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Vegetarian Journal Cover

Vegetarian Journal

Excerpts

May/June 1997
Volume XVI, Number 3





Aquaculture: An Overview

By Jeanne-Marie Bartas



To view the references for this article, click here.

Introduction

At one time or another you may have seen a ten-gallon aquarium containing a multitude of small, tropical fish species. Or, you may have seen the fresh fish display at a large supermarket. Have you ever wondered where those fish came from?

We have. In fact, the motivation for writing this piece stems directly from the scarcity of articles on this topic. When an article related to animal agriculture appears in vegetarian publications, it is most often about cows, chickens, or pigs. It is true that fish raising on a commercial scale is new. This is a large part of the reason why so little has been written about it. And when something about fish does appear, it is typically about seafood safety concerns. While the latter is an important issue of concern to all consumers, we wanted to focus on other aspects of the fish industry.

We were particularly interested in the environmental and ethical ramifications of fish raising. Thus, in Part I of this article, we will examine water usage and genetic engineering in the fish industry. In Part II of this article, we will consider drug regulation in aquaculture. We will also discuss effluent and solid waste control and some of the global environmental impacts of aquaculture. Our objective is to present factual, current information which will help the reader in his environmental and ethical assessments of aquaculture. It is important to note at the start that the fundamental ethical question, i.e., whether the killing of fish and other sea animals for food is morally right, will not be addressed. This question could be the subject of a doctoral dissertation. Our more humble aim in this article is to help the reader assess the current system of raising fish and other sea animals for food from an environmental and ethical point of view.

Background

Up until thirty or forty years ago, most fish intended for human consumption came from the wild.(1) When scientific fish farming_more appropriately called aquaculture_began in the West on a large and profitable scale, several major industries were born. Catfish farming in the southern United States and salmon farming off the Norwegian coast were the largest industries. Now, the farming of all types of aquatic organisms, including plants, animals, and microorganisms, has become popular. The rearing takes place in controlled environments and has the explicit goal of producing profit-yielding items which appeal to the human palate. Today's aquaculture is a multi-million dollar enterprise. Total U.S. production in 1992 (of fish, shellfish, and plants), was over 310,000 metric tons with productional income totaling $724 million.(2) However, only 9% of the seafood eaten in America comes from aquaculture. The world average is 16%.3 The majority is either imported or captured wild stocks. This is expected to change as wild fish stocks remain stable or are in decline and as the per capita consumption of aquatic foods in the U.S. increases.(4)

At the present time, the U.S. imports approximately 60% of its fish and shellfish.(5) Fisheries imports are the second largest contributor to the U.S. trade deficit, second only to petroleum products, among natural resources products.(6) The importation amounts to a $3.3 billion annual trade deficit. Some individuals believe that the expanding aquacultural industry can help alleviate this national burden.

The alleviation of the U.S. trade deficit is no easy matter. This applies to aquaculture's efforts to do so as well. To be lucrative, aquacultural methods must be semi-intensive, intensive, or super-intensive; i.e., raising large numbers of fish in confined and carefully controlled areas. This means that specially formulated foods, electrically-operated aerators, and elaborate water filtration systems must be used in order to yield, for example, 1.5 pounds of fish per gallon of water, or up to 50,000 pounds of fish per acre.(7) These methods are very different from the extensive methods still in use in some developing countries, in which minimal technological intervention occurs.

In this article we will take a close look at modern U.S. aquaculture. We will see that aquaculture's current face resembles little its humble beginnings in ancient China (3500 B.C.) or Japan (2000 B.C.) where carp and oysters, respectively, were raised.8 For the record, aquaculture began in the Western world during the times of the ancient Romans who raised fish in brackish water along Italy's coast.(9)

Aquacultural Management

There are many aspects which an aquaculturist must consider in the day-to-day raising of fish and other sea life. In this discussion, we will focus on fish raising even though much of the discussion is applicable to the raising of other sea animals, such as shrimp, and of sea plants.

To an aquaculturist, the source and quality of the water and feed are vitally important for a good harvest. Furthermore, both the water and feed qualities are necessary factors in determining the health of the fish. Let us now turn to these topics.

Water Source and Quality

There are three main sources of water in aquaculture: ground water (i.e., water beneath the earth's surface which supplies wells and springs), municipal water, and surface water (i.e., ponds, rivers, streams, and oceans). In catfish production, for example, a ground water source for the rearing ponds is preferred because ground water eliminates the worry about unwanted fish mixing with the commercial fish. Ground water also removes concerns about the diseases which surface water may carry, and its seasonality.(10) However, ground water may be expensive because of the necessary well installation and pumping costs. Municipal water is a possibility which has not yet been fully exploited.

Filling and maintaining a pond takes large quantities of water. According to one Southern Regional Aquacul-ture Center publication, "Approximately one million gallons of water per acre are required to fill a pond and an equivalent volume is required to make up for evaporation and seepage during the year. This means that approximately 400 gallons are required per pound of production."(11)

Water is also a serious consideration for trout farmers who depend on a continuous water flow of at least 500 gallons per minute.(12) In fact, a major constraint in the trout industry, which is showing signs of stagnation, may be the availability of sufficient supplies of cool, clean water.(13) Between 5,000-10,000 gallons of flowing water are needed to produce one pound of trout.(14)

In light of growing difficulties in finding an ample supply of clean water, many farmers raise their aquatic species in recirculating tank systems. These systems, through water treatment and reuse, utilize less water than do ponds in order to produce similar yields. However, the technology is costly. To date, there are relatively few reports of profitable commercial aquaculture recirculating production systems in operation.(15)

Despite their costs, recirculating systems are the most common method for raising the Tilapia species, a member of the cichlid family of fish. Tilapia is relatively new to U.S. aquaculture, but it is becoming a very popular species because of its ability to tolerate crowded conditions and poor water quality and still maintain its taste and rapid growth rate from lower-qual ity feeds. In fact, Tilapia is such a prolific breeder that there is a concern that if the species got into the wild, it would become uncontrollable.(16) As a result, Tilapia is almost always raised indoors.

Water quality is also important to the aquaculturist. There is no question that without a suitable living environment, aquatic species will either give poor yields, or no yield at all. It is imperative that adequate levels of dissolved oxygen and minimal levels of carbon dioxide be maintained at all times.(17) For intensive systems, there are several ways in which to accomplish this goal. These include the use of air diffusers and surface agitators.(18)

Another critical parameter of water quality involves waste removal. The waste products of fish include carbon dioxide and ammonia. Uneaten feeds also contribute to the total concentration of waste products. If the wastes are allowed to accumulate in the water, serious health problems can ensue. In a pond system there is a natural biofilter composed of algae, zooplankton, bacteria, and higher plants. Like filters in a home aquarium, biofilters remove waste products. The biofilter does more, however, in that it processes the wastes. When pond production becomes too great, the filter loses its effectiveness. At this point, some artificial means of control, such as mechanical aeration and full or partial water changes, is needed to remove the wastes.

Along with water usage in aquaculture there is the accompanying electrical usage. Water in aquaculture is pumped, aerated, filtered, and sometimes heated or cooled. Mr. Brad Powers, Assistant Secretary in the Office of Marketing and Aquaculture Development of the Maryland Department of Agriculture, estimates that utility costs can attain 20% of total costs.(19) In his estimation , this is "very high." Statistics on this point are nonexistent.

Feed

A utility bill of up to 20% of total costs is high, but the greatest expenditure in aquaculture is feed. Feed alone may comprise 40-60% of total expenditures.(20) Feed is extremely important because without a high quality food source, there will be little fish growth, and, thus, little or no profit.

When fish are reared in submerged cages, feed takes on added importance to a successful harvest. Since caged fish are not able to forage for insects and other food sources naturally present in a pond system, the feed must be not only balanced, but also of high quality. It must be palatable to the fish and of appropriate size. It must be offered at a time and in a way which promotes its total consumption so that pond/tank pollution problems will be avoided.

It is known that the manner and type of feeding, as well as the amount and type of feed, all have a profound influence on the growth, size variation, and quality of the fish. Because improper feeding practices may result in higher costs and poorer water quality, the latter of which could lead to disease, feeding management strategies are of the utmost importance to aquaculturists.

A general rule is that fish are fed as much as they will eat in ten minutes, twice per day. Alternatively, they could be fed all that they can eat in 15 minutes, once per day. Food should be offered every day, even during the winter months. At one time, farmers believed that catfish underwent a sort of hibernation during the three coldest months of the year. As a result, they did not feed the fish.(21) Hibernation of catfish is no longer believed to be true.

The aquaculturist who has an effective feeding management program must accompany it with high quality feed so as to ensure a success at harvest. By far, protein is the major component of all high quality fish feeds. For example, channel catfish are usually fed a diet of 32% protein. Trout and salmon eat feeds with protein levels ranging from 40-46%. Species for which a commercial feed has not yet been developed usually are fed trout or salmon diets.(22)

The nutritional requirements of many aquatic species are not well understood. Thus, it is a complex matter to devise commercial feeds containing appropriate amounts of necessary ingredients. The complexity of the task is augmented by the fact that the nutritional requirements of fish change throughout the life cycle. Yet, it is imperative for the health of the fish that the natural diet be approximated as closely as possible. Poor nutrition can result in deaths, slower growth rate, inhibited reproduction, and increased disease susceptibility.

When it is not possible to feed a species a dietary substitute which meets all of its nutritional needs, or if a species requires an exclusively natural diet, aquaculturists must raise components of the natural diet along with their primary commodity.(23) The natural diet might include algae, insects, or minnows.

The production of the natural food is achieved with the application of organic and/or inorganic fertilizer. Organic fertilizers include the following: barnyard and poultry manures, dried hay, and meals containing a high nitrogen content, such as cottonseed or soybean meals.(24) Feeds containing meat scraps, fish meal (derived from fish or fish parts), and feather meal (derived from poultry feathers) may be used to grow the natural diet.(25)

When it is possible to use an artificial diet, aquaculturists prefer commercial fish feeds containing fish meal, considered to be an ingredient of very high quality. It has been estimated that 20-25% of fish meal production by the year 2000 will be for aquafeeds. Extensive research into alternative sources of equally good protein sources at reduced cost is being conducted.(26) The research is becoming essential as feed prices in 1996 were higher than ever before.(27)

Aquaculturists prefer to use artificial feeds because production can be doubled by using them.(28) However, there are consequences. These consequences were of concern in January 1996 at the World Aquaculture Society Annual Conference. One session at the conference dealt with the effects of feed quality and feed management on water quality. It was emphasized that feeds are major contributors to water pollution and nutrient loading of pond effluent. As feed use increases per unit area, the need is even greater for "environmentally friendly feeds" or "low pollution feeds" and "environmental ly friendly feed management strategies." The conclusion of the session was that "the development and implementation of [environmentally friendly feeds and feed management strategies] are critical for aquaculture to meet its responsibility of minimizing environmental pollution."(29) We will return to this subject in Part II of this article. For now, let us turn to another aspect of aquaculture management: health maintenance.

Fish Health

We have already seen how important the source and quality of water and feed are for an aquaculturist to have a successful harvest. Water and feed contribute in major ways to the health of the fish. In fact, under ideal conditions, that is, when water quality is very good and feed quality is very high, farmed fish should develop quickly to market size. However, this is not often the case.

There are many stresses in a fish's life. Many of the stresses are due to common human errors in aquacultural management practice. These include the following: overstocking or understocking of fish per pond/cage; poor quality feed; overfeeding; poor handling of fish.(30) These stresses allow pathogens, (disease-causing agents) to take control. Disease will occur when three conditions are satisfied: (1) presence of a pathogen; (2) compromised immunity/health of the fish; and (3) deteriorated living environment.(31) Let us look more closely at these points.

Pathogens are normally present in the living environments of fish. Typically, the pathogens are present in small numbers and co-exist with the fish without causing illness or disease. However, when the fish are stressed, their ability to resist the pathogens is reduced.

Fish can become stressed for many different reasons, as indicated above. Poor water quality is sufficient reason. At the very least, poor water quality could augment existing disease, resulting in death. Unfortunately, it is difficult to determine if fish are stressed, or to identify the source(s) of stress. Often, the determination is made after the disease has established itself or even after the fish have died.

Fish often hide from people, making it difficult to correctly diagnose the stress. Attempts to catch a sample of live fish for observation is in itself a stressor which could produce illness or augment existing disease. Feeding is the ideal time to observe fish; changes in behavior and/or appearance are often indicative of problems. For example, a reduction in feed consumption could indicate disease, low dissolved oxygen level, or poor quality water. Skin discoloration, spots, fin erosion, or erratic swimming are usually signs of disease or parasites.(32)

Once the disease has been identified, the fish are medically treated. This treatment may take many forms, depending on the pathogen. If, for example, the pathogen is an internal bacterial disease, the treatment may be a medicated feed. If an external bacteria or parasite is the problem, water treatment is often necessary.(33)

When therapeutants are called for, the aquaculturist does not have many choices. In fact, there are only five FDA-approved drugs in aquaculture.(34) However, there are several substances commonly used in aquaculture which have never been properly registered. They are known as "low regulatory priority drugs."(35)

Tifa Limited, a supplier to aquaculture of Rotenone-containing compounds, reports that Rotenone is a restricted-use pesticide due to its aquatic toxicity. Their compounds are "used extensively in the aquaculture arena to eliminate predators in competitive species."(37) Their products are sold with the following precautionary statement: "May be fatal if inhaled or swallowed."

Lastly, there are several herbicides used in commercial fish production ponds. They kill various types of plant life. It is known that the application of excessive amounts of herbicides does not increase the level of weed control although it may increase the risk of injury to fish.(38)

Aquaculturists hope that treating the water with any of the listed drugs will help to control the level of disease-causing agents so that the species being raised will not succumb to illness or death. In most cases water treatment is sufficient to control and/or contain the problem. However, if a disease is very serious, aquaculturists may try a more aggressive course of action by using therapeutants.

Treating fish disease is not an easy task. First of all, there are four very different types of fish pathogens: bacteria, viruses, fungi, and parasites. Because of their different natures, each pathogen must be combated differently. Let us consider each pathogen individually.

Bacteria

Bacteria quickly develop resistance to frequently-used antibiotics. For example, a type of bacteria is the usual causative agent of a disease called Motile Aeromonad Septicemia (MAS), one of the most common diseases of cultured channel catfish. In the late sixties-early seventies, only 10-15% of these bacteria from infected catfish were resistant to antibiotics; by 1976, 38% were resistant. Now, the percentage approaches 50%.(39)

The problem of antibiotic-resistant bacteria is a very serious one. Without a defense, bacteria can easily get out of control. This happened in the case of enteric septicemia, an economically devastating disease of catfish caused by a highly infectious bacteria which spread to many far-reaching places in the U.S. in less than two decades, creating fish die-offs in many states.(40)

Virus

There are also viral diseases of fish. A notable case is the taura virus, a virus which affects shrimp. This virus spread throughout Ecuador, into Central America and Hawaii, and recently reached Texas, all within three years. In May 1995, mortality rates at infected shrimp farms reached 80-90%.(41) Another virus, widespread in the U.S., is responsible for channel catfish virus disease (CCVD).(42) Loss of fingerlings (young fish) to CCVD at aquaculture farms may exceed 80%. As with all viral diseases, there is no known cure.

Fungi

Thirdly, fungi may be responsible for fish diseases. Fungi grow on organic matter or dead eggs and can cause widespread infection in a pond/tank.(43) Scrupulous sanitation is requisite for avoiding outbreaks. Sometimes, fish are treated with potassium permanganate, formalin, or salt. However, these treatments do not totally eradicate the fungi. Thus, the fungi simply reinfect the fish unless the stress-causing condition is removed.(44) A common fungal disease is known as saprolegniosis.(45)

Parasites

Fish are also prey to parasitical diseases. Salmon lice is one example of worldwide, economic scale.(46) Dermo, which has caused high mortalities of the Eastern oyster, is also a parasite.(47)

These four types of pathogens noted above occur in wild populations. The pathogens' harm to a wild fish population is usually not serious because of the fishs' relatively good state of health and of their environment. However, in an artificially-controlled setting where fish density is high, pathogens easily spread in a fish population. High mortality rates lead to great economic losses for aquaculture. As a result, scientific research is currently underway to help reverse this state of affairs.

Current Scientific Research

Researchers at the Aquaculture Research Center at the University of Maryland Center of Marine Biotechnology in Baltimore, Maryland, are developing the technology which is intended for use in the aquaculture industry. Several studies focus on the induction of year-round spawning (i.e., the laying of eggs); the development of new lines of commercially farmed fish; the regulation of the growth and development of fish; and the development of vaccines and drug-delivery systems.(48) Other studies seek to identify genes which control disease resistance and resistance to extreme environmental conditions.(49)

Research on the induction of year-round spawning was called for when it became evident that captive fish often fail to spawn, or spawn in an unpredictab le manner. The cause of the problem is due to the failure of a gland to release the hormone that triggers spawning. Researchers are able to induce hormonal release, and the consequent spawning, by the injection of another hormone which in turn releases the target hormone. Currently, AquaPharm Technologies, a Maryland company, is perfecting this technique so that the aquaculture industry can benefit.(50)

Researchers at the Aquaculture Research Center are also investigating the effect of light and temperature on the timing of both sexual development and spawning. Their objective is to provide aquaculture with a year-round, plentiful supply of eggs and fry (newly born fish).(51)

Related to the previous investigation is a study which aims to develop hormone therapies that accelerate sexual maturation in bass. The acceleration of sexual maturity should reduce the cost to aquaculture of maintaining breeding fish.(52) Hormonal controls are also being developed to achieve sex reversals in order to convert all the members of a population to the faster-growing sex.(53) Such programs for salmonids are growing in popularity in the U.S. All-female populations are already used in the United Kingdom.(54) There are several projects which strive to maximize growth rates of commercial species. One project has successfully isolated growth hormones which were produced on a large scale through recombinant DNA technology.(55) In this technology, genes, the "blueprint" of all life, are recombined. The organisms which possess these genes exhibit new traits. Another project has successfully introduced genes for fish hormones into other species of fish. The result was the production of fish known as transgenic. These fish show a growth enhancement of at least 50%.(56)

It has also been reported that several fish species, such as the common carp, channel catfish, and northern pike, which possess genes from human, bovine, or salmonid sources, show 10-80% faster growth rates than their non-transgenic counterparts under certain conditions.(57) With such growth enhancement, the time needed to raise fish to market size would be greatly reduced. Fish farmers could also increase production with this technique. Gene technology may also be employed to create disease resistance in fish species. This has already been accomplished in the case of the Eastern oyster with respect to its resistance to a parasite known as MSX.(58) Scientists hope that this technology will be expanded to other aquaculture species and applied to other diseases.

Gene technology is not new, only newer. Aquaculturists have been genetic engineers ever since they began domesticating fish. They selectively bred certain fish in order to produce certain desirable traits. The commercial species of today are the prized commodities of years of this type of selective breeding. With the advent of recombinant DNA, the selective breeding will take on a new look, and, most likely, a faster pace. The goals of aquaculturists will continue to be centered on creating commercial species with an increased growth rate, improved disease resistance, and earlier sexual maturity. Also gaining in popularity is cross-breeding fish from different species. The objective is to produce faster-growing fish, or fish which manifest such traits as greater flesh quality or increased tolerance of low dissolved oxygen. One example of this type of breeding is the cross produced by female channel catfish and male blue catfish. Commercial production of the hybrid could increase gross earnings by $150 million.(59)

Aquaculturists also breed polyploid fish. Polyploids are fish with three, four, or more copies of a given gene, rather than the normal two. A fish called a triploid possesses three copies of a given gene. This fish is sterile. Triploid fish of exotic species could be used for aquatic weed control instead of their genetically normal counterparts. Using the triploids eliminates the risk of accidental, and illegal, reproduction of the species in the wild. Furthermore, any concern about an accidental release of diploid exotics could be circumvented through sex reversal and the subsequent breeding of single-sex populations.(60)

Author's Analysis

Given the fact that aquaculture is a part of our economy and is a growing industry on the verge of much proliferation and sophistication due to scientific research, what may we say about aquaculture from the ethical and environmental points of view? Based on the facts presented here, we may make several conclusions.

We have seen that aquaculture uses a large amount of water and energy. Aquaculture acknowledges this fact insofar as it is implementing water recirculation systems. Due to a real need, aquaculture must look for a water management plan which takes less of a toll on the environment than much of the current system which relies heavily on ground water or running river water. Because of the necessity, we can predict that one day aquaculture will largely consist of water recirculation systems which are efficient in terms of the quantity of water used. Along with a restriction on the quantity of water used will arise more energy-efficient filtration and aeration systems. This will be a necessity in order to keep the water clean for high-density fish raising.

Aquaculture also uses a large amount of feed. The preferred feed in fish farming is itself fish and/or fish products such as bones and waste matter. >From a strictly ecological point of view and insofar as the feed used in aquaculture is made of aquacultural wastes, aquaculture is to be commended for its recycling of its wastes back into its own production system. Other large components of the feed are soybean meal and wheat middlings (coarsely ground wheat mixed with bran).

On a pound by pound basis, more fish is produced per pound of feed than is beef, pork, or chicken. On this point, we may conclude that aquaculture is more efficient than the other forms of animal agriculture. However, the question remains whether aquaculture feeds people more efficiently than purely plant-based systems.

What may we conclude about the ethical and environmental aspects of fish health issues? First of all, we cannot say that intensive aquaculture is "bad" because fish densities are high. In fact, when fish density is low, stress may result simply because of this fact. The territorial drive of fish can be easily manifested in such low-density situations and result in aggression toward other fish. This is not the case in high-density situations where, in schooling species at least, the drive to school is met. However, if the density of fish is very high, overcrowding could create and/or augment stress. The stress could, in turn, create and/or augment disease, which could result in fish die-offs.

While granting that disease exists in natural systems, the fact that disease exists in aquaculture is evidence that stress is present in aquacultural systems. Too much stress means economic loss for aquaculturists. It is in aquaculture's best interest to minimize stress as much as possible. If not, disastrous events could occur, such as increases in bacterias' resistance to antibiotics, the major line of defense against bacteria. Without antibiotics, bacterial infections could rapidly get out of control, spreading to wild populations as well. Aquaculture needs to make sure that this does not happen.

How aquaculture is making sure that this does not happen needs commentary. Does the answer lie in the development of stronger antibiotics or in the genetic engineering of fish which are more resistant to disease? Or does the answer lie in the remaking of aquaculture so that the stresses which lead to disease would be eliminated? Is it desirable that aquaculture use genetic engineering in order to produce fish with faster growth rates, earlier sexual maturity, and year-round ability to reproduce?

These are difficult questions which demand careful consideration beyond the scope of this article. The author hopes that with this article, readers have adequate information with which to make their own assessments and draw their own conclusions about aquaculture.

References


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