Objectives: The student will be able to:
Time Requirement: 1-3 weeks
Tools and Materials: Water quality testing kits (to be shared).
Suggested but not required for this lesson:
FAQs
Question – What is the fastest growing food industry of the future?
Answer – Aquaculture. As our natural fishing areas are depleted due to over-fishing and the demand for more seafood products, aquaculture will become an increasingly valuable renewable source of protein in the future.
Question – Are fish grown by farmers?
Answer – Yes, when we speak of food production, we can't forget about animals like fish. Growing fish is called aquaculture (“Aqua” meaning water). Today, most aquaculture is in outdoor ponds. In the future people will depend more and more on this kind of farming.
History:
Aquaculture is not a new industry. Asian and European fish culture systems have existed for centuries. Although aquaculture is a large and growing industry over much of the world, it is relatively new and undeveloped in the United States. United States production contributes only about 2% of worldwide aquaculture production. In 1975 U.S. production reached 65,000 metric tons with proper support it should reach 1 million tons by year 2000 (National Research Council, 1978). Private aquaculture produces over 40% of U.S. oysters, most U.S. catfish and crawfish, nearly all rainbow trout, and small quantities of several other species.
The outlook of the U.S. aquaculture industry is encouraging for several reasons:
Individual aqua-culturists or persons thinking of entering into this business must carefully consider all of the elements needed for profitable aquaculture. Available natural resources must be appropriate for the species to be cultured. The aquaculture facilities and operations must conform to a wide variety of regulations often involving permits. The products must be economically grown and effectively marketed and of course, the life cycles of the desired species must be subject to an adequate amount of control under practical aquaculture conditions.
Ponds used for aquaculture can be either natural or man made with surface areas from less than 1/10 acre to greater than 10 acres. Man made ponds include dug out and impounded waters, lime rock pits, and sand or gravel pits, commonly called burro pits.
Selection of Species:
Selection of species used for aqua-farming is important and can determine the success or failure of an operation. Here are a few species that have potential as aquaculture organisms (this is not a comprehensive listing).
Water Quality:
Water, although the most important component for raising fish is often the most neglected factor. Fish are totally dependant on water:
Poor water quality can cause massive fish kills and is often the major factor contributing to fish diseases.
Q – Instead of adding chemicals to the water to treat a disease outbreak, the fish culturist should do what?
A – The fish culturist should first look at water quality to determine why the outbreak occurred.
Q – Does water quality remain the same?
A – No, it can change dramatically over a few hours. Even water from the deep wells and springs can change over time. It is a simple matter for the fish farmer or pond owner to assess water quality. The fisheries manager must use chemical tests as well as observations to detect changes. (Standard instruments and kits for measuring water quality are available through commercial suppliers.)
The most important water quality characteristics include:
Dissolved oxygen:
As I mentioned earlier, Tilapia have the ability to withstand low dissolved oxygen levels. Dissolved oxygen is by far the most important water quality factor for fish; fish cannot live without it, and oxygen depletion probably results in more fish kills than all other factors combined. Concentrations of oxygen are expressed as parts per million (ppm) by weight or milligrams/liter. The amount of oxygen, as well as many other gases that can be dissolved in water, decreases with higher temperature. At 68* F water can hold 8.8ppm oxygen, while at 90*F, saturation is at 7.3ppm. In combining this relationship with the increased demand for oxygen by fish and other organisms at higher temperatures, you can easily see why summer oxygen depletion is so common. Fish farmers, in an attempt to maximize production, stock a greater biomass of fish in a given body of water than found in nature.
Q - What happens when the farmer stocks more fish in a pond than found in nature? (allow for discussion)
A - There is a greater demand for oxygen by the fish in the pond..
Q – Is the oxygen requirement the same for all fish?
A – No, it will vary according to species, age, and culture conditions. Most warm water fish require a minimum of 1ppm to survive and more than 4ppm for growth, reproduction, and good health. Early life stages usually require greater oxygen concentration than needed by adults. Low dissolved oxygen causes stress to fish and therefore increases the chance of infectious diseases. Fish, insects, bacteria, and aquatic plants all consume oxygen in a pond. While plants are oxygen producers during the day, at night they become oxygen consumers.
Temperature:
Temperature has a direct effect on fish metabolism, feeding, and survival. No other physical factor affects the development and growth of fish as much as water temperature. Metabolic rates of fish increase rapidly as temperature goes up. Conversely, as temperature decreases, so does the fish's demand for oxygen and food. Many biological processes such as spawning (eggs of fishes) and egg hatching are geared to annual changes in environmental temperature. Did you know that each species of fish has a temperature range that it can tolerate; within that range, there is an optimum temperature for growth and reproduction, which may change as the fish grows? Like fish, diseased organisms also have an optimum temperature range for development, and out-breaks are more prevalent during these kinds of conditions.
Large, rapid changes in temperature are stressful to fish and may result in death.
pH:
The standard measure of acidity of pH, the logarithm of the reciprocal of the hydrogen ion concentration. As you probably remember, the pH scale ranges from 1 to 14; the lower the number, the greater the acidity, with 7 being neutral. Fish are able to live in waters within a pH range of about 3.5 to 10, but the desirable range for most fish is generally considered to be 6.5 to 9. However, most tropical fish species require acid waters for breeding and larval development. Fish have less tolerance of pH extremes at higher temperatures. Ammonia toxicity becomes an important consideration at high pH and hydrogen sulfide is more toxic at a lower pH.
The pH of pond water is influenced by the amount of carbon dioxide present. Much of the CO 2 present is the result of animal and plant respiration. Carbon dioxide is utilized during photosynthesis; therefore, CO 2 concentrations in water increase at night and decrease during daylight hours. Since CO 2 in water is an acidic substance, the pH of water is usually highest in the late afternoon and lowest just before sunrise.
Accurate measurements of pond water pH are best determined on site. The pH of water many change during the interval between sampling and determination in the laboratory. (Various companies manufacture field test kits and meters for measuring pH). For an accurate measurement of daily changes in pH, pond water should be sampled during early morning and late afternoon hours.
Alkalinity and Hardness:
Alkalinity and hardness are similar but they represent different types of measurements. Alkalinity refers to the capacity of the water to accept hydrogen ions and is the direct counterpart of acidity. The anions (negatively charged) or bases involved are mainly carbonate (CO 3 2-), bicarbonate (HCO 3-), and hydroxide ( OH-); alkalinity refers to these in terms of equivalent concentrations of calcium carbonate. Originally, the hardness of any water was the measure of the capacity of the water for precipitating soap. Soap is precipitated chiefly by calcium and magnesium ions, but may also be precipitated by divalent ions of other metals, such as aluminum, iron, manganese, strontium, and zinc, and by hydrogen ions. When the hardness is numerically greater than the sum of the carbonate and bicarbonate alkalinity is called “carbonate hardness;” the amount of hardness in excess of this is called “noncarbonated hardness.” Hardness, like alkalinity, is also expressed as CaCO 3 equivalent concentration. Many people incorrectly use the term “hard water” to refer to water with high alkalinity. Most waters of high alkalinity are hard waters, but this is not always true. Fish culturists often place undue emphasis on the total hardness of water. Total hardness is usually not nearly as important as total alkalinity in pond fish culture.
Fish grow over a wide range of alkalinity and hardness. Natural waters that contain 40 mg/l or more total alkalinity are considered more productive than waters of lower alkalinity. The greater productivity does not result directly from alkalinity, but rather from phosphorus and other nutrients that increase along with total alkalinity. In fertilized fishponds, total alkalinity values in the range of 20 – 120 mg/l have little effect on fish production. However, in fertilized ponds containing less than 20 mg/l total alkalinity, fish production tends to increase with increasing alkalinity. At low alkalinity, water may lose much of its ability to buffer against changes in acidity, and pH may fluctuate. Even when alkalinity is zero, if weak acids such as tannic acids are present, they may accept hydrogen ions, thereby buffering changes in pH. Fish may also be more sensitive to some toxic substances such as copper at low alkalinity. Many tropical species, however, require low alkalinity and soft water for survival of the eggs and larvae.
Determination of water hardness and alkalinity can be made on site either with water test kits or by submitting a sample for analysis to a laboratory. Agricultural (dolomitic) lime is recommended for increasing alkalinity and it is difficult to over lime a pond.
Health Problems:
Before you can recognize a fish health problem, it is necessary to recognize healthy fish. Observe their feeding habits. Voracious? Timid? Selective? Piggish? Are they active in the day? Passive? Do you know what a healthy fish looks like? Look at the gills and observe the healthy red color and texture of the gill tissue. Look at the skin and scales, and feel the slickness of the slime layer. Make a mental note of healthy fish characteristics to use as a future reference for identifying problems. When normal behavior and appearance are known, then abnormalities can be recognized as an indication of a fish health problem. Some common behavioral indications of a fish health problem are:
When abnormal behavior is observed, it is necessary to capture some of the suspect fish for closer examination. Look at live fish when examining a health problem. Dead fish will decompose quickly, obscuring physical clues of the cause of death. Some problems will be very obvious, such as open sores on the body, missing scales and/or lack of slime, and strange growths on the body, head or fins. Other problems are not so obvious and are difficult to diagnose without a microscope.
There is no single treatment that will cure all fish diseases and parasite problems so it is necessary to diagnose the problem by treatment category. There are several philosophies of treatment:
A decision to treat a fish health problem should be based on the extent of the problem and the economics of the situation. Some fish mortality or weak fish in a population are common and should be expected. It is only when the incidence of mortality or sickness increases to an unacceptable level that treatment should be considered.
Review:
As our natural fishing areas lose their fish populations, aquaculture will become more important as a source of animal protein in the future. Today most aquaculture is conducted in outdoor ponds, but in the near future farmers may use closed tanks, which recirculate water for better conservation. Since fish are very dependent on water, water quality is critical.
As with any type of agriculture, it is essential to select the proper species for the environment. The species must enjoy crowded places, since the object is to produce the largest possible harvest in the smallest amount of space.
Through good water quality management and proper fish husbandry techniques, most health problems will be eliminated.