elongated than the parr, and have darker fins.
At the end of the spring during which they have adapted to living in salt water, the smolt generally swim to sea. For example, Atlantic salmon leave Maine rivers some time in April or May, and can be found in the waters off Labrador and Newfoundland by mid-summer. They then migrate to take advantage of available food supplies and generally spend their first winter at sea off the coast of Greenland. While at sea, salmon are sometimes referred to as “opportunistic pelagic feeders.” That means they eat whatever is edible in the open sea: other fin fish, shell fish (including shrimp, krill, and other crustaceans), and zooplankton. In fact, it is the pigments in these organisms (crustaceans and zooplankton) that are in large part responsible for the orange-pink hue of most salmon. Salmon that do not eat crustaceans with pigment, especially those salmon that tend to spend their lives in freshwater lakes, tend to have a whiter flesh, which is considered a delicacy by some. 
As they mature, Atlantic salmon feed on finfish such as Atlantic herring, alewives, rainbow smelt, young cod, sand lances, flatfish, and small Atlantic mackerel. Atlantic salmon must also avoid being eaten themselves, as they are preyed on by marine birds, seals, and larger fish. After two years at sea, an adult salmon can weigh about 8-15 pounds, and be up to 30 inches long.
migratory pattern of the Atlantic salmon

Image 7: Atlantic Salmon demonstrate an expansive migratory pattern over their life cycle.

Courtesy: N.O.A.A.

During their time in the open sea, which can last from one to several winters, the fish become sexually mature. Upon first entering the sea, the salmon keep the silver hue and darker fins of the smolts, and gain some black spots on their backs. Their bodies become even more elongated, and they become strong and elegant swimmers.
Post-smolt salmon age is counted in units of “winters at sea.” In general, a salmon that spends one winter at sea prior to becoming sexually mature and returning to its natal stream to spawn is called a “grilse.” A salmon that spends two years at sea is referred to as a “2SW” (sea winter) fish. In general, the longer a salmon spends at sea feeding, the larger it becomes, although Atlantic salmon rarely get bigger than about 25 pounds.
Regardless of their age, as Atlantic salmon migrate back to their natal rivers and streams, the fish become sexually mature, and their shape and coloration begin to change, with pigment changes more prominent in the males. In general, males become redder on their bellies, or red with purple spots; females tend to be blue-black in color. They become less elongated and thicker in the body, the females, in particular, become swollen with eggs. The males also develop teeth and an exaggerated hooked lower jaw referred to as a “kype.” These are useful in fending off the unwanted attentions of other males to their selected females during spawning.
As previously mentioned, some salmon never make the transition to salt water environments because they spend their entire lives in landlocked lakes. In addition, a small percentage of the males become sexually mature in fresh-water as parr and are referred to as “precocious males.” Rather than migrating to sea, these small, young males establish residence in the still water in which mature salmon spawn. When the females release their eggs, the precocious males dart in and deposit their milt before the sexually mature large males can. Because they are small, the precocious males are not recognized as threats by the larger mature males, and are generally not the object of their aggression. Precocious parr make up approximately 1% of the male population, but may end up fertilizing up to 20% of the total eggs that are released by females.

What is the current status of wild Atlantic salmon populations?

The historical range of the North American Atlantic salmon (fish found in Canadian and U.S. waters) ranged from northern Quebec to Newfoundland, and southwest all the way to Long Island Sound. In colonial times, they could be found in almost every river north of the Hudson. Beginning in the 19th century, these populations began to decline precipitously. In the 1800s, Atlantic salmon became extinct in the Connecticut (CT), Merrimack (MA), and Androscoggin (NH, ME), rivers mostly likely due to the results of dam building to harness the energy of the water. These dams blocked access of the fish to their natal streams (and thus their spawning areas). Industrial pollution, from paper mills and textile factories, also contributed to the decrease in populations, as did commercial overfishing and climate changes that affect the temperature of the water in the ocean at the depths at which Atlantic salmon are found (2-10 meters below the surface). (Atlantic salmon need clear, sediment-free water and cold temperatures to survive). As an example, “weirs” (structures in rivers or estuaries that let water through while either directing fish to nets to be caught, or directly trapping fish) in Maine were reported as catching 90 metric tons of Atlantic salmon in the late 1800s and half that in the early 1900s.
Photograph from Bucksport, Maine (1891) depicting a weir erected to capture Atlantic salmon

Photograph from Bucksport, Maine (1891) depicting a weir erected to capture Atlantic salmon

Courtesy: N.O.A.A.

Today, very few rivers in Maine support wild Atlantic salmon. In fact, Atlantic salmon are extinct in 84 per cent of the rivers in New England that historically supported salmon. They are in “critical condition” in the remaining 16 percent. In 2004, only 60-113 individual fish were counted in the eight rivers in Maine that support Atlantic salmon. In 2000, the National Oceanic and Atmospheric Services’ (NOAAS) Fisheries Services and the U.S. Fish and Wildlife Service (USFWS) listed the Gulf of Maine Distinct Population Segment of Atlantic salmon as endangered under the Endangered Species Act. That designation was extended in 2009 to include fish in several rivers in Maine. Populations in Canada have also declined. In the 1970s, approximately 1.5 million salmon returned to their natal rivers in Eastern Canada; by 2004, that number had dropped to approximately 350,000 (http://www.traffic.orgdisclaimer icon).
The Northeast Fishery Management council developed a Fishery Management Plan for Atlantic Salmon in 1988. This authority extends over all Atlantic salmon of U.S. origin, and prohibits “possession” of Atlantic salmon, either as the intended catch of commercial fishing, or as the indirect (by catch) result of fishing for other fish. Commercial fishing of wild Atlantic salmon is now prohibited in U.S. federal waters, although recreational fishing is allowed. (Commercial fishing of wild Atlantic salmon still occurs off the coast of Greenland, where adult Atlantic salmon feed).


There is now a Recovery Plan for the Gulf of Maine Population Segment of Atlantic salmon, which identifies steps that need to be taken to stop the decline of the population (http://www.nero.noaa.gov/nero/hotnews/salmon/FinalATSRPlan.pdf). In addition, the United States is a member of the North Atlantic Salmon Conservation Organization (www.nasco.intdisclaimer icon), a group dedicated to the conservation, restoration and management of Atlantic salmon.

Section 2: Fish Consumption in the United States


How much salmon do Americans eat?

Fish consumption is on the increase around the world. According to the National Marine Fisheries Services, the amount of commercially caught fish (fin- and shell-fish), measured as “edible meat” consumed per person in the United States, increased from 11.2 lbs (~5.08 kg) in 1910 to 16.6 lbs (~7.53 kg) in 2004. Salmon consumption in the United States increased nine-fold between 1987 and 1999; during that time total European salmon consumption increased more than four times. Between 1992 and 2002, salmon consumption in Japan doubled. There are many reasons for this increase, including competitive pricing, the perception that eating fatty fish is healthy, and a general increase in fish consumption. Atlantic salmon is a good source of protein, with almost 20 grams per 100 gram serving, and is an excellent source of omega-3-fatty acids, which are thought to aid in cardiovascular health.


‘lox,’ or salt-cured (and often smoked) Atlantic salmon fillets.

Image 9: Photograph depicting ‘lox,’ or salt-cured (and often smoked) Atlantic salmon fillets. Lox is an example of how Atlantic salmon meat is used in many diverse culinary ways and is important to many different cultures.

Courtesy: www.flickr.com

Based on information available in the National Health and Nutrition Examination Survey (NHANES), a survey of food consumption in the United States conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention, among people who eat fish, those who are “big fish eaters” (they eat more fish than 95% of other fish eaters) consume, on average, about 300 grams per day (about 3 servings). Although tuna makes up a large proportion of that total fish consumption, if all the non-tuna fin fish eaten by people who eat a lot of fish were salmon, it would be around 200 grams per person per day. (NHANES 2003; Knapp et al. 2007.) 
How much of that fish is actually Atlantic salmon? That’s a difficult question to answer precisely, because it’s hard to keep track of what kind of salmon an individual person eats, and not all stores or restaurants that sell salmon tell consumers what kind of salmon it is. The National Marine Fisheries Service estimates that salmon makes up 14% of the total U.S. fish consumption; in 2004, annual total Atlantic salmon consumption across the entire U.S. averaged 284,000 metric tons (a metric ton is 1,000 kg, or 2,200 pounds). Of that, 180,000 metric tons were Atlantic salmon. And because commercial catches of Atlantic salmon are prohibited in U.S. waters, almost all of the Atlantic salmon sold in the United States is either wild caught in Europe, or farmed fish. Recent estimates are that about two-thirds of the salmon that we eat in the United States is farmed, and 94% of the Atlantic salmon that we eat is imported (farmed and wild caught) (Knapp 2007), coming mainly from Chile, Norway, Scotland, and Canada.
In 1989, salmon made up about 5% of all the fish we ate; by 2004, that amount almost tripled to 13%. Salmon ranks third among all the fish we eat in the United States after shrimp (25% of total fish eaten in the United States) and canned tuna (20% of total fish eaten in the United States) (all estimates from Knapp 2007). Compared with meat from land animals, though, the amount of fish we eat is quite low (See Figure 1).


Figure 1: Annual Per Person Consumption
of Meat and Fish in the United States
(adapted from NMFS)
Beef…………….....…….63 pounds
Poultry……………....….73 pounds
Pork, lamb, veal……..49 pounds
All fish…………....……~16  pounds

If we compare total salmon consumption to total “muscle tissue,” it’s about one percent of the total. Averaged over all Americans, the 200 g/person/day figure mentioned two paragraphs ago probably represents individuals who may not eat a lot of other meat. If they were to consume that amount of salmon every day for a year, their annual consumption would be about 160 pounds of salmon per year.

In 2006, the Food and Agriculture Organization (FAO) of the United Nations issued a report that predicted that there will be a 25% increase in global demand for seafood by 2030. They based this estimate on the current rate of increase in consumption of fish, and a 2030 world population of 8 billion (we are currently at about 6 billion people). Given the current decline and depletion of many stocks of wild fish, the FAO estimate that the increase in demand from fish can only be met by aquaculture, which accounted for about one-third of the fish caught annually at the time the report was prepared. More recent studies indicate that half the fish eaten around the world today is farmed (Naylor et al. 2009).

Section 3: Aquaculture


What is Aquaculture?

Unlike commercial fishing, which is the harvesting of wild fish, aquaculture is raising fish for harvest under controlled conditions. Aquaculture is an ancient practice; there is evidence that eels were raised by aboriginal people in Australia as early as 6000 BC. A series of channels and dams were built in a flood plain to contain eels; the fish were captured in woven traps, smoked, and eaten year round. The Chinese also began to use aquaculture a long time ago; around 2500 BC, carp were raised in lakes in China. Early Christian monasteries in Europe adopted the Roman practice of raising fish in ponds. Those approaches were used until the development of hatcheries in the eighteenth and nineteenth century, when native wild fish such as trout and salmon began to experience declining populations. In the United States, brook trout were being hatched and raised in upstate New York as early as 1859; by 1866, artificial fish hatcheries had been established in the United States and Canada, as the techniques of artificial fertilization and the subsequent hatching of eggs began to be developed. Their techniques were soon widely used throughout North America and Europe.
Commercial salmon farming began to be established in the 1970s, at about the same time that restrictions establishing the 200 mile limit fishing zones were put into place. Japan was one of the first countries to develop hatchery programs and extend those programs to full aquaculture. By the late 1990s, hatchery-based salmon harvests made up about 80 percent of Japan’s total salmon production.
Aquaculture has become one of the primary sources of fish in the United States and around the world (See Figure 2). The Food and Agriculture Organization of the United Nations has estimated that aquaculture has grown by about 8% per year over the past thirty years; at the same time, catches from the wild have either remained constant or dropped due to diminishing fish stocks. China is the world’s largest producer of fish from aquaculture, with over 30 million metric tons of fish coming from fish farms. Norway and the United States are numbers nine and ten respectively, with 0.64 and 0.61 metric tons of fish produced from aquaculture.


Figure 2: Fish Production from Aquaculture in 2004
(adapted from FAO)
Total production of fish from aquaculture….45,500,000 metric tons
32% of the total world wide fish production (wild plus farmed)

Although salmon aquaculture is thought to have grown out of the Danish system of raising rainbow trout in freshwater during the 1890s, it wasn’t until the 1960s that the Norwegians were able to successfully grow salmon in net pens in the protected salt waters off the coast of Norway. By 1972, five aquaculture facilities produced about 46 metric tons of Atlantic salmon—that amount grew to 173 farms producing 4,300 metric tons of salmon by 1980. In the years after that, growth in Atlantic salmon aquaculture moved to other locations, and today Atlantic salmon are being raised in net pen aquaculture in Scotland, Ireland, Canada, Chile, the United States, Australia, New Zealand, and the Faroe Islands.

The first harvest of Atlantic salmon grown under commercial conditions in the United States yielded six metric tons of fish (~13,230 pounds) in the late 1970s. The Atlantic salmon aquaculture industry has grown considerably since then, with FAO estimating that current worldwide production of farmed Atlantic salmon exceeds 1 million metric tons. Approximately 90 per cent of the farmed salmon market is made up of Atlantic salmon, and over half of the total world salmon market is farmed Atlantic salmon. http://www.fao.org/fishery/culturedspecies/Salmo_salar/en.disclaimer icon 
Norway is the largest producer of farmed Atlantic salmon today. Norwegian waters are well-suited to net pen farming. The deep, sheltered sites off the Norwegian coast have temperatures and salt concentrations that are well suited for the growth of Atlantic salmon, and Norwegian fish farmers have selectively bred strains of Atlantic salmon that grow well under farmed conditions. Most strains of commercially farmed salmon are now hybrids between Norwegian and Scottish stock. Chile has also become a major producer of farmed Atlantic salmon, using many of the same brood stocks. The United States is a relatively small producer of farmed Atlantic salmon, although it is a major consumer of these fish, drawing mainly on fish from both Chile and Norway.

How are Atlantic salmon produced in Aquaculture?

There are two major types of aquaculture used for Atlantic salmon. One is referred to as “ranching,” in which Atlantic salmon eggs are fertilized and grown until they are able to live independently, at which time they are released into rivers where they undergo smoltification. They migrate to the ocean to feed, just as non-cultured fish do. When they have completed their sea winters, these fish tend to return to the rivers and estuaries in which they are released, where they are captured and harvested. Ranching of Atlantic salmon has been used extensively in Sweden in the past, and the process also has been used in Alaska and the Pacific Northwest for various species of Pacific salmon. A variant of ranching is called “ocean ranching” in which the fish are released in the ocean, away from rivers and streams with the intent that the fish will return to their release site as opposed to a particular river.
A more common form of current aquaculture for Atlantic salmon occurs in what are referred to as “sea cages” or “ocean net pens.” Briefly, the entire life cycle of the Atlantic salmon is kept under close control. Brood stock (breeding animals selected for a number of traits, including rapid growth under contained conditions, hardiness under contained conditions, good edible yield) are selected when they are almost sexually mature. When they do mature, both females and males are “stripped” of their roe and milt, respectively, and eggs are fertilized under controlled conditions. Fertilized eggs are disinfected and transferred to “hatching trays.” Once eggs are hatched, and alevins emerge, they are moved to tanks and kept under conditions that mimic those in nature (temperatures below 10oC (< 50oF) and relatively dark). Once the alevins have used up their yolk sacs and are ready to feed, they are transferred to tanks and provided with a food supply. At this point the salmon are referred to as “fry” and are grown in tanks with various types of water circulation systems, (or in some cases in natural bodies of water) until they are ready to smolt. At this stage, the fish are about 12 cm long and weigh about 100 grams. Once they have smoltified (adapted to salt water growth), the fish can be transferred to their cages or pens in the ocean.
Salmon aquaculture facility

Image 10: Salmon aquaculture facility

Courtesy: www.salmonfarmers.org

A fish farm can consist of a series of either rectangular or round “pens” which are large nets that are suspended from a series of floating docks, walkways, or cage structures, anchored to the sea bed. Several nets or suspended systems can be linked together to form a “sea site.” Sea sites or individual net pens (or sea cages) are selected carefully—the temperature and salinity of the location are important. Being located in a relatively sheltered spot is also important so that storms do not rip the moorings from the sea beds. Finally, it’s important to be located where there is good water flow to ensure that wastes are carried away and that the oxygen concentration remains at relatively high levels (at least 8 ppm). Fish are generally grown in these systems for about two years or until they reach what the producers deem an appropriate market size (about 2-8 kg (about 4-17 lbs)). In the Bay of Fundy, a typical salmon farm has about 20 net cages in a sea site—each cage is about 8-10 meters deep (24-30 feet). Large sea sites can range from 2-24 acres in total size and contain several hundred thousand fish (www.nwfsc.noaa.gov/publications/ techmemomos/tm49/tm49.htm).
Atlantic salmon require a diet high in protein and lipids. They obtain those nutrients by eating other fish, crustaceans, and zooplankton. Fish farmers must therefore supply a diet that contains fish meal and fish oils. It has been estimated that up to one third of all wild-caught fish are fed to fish in fish farms, usually after being processed into fish meal. Although much of the wastage from fish processing can be used in the production of components of fish meal, it cannot be used directly in fish feeds because of diseases that may be transferred to the farmed fish. Much research is currently ongoing to attempt to supplement fish feed for pisciverous fish with plant- or microbe-based products, but to date, there are no plant-only sources of fish feed for fish that consume meat as part of their diets.
A relatively new method of aquaculture involves growing fish in tanks in inland locations away from the native habitat of the fish. This method of aquaculture is similar to the others described, except that fish spend their entire lives in these fully contained tanks. The tanks may hold either fresh or salt water (Atlantic salmon are able to spend their lives in fresh water, as many live in land-locked fresh water lakes). Temperature, oxygen levels, food delivery, and waste removal are monitored carefully. As the fish increase in size from the 100 gram smolt-size to more market sized animals, they are graded and moved into additional and/or larger tanks to ensure that the density of the animals is kept at appropriate levels (generally less than 50 kg/m3. Fish are harvested directly from the tanks, slaughtered, and sent to market.
Atlantic salmon fillets

Image 11: Photograph depicting Atlantic salmon fillets. Consumer demand for high-quality farmed Atlantic salmon has continued to rise steadily.

Courtesy: www.flickr.com

Especially for fish species whose wild populations are in decline or are endangered, and for which there is a strong market demand, aquaculture may be a solution that allows for providing enough fish to meet consumers’ desires for the kind of fish they like to eat. Many expert bodies, the U.N.’s Food and Agriculture Organization, for one, believe that aquaculture is the only way to meet a growing world population's demand for fish protein in the face of limited wild populations of fish. Some also point out that aquaculture allows for some control over the genetics of the animals being produced, by allowing for selection of breeding animals that will produce relatively disease-resistant, high yielding fish with high quality edible products. It also allows for control over what the fish are fed, and some control over the health of the fish. For producers, in particular, aquaculture allows for better overall control of the product from hatching to slaughter and initial processing, which decreases overall costs, and provides a more consistent, high quality product at the retail end of the market.
As with all agricultural practices, aquaculture involves environmental consequences. These include discharges from site pens of wastes and unconsumed feed that may accumulate on the ocean floor and surrounding environments. Some solutions to this problem involve siting net pen facilities in areas with strong ocean currents that serve to flush the area, as well as letting sea sites sit fallow (empty) for some period of time (often six months) to let the sea floor recover. Many aquaculture facilities also employ video monitoring systems and automated remote feeding equipment to reduce the amount of unconsumed feed. Other concerns include the potential spread of infections in enclosed spaces.

Section 4: Genetic Engineering


Figure 3: Overview of Genetic Engineering

PDF Cover image - Genetically Engineered Animals - Content Update. Click on the image to view the PDF


What are Genetically Engineered Animals?

Genetically engineered animals are produced when genes are introduced into the animals by the processes of modern biotechnology—sometimes these animals are referred to “bioengineered,” or “genetically modified.”  In the U.S. regulatory system, they are referred to as “genetically engineered” or “GE” (See Figure 3).

Genetic engineering has been widely used widely to alter the characteristics (traits) of organisms so that they produce various products. Bacteria and other microorganisms have been produced that make enzymes used in food processing. They have also been engineered to produce pharmaceuticals for human use. For example, most of the insulin sold in the United States is produced in a genetically engineered strain of Escherichia coli that contains a gene for the human form of insulin (Humulin). Many of our staple crops such as corn and soy have been genetically engineered to be resistant to certain herbicides or to contain a protein that is toxic to the caterpillar phase of common pests such as the corn borer. Genetically engineered papaya is resistant to ring-spot virus, which nearly wiped out papaya crops.

FDA has approved one application related to a genetically engineered animal. This is for a goat engineered to produce a human pharmaceutical in its milk. That pharmaceutical has also been approved by the European Medicines Agency (EMEA). In the United States, FDA’s Center for Veterinary Medicine approved the recombinant DNA construct in the goat, and the Center for Biologics Evaluation and Research approved the pharmaceutical (recombinant human antithrombin III) for use in individuals with clotting disorders.

Genetic engineering to introduce new traits (characteristics) is generally accomplished by selecting a gene of interest (a gene is a stretch of DNA that contains the information to code for a protein). In general, scientists join that piece of DNA to what are referred to as “regulatory signals” in a process sometimes referred to as “gene splicing” or “producing recombinant DNA.”
The DNA in almost any cell in an organism contains all of the information required to direct the function of that organism—that is kidney cells from a cow contain all the information to allow a cow to be a cow, as do cells from the ear, or liver, or udder. 
If we think of DNA as a roadmap of information that has instructions for producing substances necessary for life, then it’s easy to see that without additional bits of information that serve as “traffic signals,” cells wouldn’t “differentiate” or take on specific functions. Those “traffic signals” generally tell the cell’s machinery what genes to express and what genes to leave silent. Some of these traffic signals are referred to as “promoters.” These sequences of DNA are usually found in front of genes and tell the cell’s machinery when and where to start processing the information in the gene of interest. 
“Expressing” a gene means that the DNA is “transcribed” into a chemical form (RNA) that can then be “translated” into a protein that actually does something. There are different kinds of promoters. Some are tissue-specific; that is, they only turn on those genes that are supposed to be expressed in a particular cell or organ. Mammary specific promoters, for example, tell the cells of mammary glands to make those proteins and other substances that make milk. Some promoters tell the cell to make some substances all the time—for example, those proteins that are responsible for the day-to-day functioning of the cell. Some promoters tell the cell to make certain substances at specific times during the organism’s life, such as those responsible for sexual maturation. Scientists have attempted to isolate and use the promoters that are best suited for expressing the genes of interest that are being introduced to alter the characteristics of the organism that is being engineered.
In Figure 3, scientists spliced a mammary-specific promoter to the gene of interest—one that contains instructions to make a human protein called antithrombin III, and introduced it into goat early embryos. They then check the resulting goats to see which ones express that protein in their milk, and breed a line of goats that can pass that gene on to their offspring. The females of that herd are used to produce the human pharmaceutical in their milk. http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm143980.htm.

Section 5: FDA’s Regulation of Genetically Engineered Animals


Why does FDA regulate GE animals?

FDA regulates the safety and effectiveness of the rDNA construct which is the piece of DNA added to an animal to change its characteristics or traits, for example to make fish grow faster.) FDA has this responsibility because that rDNA construct meets the definition of a “drug” under the Federal Food, Drug, and Cosmetic Act (FFDCA); the rDNA construct (the piece of DNA added to the animal to alter its traits) is “an article intended to alter the structure or function of the body of man or animal.” As shorthand in this document, we sometimes refer to regulation or approval of the rDNA construct as regulation or approval of genetically engineered (GE) animals. The agency clarified its legal authority to regulate GE animals in Guidance for Industry 187 (GFI 187), which is available at http://www.fda.gov/downloads/AnimalVeterinary/ GuidanceComplianceEnforcement/GuidanceforIndustry/UCM113903.pdf.[1]  
GFI 187 describes, at a fairly general level, the kinds of information FDA needs to evaluate in order to reach decisions regarding safety and effectiveness. We don’t provide specific recommendations in that document because each GE animal and its product pose their own set of risk issues, and so the agency considers them on a case-by-case basis. The Guidance does strongly encourage producers of GE animals to come see the agency early in the process so that they can work with our regulators to prepare the most appropriate data submissions for review.
We intend to release non-confidential materials that we reviewed to assess safety and that the producer submitted to validate the claim that these fish grow more quickly than their non-GE counterparts (effectiveness) prior to the Veterinary Medicine Advisory Committee (VMAC) meeting (see accompanying http://www.fda.gov/AdvisoryCommittees/ CommitteesMeetingMaterials/VeterinaryMedicineAdvisoryCommittee/ucm201810.htm). When you look at these materials, you will see that the agency has received detailed information for the careful evaluation of how the recombinant construct was made, how it was introduced into fish cells, and how the line of fish that have become AquAdvantage salmon were bred. In this document, we will describe the process the agency uses to evaluate any GE animal.

How does FDA evaluate GE animals?

In the overall process described in GFI 187, FDA examines (1) safety of the rDNA construct to the animal; (2) safety of the food from the animal; (3) environmental impact; and (4) the extent to which the producers of GE animals (referred to as "sponsors") have met the claims made for those GE animals (effectiveness). All of these are based on a thorough analysis of the rDNA construct, its integration into the animal’s DNA, and its stability in the animal over multiple generations. GFI 187 describes this in seven steps that we summarize in the following discussion. Each step is dependent on the results of the analysis performed in the preceding steps, so that the review in effect “rolls up” conclusions as it progresses through the entire process.
First, we review data and information on how the construct is made, and whether it contains any pieces of DNA from viruses or other organisms that could pose adverse health risks to the fish or people or other animals eating the fish. We evaluate the rDNA construct to determine whether pieces of DNA came from viruses that could intermix with similar viruses (in that species or other species with which it has close contact) and perhaps create a new virus that could pose health risks, similar to the way that avian flu arose. We also look to see if any pieces of the construct will make new proteins (except for the intended ones) that could possibly cause health concerns. GFI 187 refers to this analysis as the “Molecular Characterization of the Construct.”  
Second, FDA evaluates studies submitted by the producer to determine what happens when the rDNA construct is incorporated into the animal, and how it behaves over multiple generations in what GFI 187 refers to as the “Molecular Characterization of the GE Animal Lineage.” This includes analyzing whether the construct remains in the same place over time, and whether animals continue to express the trait (characteristic) that the construct is supposed to introduce.
Third, FDA determines whether the rDNA construct is safe for the resulting line of GE animals by performing what GFI 187 refers to as the Phenotypic[2] Characterization. We do so by reviewing studies that characterize the actual GE animals over several generations. Questions that the agency asks include whether the resulting GE animals look like their "regular” counterparts by comparing them to both closely related animals and to animals of the species in general. The agency asks whether the GE animals are healthy, including disease resistance, and whether they reach the same developmental milestones that comparison animals do. Another safety question that is evaluated is whether there are any abnormalities that would not be found in other relatives of the Ge animal which might express similar traits, but via conventional breeding. For example, if an rDNA construct were introduced to make the animal grow faster, would close relatives that had been selected to grow faster via other assisted reproductive technologies or natural breeding show any effects that could be due to fast growth? In addition, we are evaluating the results of necropsies (examinations of the bodies and tissues of animals that have been sacrificed for that purpose) to make sure that cells, tissues, and organs look normal. We also assess the results of the kinds of tests that doctors might perform on people when they get a physical, such as blood cells, blood chemistries, etc., to determine whether the animals not only look healthy, but also that their bodies are functioning appropriately. We evaluate the actual chemical composition of edible fish tissues to make sure that there are no substances in the tissues that could harm the GE animal or people who eat it, if it is intended for food use.
Fourth, we perform what GFI 187 calls a Durability Assessment. This reviews the plan that the sponsor will agree to in order to ensure that the GE animals produced in the future will be equivalent to the GE animals that we evaluate as part of the pre-approval review. This involves returning to some of the data presented in the characterization of the lineage of GE animals described in the second step, to ensure that the rDNA construct remains stable in multiple generations of the GE animal, and reviewing the plan that the sponsor is proposing in order to monitor subsequent generations of the GE animals.
Fifth, if the GE animal is intended to be used as a source of food, FDA assesses whether it is safe to eat the GE animal. This evaluation relies on information gathered in the parts of the application that look at the rDNA construct and the health of the animal. FDA experts in food safety look carefully at the composition of the edible tissues of the GE animal to determine whether its meat or milk or eggs differ in any way that affects safety or nutrition from the non-GE counterparts that we eat today. These experts evaluate whether the levels of key substances such as proteins, fats, minerals, and vitamins are in the same range as they are in the food we eat from conventional animals. If there are any differences, FDA must determine that there is a reasonable certainty of no harm from any of those differences.
In addition, FDA’s food safety experts evaluate data to determine whether the GE animal poses any more allergenicity risks than its non-GE counterparts currently on the market. There are eight food groups that cause about 90% of all of the food allergies that people have. These include peanuts, tree nuts (such as almonds, filberts, and Brazil nuts), milk, eggs, wheat (not to be confused with gluten intolerance), soy, finfish, and shellfish. If the GE animal is one to which people already tend to be allergic, it is likely that they would avoid that species in order to avoid an allergic reaction. For example, if people are allergic to shrimp, they would not likely eat GE shrimp.  Regardless, in this part of our evaluation, we will look to see whether the GE animals are more allergenic –that is, pose more of an allergic risk, than their non-GE counterparts.


Sixth, the agency evaluates the environmental assessment associated with the conditions proposed to raise the GE animal. As part of the approval process, the agency must meet the requirements of the National Environmental Policy Act (NEPA). NEPA requires that all federal agencies evaluate whether certain actions (in this case, the approval of a GE animal) will have an impact on the environment. Except in those circumstances where an environmental assessment (EA) is not required because the type of action does not have a significant impact on the environment, we do this by evaluating the results of an environmental assessment (EA) for the specific conditions of use of a particular application. If we find, based on a review of the EA, that there is no significant impact on the environment under those conditions, we publish a Finding of No Significant Impact (FONSI). The EA is a public document. If we do find that there is an impact, a considerably more extensive assessment is required—the Environmental Impact Statement, in which the nature of the anticipated impact(s) are reviewed in detail.
There have been some concerns about the effects that intentionally released or escaped fast-growing fish would have on wild stocks of Atlantic salmon. When FDA approves a new animal drug application for a GE animal, it will generally be for a specific set of conditions of use. For GE animals, this includes the location and containment conditions. Containment is a term that encompasses any technique that keep animals from leaving a physical space, or that keeps them from interbreeding with other populations.
There have been some concerns about the effects that intentionally released or escaped fast-growing fish would have on wild stocks of Atlantic salmon. When FDA approves a new animal drug application for a GE animal, it will generally be for a specific set of conditions of use. For GE animals, this includes the location and containment conditions. Containment refers to keeping animals from leaving a physical space, or from establishing a population in an undesirable location.
There are a number of containment strategies. Containment systems that have multiple overlapping controls are more secure than those that have single controls. Three different types of containment strategies that are used in overlapping form for growing fish (including those that have not been genetically engineered) are:
  1. Physical containment.  Fish are kept in a different physical environment either in a different location or by using physical barriers. For example,
    1. Sea-dwelling fish raised in inland tanks far from the ocean
    2. Physical barriers  (e.g. screening) placed at possible points of escape for small fish, such as water and waste pipes
    3. Netting placed over tanks to keep fish from jumping out or, if outdoors, to keep fish-eating birds from preying on them.
  2. Geographic/Geophysical containment. Taking advantage of climate and other conditions, e.g., by siting an aquaculture facility in conditions unfavorable for fish to survive if they were to escape, such as still, silty, and warm water for a fish that needs high dissolved oxygen content and low temperatures.
  3. Biological containment, which is generally thought of as a way to limit the spread of a population, and includes
    1. Inducing sterility. Pet owners exercise biological containment by neutering their cats and dogs. Many fin- and shell-fish are made sterile by inducing “triploidy” so that the cells that make eggs fail to develop properly (see Figure 4).
    2. Using only a single-sex population of the animal as the production animal.


Figure 4: What is Triploidy?

Triploidy is a form of “biological” containment. It is a way to make the population largely sterile. Most of the cells in the bodies of animals are diploid—they have two sets of chromosomes, one from their female parent and one from their male parent. Gametes, the male and female sex cells (eggs and sperm) are haploid—they have only one set of chromosomes. Triploid cells or organisms have three sets of chromosomes.

Triploid organisms can occur naturally, often in plants: bananas, apples, seedless watermelons, ginger, and some citrus are triploid, for example. Triploidy can occur naturally in some fish. Although it has not been successfully induced in birds or mammals, it can be induced in fish by treating fertilized eggs for a brief time with extreme physical means (higher than normal pressure or different temperatures, either warmer or colder than usual). Examples of fin- and shell-fish in which triploidy has been induced include oysters (food and pearl), mussels, scallops, clams, shrimp, trout, salmon, sea bream, tilapia, and catfish.

Triploidy is often employed in animals that are used for food for several reasons including wanting to have a sterile population. Most triploid animals are sterile because they don’t reach sexual maturity and cannot produce sperm or eggs. Sexual maturation requires a great deal of energy, energy that can otherwise be used for growth. Finally, sterility is a way of keeping organisms from reproducing, thereby avoiding the possibility of their establishing a population in an ecosystem in the event of an unanticipated escape, or preserving intellectual property.

Fish scientists have looked carefully at the difference in texture, color, and composition in both diploid and triploid Atlantic salmon and have found that any difference that may be detected is due to variability between individual fish, and not because some fish are triploid and some are diploid (Bjornevik et al. 2004).



In the seventh and final step, that sponsors submit in support of their claims for the GE animal. (For conventional article regulated as drugs, this is referred to as “effectiveness.”) For example, for the GTC goat, FDA determined that the goat did indeed produce human antithrombin in its milk. For an animal that is intended to grow faster, the agency will need to evaluate data that shows that the GE animals do indeed reach some size or weight more rapidly than their conventional counterparts.

What information about this evaluation will be released to the public?

FDA will present the key information that the agency has evaluated, with any confidential information redacted, to the Veterinary Medicine Advisory Committee at a public meeting to be held on September 20, 2010.  FDA anticipates making the meeting materials available approximately two weeks before this meeting, but in any event no later than 2 business days before the meeting.


How will FDA decide on labeling for GE animals?


Labeling must accompany any GE animal, including any life stage. For large terrestrial animals, identification is relatively straightforward (see the description in the Freedom of Information Summary for the GTC Goat Approval) http://www.fda.gov/downloads/AnimalVeterinary/ DevelopmentApprovalProcess/GeneticEngineering/GeneticallyEngineeredAnimals/UCM163814.pdf
In the case of fish, individual identification and labeling is more difficult, It is likely that the agency would require that containers in which live fish, eggs, or milt are transported or reared will be required to have a label that clearly identifies them as GE fish, and that includes any special instructions that may be necessary for growing the fish.


With respect to labeling food from AquAdvantage fish, the agency is in the process of determining whether any special labeling would be required. Because this is the first time the Agency is considering an application for a genetically engineered animal intended for use as food, FDA will hold a hearing at which it will explain the relevant labeling principles, and the public will be invited to share its views on the application of the relevant legal principles of food labeling to food from the AquAdvantage Salmon.  See http://www.fda.gov/AdvisoryCommittees/ CommitteesMeetingMaterials/VeterinaryMedicineAdvisoryCommittee/ucm201810.htm for a discussion of the issues associated with labeling of food from the AquAdvantage salmon if it were to be approved.

How does the agency announce decisions on GE animal approvals?

FDA publishes all of its approvals for new animal drugs, including the rDNA construct in GE animals in the Federal Register, in a publication called the “Green Book,” and on Animal Drugs @ FDA.
When the agency issued GFI 187, we said that we were interested in enhancing the transparency of our decision-making processes, and at present we intend to hold a public VMAC meeting before we approve a GE animal application. We will be holding such an advisory committee meeting on Sept 19, 2010 for the AquAdvantage Salmon (as announced in the accompanying Federal Register notice). 
We are also aware that the public has an interest in labeling of food from the AquAdvantage salmon. We will also be holding a meeting to accept public comment on food labeling after the VMAC meeting (see http://www.fda.gov/AdvisoryCommittees/CommitteesMeetingMaterials/ VeterinaryMedicineAdvisoryCommittee/ucm201810.htm).

Where can I get more information on salmon, aquaculture, or AquAdvantage Salmon?

We have provided a bibliography that lists several sources of information on these topics. We also encourage you to visit websites for other government agencies that have considerable expertise in fish, fisheries, and the environment. We have provided some links in the bibliography. We remind you that the veterinary medicine advisory committee meeting to discuss FDA’s review of Aqua Bounty Technology’s application is open to the public, and FDA anticipates making the meeting materials available approximately 16 days before this meeting, but in any event no later than 2 business days before the meeting.



Benfey, T. “Use of Sterile Triploid Atlantic Salmon (Salmo salar L.) for Aquaculture in New Brunswick, Canada.” ICES Journal of Marine Science. 58 (2001): 525-529.
Bjornevik, M. “Temporal Variation in Muscle Fibre Area, Gaping, Texture, Colour, and Collagen in Triploid and Diploid Atlantic Salmon (Salmon salar L).” Journal of the Science of Food and Agriculture. 84.6 (2004): 530-540.
Fay, C., et al. Atlantic Salmon Biological Review Team. “Status Review for Anadromous Atlantic Salmon (Salmo salar) in the United States.” National Marine Fisheries Service and U.S. Fish and Wildlife Service, 2006.
Hallerman, E.M., et al. “Effects of Growth Hormone Transgenes on the Behavior and Welfare of Aquacultured Fishes: A Review Identifying Research Needs.” Applied Animal Behaviour Science. 104 (2007): 265-294.
Hindar, K., et al. “Genetic and Ecological Effects of Salmon Aquaculture on Wild Salmon: Review and Perspective.” ICES Journal of Marine Science. 63(2006): 1234-1247.
Knapp, G., et al. “The World Salmon Farming Industry.” The Great Salmon Run: Competition Between Wild and Farmed Salmon. TRAFFIC North America, Washington D.C.: World Wildlife Fund, 2007.
National Research Council of the National Academies. Atlantic Salmon in Maine. Washington D.C.: The National Academies Press, 2004.


Naylor, R., et al. "Feeding Aquaculture in an Era of Finite Resources." Proceedings of the National Academy of Sciences of the United States of America. 106:36. (2009): 15103-15110.


Willoughby, S. Manual of Salmonid Farming. Malden, Massachusetts: Blackwell Science, 1999.
Verspoor, E., et al., ed. The Atlantic Salmon: Genetics, Conservation, and Management. Oxford: Blackwell, 2007.



Selected Salmon Web Resources

National Marine Fisheries Service
U.S. Fish and Wildlife Service
U.S. Department of Agriculture
U.S. Food and Drug Administration
Aqua Bounty Technologies
Aquaculture Network Information Center

[1] See this guidance document for further explanation of FDA’s legal authority with respect to GE animals and citations to sources of authority.


[2] Phenotype refers to the physical characteristics of an organism (its expressed traits).