Aquaculture - A Study in Marine Science by Donald E. Chase

Aquaculture is considered a form of agriculture. Unlike commercial fishing, which is concerned mainly with the harvesting of marine plants and animals, aquaculture involves the propagation, cultivation, and marketing of aquatic animals and plants in a controlled environment. A wide array of marine organisms are produced through aquaculture, including fin fish, crustaceans, mollusks, eels, seaweed, and algae. Aquaculture in the United States represents a small segment of agricultural production, but it is relatively young and growing industry. According to the National Marine Fisheries Service, aquaculture production in the United States has grown from 170,451 metric tons in 1985 to 314,657 metric tons in 1996, a growth of 85% in just 11 years. Presently, according to the U.S. Department of Agriculture, 175,220 active acres of ponds are to be in use during 1999.

Fish farming has been practiced throughout the world for thousands of years. As early as 4,000 years ago, the ancient Chinese were raising common carp. Hieroglyphics in the tombs of Pharaohs depict farming of tilapia in ancient Egypt. The Romans built small ponds for raising fish. A few centuries later, the culturing of mollusks and oysters was introduced by the French and Japanese respectively when they discovered that mollusk and oyster spat (newly settled juveniles) would settle on upright posts in the ocean. Pond fertilization was introduced in Europe in the sixteenth century when it was discovered that manure added to water encouraged the growth the plankton, organisms at the bottom of the marine food chain.

In the United States, aquaculture can be traced back to the middle to late 19^th century. Commercial fish farming began in the United States in the middle 1850s with the production of rainbow trout. The bait fish industry began in the early 1900s to satisfy the demand by sport fishermen. Until the 1950s, U.S. aquaculture was comprised mainly of rainbow trout, baitfish, and a few warm water species. Channel catfish farming began in the United States around 1955. For the first 15 years or so, the catfish industry was limited to a few states in the southeast, but now catfish are produced in numerous states, including Idaho, California, Kansas, Missouri, and most Southern States. In the early 1990s, Mississippi was dominant in the industry with 59 percent of the acreage and 75 percent of the production. Catfish is now the number one aquaculture species both in terms of dollars produced (estimated in 1996 at $364,951,000 - 41% of total production) and metric tons produced (estimated at 214,154 metric tons in 1996 - 68%). Other important species include trout, crawfish, salmon, bait fish, oysters, tilapia, striped bass, clams, shrimp, and mussels.

Species	Metric Tons	Thousand Dollars
Catfish	214,154	364,951
Trout	24,322	56,958
Crawfish	21,130	34,820
Salmon	13,906	60,995
Bait fish	9,457	70,254
Oysters	8,412	64,368
Tilapia	7,242	23,948
Striped Bass	3,561	20,308
Clams	1,739	20,315
Shrimp (saltwater)	1,300	11,464
Mussels	447	5,085
Other	8,987	152,169
Totals	314,657	885,635

There have been significant increases in demand for fish and seafood in the United States and throughout the world. In the United States, per capita consumption rose from 12.5 pounds in 1980 to 15.5 pounds in 1990 (as compared to a global average of 41.8 pounds). This is expected to continue to increase as consumers become more health-conscious and demand the nutritional benefits fish products provide, and as the general market for fish products continues to expand, making fish products a well-priced alternative to meat products. Additionally, the current strong economy in the United States exerts an influences on aquaculture, leaving U.S. consumers with more disposable income for away-from-home eating, and leaving feed costs low for the aquaculturists, decreasing overall seafood prices and making it an attractive alternative to other food sources.

Methods used to cultivate marine life are as varied as the organisms themselves. Many factors determine the specific production method used, including location, water supply, type of organism to be raised, etc. Although there are many different methods that can be used, for the production of aquaculture, the most common are ponds, cages, raceways, and tanks. Many different production methods also exist for shellfish cultures.

Earthen ponds are the most common production system used. These ponds may be anything from a small farm pond to a commercially-created pond, specifically designed and built for aquaculture. Pond systems which can be drained are preferred over closed ponds since the ability to change and treat the water can prove important in cases of bad water quality or disease. Ponds that are constructed for fish culture are called dike or levee ponds. The types of levee ponds are holding ponds, spawning ponds, rearing ponds, and grow-out ponds. Production level for ponds can range from 2,000 to 10,000 pounds per acre per year.

Cage culture can be applied in existing bodies of water that cannot be drained or seined, and large bodies of water that would otherwise not be suitable for aquaculture. Using cages to culture fish utilizes existing water resources (i.e. lakes, reservoirs, ponds, or the sea), but encloses the fish in a cage or basket, which allows water to pass freely between the fish and the water source, but keeps the fish contained and ready to harvest. Cages can either be floating (with the floatation provided by metal or plastic drums or PVC pipe, or styrofoam) or can be standing (secured by stakes driven into the bottom of the body of water). Cages vary in size shape, and material used in its construction. One of the key points to be taken when considering cage culture is that total production is not greater in cages than if the fish were released into the water itself. In fact, good water circulation is more important to assure that eutrophication does not occur in the area surrounding the cage. Production rates of cages can be similar to ponds.

Rectangular raceways are used almost exclusively for trout production. Raceway facilities require large quantities of inexpensive high-quality water. Water is normally obtained from a spring or stream and is passed through the raceways using gravity. This type of system is normally called a "once-through" or "open" system. Raceways can be earthen, or can be built out of concrete, wood, block, tile, or another durable material. Sometimes, the culture water is pumped back through a processing reservoir where wastes are removed, although this type of system is much more labor and cost restrictive. Production in raceways is normally higher than in ponds or cages because of the continual exchange of fresh water, which removes wastes and adds fresh oxygen. Production in this type of system is measured in pounds per gallon of water per minute, with yields obtained exceeding 20 lb./gal/minute.

The use of tank cultures is a good alternative to pond, raceway, or cage culture if sufficient water or land is not available, or if an aquaculture establishment is desired in a location that would otherwise be unavailable, such as a warehouse within a city. The main advantage to a tank culture is that it is extremely easy to control all the environmental conditions such as water temperature, water quality, waste disposal, dissolved oxygen levels, etc. Since the water is recirculated, rarely does the system require new water to be added. Another advantage is that with correct conditions, high fish densities are attainable and the stock is easier to manage. It is easier to localize disease control compared to ponds and raceways. However the higher density does lead to higher stress levels, a major factor in the outbreak of disease, and since there is limited access to natural foods, they must be fed a complete diet – increasing total production costs. Also, the mechanical costs are much higher for filtration, aeration, and pumping systems. Overall, production levels are much higher, with monthly yields ranging from 0.4 to .06 lbs/ft³ of water.

The methods used to culture shellfish are just as varied as those for fin fish. These systems include: planting beds in or on the ocean bottom; near bottom cultures using cages and boxes of plastic to culture clams or oysters just off the bottom; water column cultures suspending clams, oysters, mussels, or scallops using floatation devices; surface floatation systems using mesh containers to float shellfish near the warmer surface waters; and land-based systems, which normally are used only during the early stages of shellfish development before planting. Some shellfish culture systems require more maintenance than others do, most importantly, many require defensive measures be taken against predators, and shellfish culture systems in the North require attention be paid to potential ice damage.

Naturally, considering the nature of aquaculture, water is the most important factor in selecting the proper location for an aquaculture facility. Aquatic organisms require water to breathe, eat, grow, and reproduce. Sources of water include the ocean, wells, springs, streams, rivers, lake, and municipal water. When looking at the quality of the water, many factors must be considered, but most importantly are temperature, dissolved oxygen, salinity, pH levels, and ammonia levels.

Fish are cold-blooded organisms that assume the same temperature as their surroundings. Many biological functions are tied to temperature, including metabolism and mating habits. When choosing an aquaculture site and fish to be produced, selection should be based on the temperature of the water supply.

Fish require oxygen for respiration. Dissolved oxygen levels should be greater than 4 to 5 ppm (parts per million) for optimal growth. In addition to needing dissolved oxygen in the water for fish to breath, it is also required since oxygen is consumed by the breakdown of fish wastes and (on aquaculture ponds) uneaten feed.

Fish excrete ammonia into the water as part of their waste. Two forms of ammonia occur in aquaculture: ionized (NH₄⁺) and un-ionized (NH₃). The un-ionized form of ammonia is toxic to fish, ionized ammonia is not. Normally, toxic ammonia is degraded to harmless nitrates through biological processes. In nature, this natural process is adequate enough to remove the toxic ammonia from the water. However, in an aquaculture setting, with a much higher density of fish, the potential for toxic ammonia build-up is much higher, so aquaculturists must always be monitoring ammonia levels in order to assure that the build-up does not become harmful to the fish being cultured. Additionally, mechanical filtration is used in some ponds to remove the ammonia (as well as aerate the water). The pH level of the water influences the toxicity as well. For example, in areas where water pH is low (6.5 to 7.0), it is possible to reuse water six or more times before un-ionized ammonia reaches toxic levels. However, in alkaline water where pH values are 8.0 or above, only limited water reuse is possible.

There are a great number of aquatic species that have commercial production potential. However not all aquatic species with economic value are candidates for commercial culture. Many aquatic species have specific environmental requirements for life and optimal growth. For example, rainbow trout die at water temperatures above 70° F, and flourish at a temperature of 55° F, while catfish die at temperatures above 95° F, and grow at an optimal rate at 83° F. In addition, there are regional advantages to some production locations over others. Southern states are better suited for the catfish industry than the northern states, since catfish will take twice as long to grow in the northern states and rainbow trout are better suited for colder climates.

This is the most common form of aquaculture practiced throughout the world. The most common finfish and shellfish grown in the United States are catfish, trout, salmon, carp, crayfish, freshwater shrimp, striped bass, and tilapia.

The exact size of this segment of the industry is not well known. However, nearly all states east of the Rocky Mountains have some form of bait farming. The most common species produced include golden shiners, fathead minnows, goldfish, carpsuckers, bluntnose minnows, tilapia, suckers, and crayfish.

The ornamental fish, plant, and snail industry can be divided into two groups. The first group is the tropical fish and plan industry, which is originated in the state of Florida. The second group includes fish that would be grown for use as ‘feeders’. Most tropical fishes and plants do not tolerate lower temperatures, and would not thrive in other parts of the country, however potential does exist for the indoor cultivation of these animals in a controlled environment.

Fee fishing ponds are usually small, heavily stocked bodies of water containing one or more kinds of fish that are of legally catchable size. Generally, the operator of the pond charges a fee (normally per pound of weight or inch of length) for each fish caught. The types of fish stocked normally depends on the condition of the pond – cold water ponds are normally stocked with trout, while warm water ponds are normally stalked with channel catfish, bullheads, and hybrid sunfish.

With the large number of farm ponds throughout the country, the production of sport fish to stock them can be a very profitable business. Additionally, fish are sometimes supplied to stock city or county lakes. Normally, fish are stocked at below catchable size and then grow more in the ponds.

Aquaculture products are often raised by biological supply houses for use by educational and research institutions. This type of aquaculture is more rare, and care must be taken in choosing the exact species to be raised and marketed.

One of the most important issues in aquaculture is disease control. Without proper controls, entire species of aquatic organisms can be threatened. Factors that lead to a culture having a susceptibility to a disease introduction include improper storage of feed, chronic exposure to ammonia, introduction of foreign parasites into local waters, and stress. Stress is an important factor because a healthy, stress-free fish are able to fight off disease, but once a fish becomes stressed, the effectiveness of the immune response is diminished. Sources of stress include handling, sudden changes to water temperature, low dissolved oxygen rates, and poor nutrition. Overcrowding is also another concern. It is not uncommon for tens of thousands of salmon to be raised at one time in a medium-sized fish farm. This overcrowding leads to stress, which leaves the salmon susceptible to disease breakouts. Since the fish are raised in such a confined area, the disease spreads quickly, wiping out the entire culture at once. An ocean environment exposes the entire surrounding ecosystem to possible disease contamination, so extra care must be taken in the monitoring of fish stock.

Another high-risk disease concern in aquaculture is the importation of species. Many times, organisms from one area are transplanted to another, carrying with them a disease strain that native organisms are resilient to, but can wipe out the local species. The Spring 1999 issue of Ocean Realm details a pair of incidents involving imported Scottish salmon in both Ireland and Norway. Ireland’s sea trout population suffered catastrophic losses when local salmon farm stocked with the Scottish salmon served as an incubator for sea lice, which infected the local sea trout population. A similar tragedy occurred in Norway, when a parasite called Gyrodactylus salaris, which was harmless to the Baltic salmon population, was exported to Norway with the Baltic Salmon. The parasite began killing 500,000 to 1,000,000 pounds of Norwegian salmon annually. Finally, in an attempt to eradicate the G. Salaris parasite, entire river systems were poisoned with a substance called rotenone in an effort to call all life and start over. A similar outbreak was caused with the introduction of a foreign strain of furunculosis in 1985, which affected over seventy-four river systems and threatened the entire wild stock of Norwegian salmon.

Techniques used to treat infected cultures include prevention measures, actions to clean and disinfect ponds, and the use of various immunostimulants, vaccines, and antibiotics. When considering the use of vaccines and antibiotics in aquaculture environments, it is important to consider the effects that any changes can have on the total ecosystem. For instance, it is best to use those that break down quickly and do not pass up through the food chain, especially considering that most aquaculture products are intended for human consumption. Also, any efforts taken to effect just the culture raised can have adverse affects on other aspects of the ecosystem – such as the complete loss of life in the Norwegian river systems when rotenone was added to eradicate the G. Salaris parasite.

Aquaculture provides people with a great source of nutritious, high-quality food. However, similar to conventional agriculture, there are many adverse environmental impacts to aquaculture. The most important effects are ecological, and these are normally associated with the conversion of natural ecosystems into complex and intensely managed aquacultural ecosystems. For example, in the March/April 1998 edition of Worldwatch Magazine, it was reported that:

Fishes raised in ocean cages have an impact on the ecosystem as well. Although they may be closed-in, their cages are normally made of mesh or wire that allow for the complete exchange of water into and out of the culture area itself. Waste effluent can effect the outside environment, potentially contaminating it with parasites and disease, and some of the environmental controls exercised on the cultured fish (such as lighting to stimulate growth rates, fertilization of water to encourage phytoplankton growth, etc.), naturally affects the entire ecosystem surrounding the fish farms.

Additionally, predator control methods used by fish farms has an adverse effect on the surrounding environment. In some areas, aquatic noisemakers are used to discourage sea lions and the like from feasting on the caged fish. However, these also have the effect of scaring away other marine life, most notably the whale population. If the predators become too aggressive, aquaculture farmers are allowed to kill the predators to protect their stock – but many times farmers have been too quick to sentence a suspected predator to death, even those who in fact have had no direct contact with the farm.

As is the case throughout the world, Massachusetts is a prime location for aquaculture. Within the state, there are over 3,800 lakes and 4,000 miles of rivers and streams. The state operates at least five fish hatcheries and one lobster hatchery. In addition, many regional research centers exist in this area, including the Northeastern Regional Aquaculture Center at the University of Massachusetts at Dartmouth, the MIT / Massachusetts Maritime Academy Sea Grant Fisheries program, the New England Aquarium in Boston, and the Woods Hole Oceanographic Institution

The major products of Northeastern aquaculture industry are oysters, salmon, hard clams and trout. Other species grown in the region include hybrid striped bass, tilapia and mussels. Total production has grown to an estimated value of $146.4 million in 1992. The lobster hatchery helps support the multi-million dollar lobster market by hatching and stocking lobster larvae. The Bay State hatcheries supply hundreds of thousands of trout, Atlantic salmon, northern pike, and tiger muskies.

In Boston, Mayor Thomas Menino has suggested turning an antiquated former sewage treatment tank system located on Moon Island into an aquaculture fish farm. After six months of study, the project stalled out amid environmental concerns about sediments discovered on the tanks’ floor, and concerns about the ability of fish to grown in the rather cold temperature of the water from Boston Harbor. The estimated cost to clean up, roof (for heating), and prepare the site ranges from $11 - $40 million depending upon the level of fish hatching expected at the site.

Other ventures have been considered in Boston as well. According to The Wall Street Journal, Legal Sea Foods, Inc. is working on plans to lease a 30,000 square-foot site on the waterfront in South Boston to raise red drum, haddock, and summer flounder. Additionally, the Boston Redevelopment Authority and New England Aquarium are planning to build an "urban aquaculture institute" comprising of a training center for fish farmers, a public education facility and a business incubator. Moon Island is one of the sites being considered for the site.

Although aquaculture has been around for thousands of years, it has only been during the few decades that we have seen a true expansion in national and local interest in aquaculture as a viable alternative to traditional fish harvesting. However, the growth of Aquaculture has been astounding. According to The Washington Post in an article on November 30, 1997, "Preliminary industry statistics this year indicate that, for the first time, there will be more farm-produced salmon on world markets than fish caught in the wild." Although that is not the trend for all species, we have seen the overall rate of growth for aquaculture-produced animals greatly exceed the rate of growth for fishes caught in the wild. When you combine this fact with the facts that consumers are becoming more health conscious, that there are health and environmental concerns about the edibility of some of the fish caught in the wild, and that as more aquaculture ventures are started, overall prices of seafood will come down, it may not be long before most of the world’s population are fed seafood which are hatched, raised, and grown-out in an aquaculture environment. Aquaculture is not a cheap venture, as Boston’s Moon Island plan so greatly illustrates, but the possibilities are endless. Unlike traditional farming that relies on finding an adequate piece of land to start, an aquaculture venture can exist almost anywhere. Ventures can be started in a warehouse in the middle of a busy city, or in a man-made fishpond in the middle of nowhere. Naturally an aquaculture venture can also be started anywhere where there’s water- from the shores of different countries, to any lake river, or stream, and naturally, the ocean. The possibilities of what to grow are just as endless.

However, the euphoria that comes with the possibilities that exist about an aquaculture venture must be greatly balanced with concern for the environment around it, especially when aquaculture ventures are based in a pre-existing ecosystem. Care must be taken to ensure that any aquaculture venture is ecologically compatible with it’s environment, or else disaster can strike, not just to the stock being raised, but to the environment around it as well.

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Aquaculture A Global and Local Perspective

Aquaculture
A Global and Local Perspective