Dynamics of Pond Aquaculture

Hillary S. Egna, Claude E. Boyd

• Verlag: CRC Press
• Jahr: 2017
• ISBN:
  9781351454063
• Auflage: 1
• Thema: Scienze biologiche
• Thema: Biologia marina

The culmination of over a decade's worth of research by the Pond Dynamics/Aquaculture Collaborative Research Support Program (CRSP), Dynamics of Pond Aquaculture not only explains the physical, chemical, and biological processes that interact in pond culture systems, but also presents real-world research findings and considers the people who depend on these systems. This book uses data from CRSP field research sites in East Africa, Southeast Asia, Central America, and North America to present a complete picture of the pond system and the environment in which it exists.
A thorough study of the principles and practices of aquaculture, the book reflects the state of the art in pond aquaculture and incorporates recent advances that have changed the science in the last decade or so. It provides a thorough review of the many methods, techniques, and ideas that comprise this complex and fascinating area of study.

1	INTRODUCTION

Hillary S. Egna, Claude E. Boyd, and Deborah A. Burke

Aquaculture is the cultivation of aquatic animals and plants. Its primary purpose is to produce aquatic food organisms for human consumption, but includes other purposes such as the cultivation of ornamental and aquarium fishes. Aquaculture may be done on many scales, ranging from small rainfed ponds to increase food production for rural families to large commercial farms to provide export products for international markets. Regardless of scale, aquaculture is an economic activity, and the value of aquacultural crops must exceed the cost of producing them. Knowledge of factors and interactions that determine success in aquaculture is not as well developed as in traditional agriculture; thus, aquaculture has tended to be risky and has suffered in some instances from unsustainability. But aquaculture technology is improving rapidly, and more reliable production systems are emerging.

Most aquaculture involves cultivating a species of interest under conditions that can be monitored and controlled. Sessile creatures such as mollusks can be cultivated by providing substrate for their attachment. However, fish, crustaceans, and other motile organisms are usually confined in order to cultivate them. The most common confinements used in aquaculture are ponds, raceways, cages, and pens. Ponds are by far the most widely used means of confining warmwater fish and crustaceans for cultivation. Therefore, it was quite appropriate for the U.S. Agency for International Development (USAID) to initiate a project on pond aquaculture as a Collaborative Research Support Program (CRSP). The purpose of this book is to summarize advances in pond aquaculture that have accrued from the CRSP effort. The intent of this introductory chapter is to summarize the role of aquaculture in world fisheries and to explain why research and development in the area of pond dynamics are critical to the sustainable development of aquaculture.

POND AQUACULTURE

The Role of Pond Aquaculture

According to FAO (1995), the total capture fisheries of the world peaked at about 90 million metric tons in 1989. Capture fisheries have provided around 85 million metric tons per annum since 1989. Aquaculture has been very important in supplementing capture fisheries. Since 1984, aquaculture has grown at annual rates of 8 to 14%, with an 89% increase in production between 1984 and 1992 (Anonymous, 1995). The total production of aquaculture was estimated at 19.3 million metric tons in 1992. Because of the contributions of aquaculture, world fisheries production has remained slightly above 100 million metric tons per year since 1988, despite the fact that capture fisheries peaked in 1989 and declined slightly in the following years (FAO, 1995).

In 1992, aquaculture produced 18.5% of the global fisheries output. Thirty-five countries produced 98% of the aquaculture products in 1992 (Anonymous, 1995). Of the total production of 19.2 million metric tons, 17 million metric tons were produced in Asia. In terms of total production, carps and other cyprinid fishes represented the greatest production of aquaculture products, with about 6.7 million metric tons. Other major contributors were tilapia and other cichlids, miscellaneous freshwater fishes, oysters, mussels, scallops, marine shrimp, trout and salmon, and seaweeds. Marine shrimp had a remarkably high monetary value, in spite of their relatively low contribution to total production.

Freshwater fish culture is particularly impressive in its contribution to the total freshwater fisheries production of the world. The production of freshwater aquaculture in 1992 was 8 million metric tons (FAO, 1995); this was 61% of the total freshwater fisheries output. Marine and brackish water aquaculture contributed 39.4% of the world mollusk production in 1992, and 25% of the world shrimp production in 1994, but it produced only 5.9% of seaweeds and 0.5% of fish in 1992.

It is not certain what percentage of total aquacultural production comes from ponds, but it is thought to be more than 50% of the total. Of course, if only fish and crustaceans are considered, well over 75% of total production is from ponds. Clearly, ponds are very important aquaculture production units.

Types of Pond Aquaculture

We may classify pond aquaculture along several lines, such as species, pond characteristics, and intensity of culture. In attempting to list all aquaculture species, Pillay (1990) named 95 finfish, 32 crustaceans, 35 mollusks, and 19 aquatic plants commonly used in aquaculture. Avault (1996) mentioned more than 100 aquaculture species in his discussion. More than 400 aquaculture species were listed by Jhingran and Gopalakrishnam (1974). Therefore, a classification of aquaculture by species would be unwieldy.

Culture techniques usually do not differ greatly for aquaculture products of similar characteristics. Thus, it is popular to speak of the culture of sport fish, food fish, ornamental fish, crustaceans, mollusks, frogs and other amphibians, alligators and other reptiles, vascular aquatic plants, seaweeds, etc. It also is useful to divide the culture categories according to temperature preference, i.e., coldwater, coolwater, warmwater, and tropical, and according to salinity preference, i.e., freshwater, brackish water, and marine.

The culture systems may be classified by type of grow-out units, i.e., ponds, cages, pens, raceways, tanks, silos, etc. This book emphasizes primarily pond culture. Ponds may be classified according to construction methods as watershed ponds, excavated ponds, and levee ponds (Yoo and Boyd, 1994; also see Chapter 5 for other pond types). Watershed ponds are formed by building a dam across a natural watercourse where topography permits water storage behind the dam. The dam is usually constructed between two hills that constrict the watershed. Watershed ponds may store only overland flow, or they may receive some combination of overland flow, stream flow, and groundwater inflow. Excavated ponds are formed by digging a hole in the ground. They may be filled by groundwater inflow where the water table is near the land surface, by overland flow if constructed in a low-lying area, or by well water. The water in levee ponds is impounded in an area surrounded by levees. Little runoff enters levee ponds, so they must be filled by water from wells, storage reservoirs, streams, or estuaries. Hydrologically, ponds may be classified in various ways — for example, as static ponds with little water exchange or as flow-through ponds where water exchange is used on a regular basis.

From the standpoint of pond dynamics, the most meaningful classification of ponds is the intensity of management inputs and the amount of production. In extensive aquaculture, there are few inputs of nutrients, and production is quite low. Larger nutrient inputs are provided and greater production is obtained in semi-intensive aquaculture. The greatest inputs of nutrients are provided in intensive aquaculture to achieve very high production. An attempt has been made in Table 1 to summarize the different levels of management and amounts of net production that are typical in the culture of marine shrimp, tilapia, and channel catfish. There are no standard definitions of extensive, semi-intensive, and intensive aquaculture, but reasonable divisions between the three levels of management are as follows:

Table 1 Representative Net Production (kg/ha) for Channel Catfish, Tilapia, and Marine Shrimp with Different Levels of Management

Management	Channel catfish	Tilapia	Marine shrimp
Stocking only	50–100	200–500	100–200
Stocking and fertilization	200–300	1,000–3,000	400–600
Stocking and feeding	1,500–2,500	3,000–6,000	—
Stocking, feeding, and water exchange	—	—	1,000–2,000
Stocking, feeding, and aeration	2,500–5,000	6,000–10,000	—
Stocking, feeding, aeration, and water exchange	5,000–10,000	10,000–20,000	3,000–10,000

Extensive — production is enhanced only by manures or chemical fertilizers

Semi-intensive — feeds are used to increase production; manures and chemical fertilizers also may be used

Intensive — large amounts of feed are applied, manures and fertilizers may be used, and ponds are aerated by mechanical means

Water exchange is uncommon in freshwater pond aquaculture, but it may be used in very intensive systems. In brakishwater pond aquaculture, water exchange is used commonly at all levels of production. Water exchange rates are greatest in intensive, brakishwater aquaculture. As aquaculture gains momentum throughout the world, more and more farmers are leaning toward higher production strategies through increased intensification. For example, in rural, subsistence aquaculture, more farmers are beginning to use chemical fertilizers instead of manures and other organic fertilizers. In commercial aquaculture, there is a rapidly growing dependence upon feeds and mechanical aeration. Production is increasing in both subsistence and commercial aquaculture, but in developing countries, extensive and semi-intensive production techniques are still more common than intensive methods.

Pond Dynamics

The term pond dynamics was used by the CRSP to convey the physical, chemical, and biological factors that interact in pond systems. In pond aquaculture, ponds are constructed, filled with water, and stocked with fish, crustaceans, or other aquatic plants and animals. The amount of production in ponds depends heavily upon the quantity of food available to the culture organisms. In systems without supplemental feeding, primary productivity forms the base of the food web that culminates in fish and crustacean biomass. Natural levels of primary productivity are seldom high enough to provide sufficient natural food for high rates of aquacultural production. Some ponds have more nutrients in their bottom soils and waters than other ponds, and there is a large range in the natural productivity of ponds (Boyd, 1990). In order to enhance natural productivity, manures or chemical fertilizers are applied to stimulate primary productivity. Where watershed and pond soils are acidic, pond waters usually have low total alkalinity, and the response to fertilizers and manures will not be great. Such ponds are treated with liming materials to reduce acidity, increase total alkalinity, and enhance the response to fertilization. The amount of fertilizer or manure used in aquaculture ponds is highly variable, depending upon the resources and desires of the pond manager. Fertilization and manuring can result in 5- to 10-fold increases in fish production over natural productivity if the availability of phosphorus, nitrogen, and other limiting nutrients is increased to a sufficient level. Greater increases in production can be achieved through the use of manufactured feeds to supplement the availability of natural food organisms. Feeds also contain inorganic plant nutrients, and feed wastes fertilize the water to stimulate the primary productivity of ponds.

As the intensity of aquaculture is increased through the application of manures, fertilizers, and feeds, nutrient concentrations increase, plankton blooms occur, and dead organic matter settles to pond bottoms. Although phytoplankton produces dissolved oxygen through photosynthesis in the daytime, respiration also increases as the biomass of pond biota increases in response to nutrient inputs. This results in fluctuations in dissolved oxygen concentrations over a 24-h period, with highest concentrations in the afternoon and lowest concentrations at dawn. If phytoplankton abundance becomes too great, nighttime depletion of dissolved oxygen may stress or kill culture species. Accumulation of organic matter on pond bottoms can result in anaerobic conditions and the release of microbial metabolites, such as nitrite and hydrogen sulfide, into the water column. These substances are toxic to aquatic animals.

The major nitrogenous waste product of aquaculture species is ammonia, and as the intensity of production increases, ammonia concentrations may reach toxic levels. However, low concentration of dissolved oxygen is usually the first limiting factor that restricts production in ponds. If mechanical aeration is provided to enhance dissolved oxygen concentration, production can be increased until ammonia toxicity begins to limit production. The most reliable means of reducing ammonia concentration is water exchange. By exchanging water to flush ammonia from ponds, production levels may be increased. Production cannot be increased without limit through aeration and water exchange, because microbial decomposition of accumulated organic matter on pond bottoms will result in deterioration of bottom soil condition and high concentrations of toxic metabolites.

The discussion above reveals that many complex ecological factors and interactions are involved in the grow-out of aquaculture species in ponds. Aquacultural projects are even more complex, because they are conducted in a multiple-use environment where people live. Also, the value of aquaculture products must be greater than the cost of their production, and the value must be realized though direct use or by marketing. Thus, in addition to the ecological factors at play in aquaculture, many complex socioeconomic factors also are involved.

Tilapia Culture

Several species of tilapia are cultured in the world; this group of fishes is growing in importance both as a species for domestic consumption and for export. Es...