20.1 OXYGEN REMENTS IN STATIC CULTURE SYSTEMS

Parker, Nick C. (Texas Cooperative Fish and Wildlife Research Unit) Texas Tech University, Lubbock, TX 79409-2125

In aquaculture facilities intensively stocked pith fish, dissolved oxygen typically becomes the first factor limiting growth and production. Oxygen is required not only for respiration by the fish cultured but also by the resident macro and micro invertebrate species- including crayfish, aquatic insects, zooplankton, and bacteria-phytoplankton and non-emergent aquatic plants, and to meet the chemical oxygen demand of organic and inorganic compounds. Metabolic rate and oxygen consumption (milligrams of oxygen per kilogram of body weight) of aquatic organisms is inversely related to size and directly related to temperature, concentration of dissolved oxygen, time since last feeding, and locomotor activity. Although gradual decreases in dissolved oxygen may not be stressful to fish, they adjust to low levels of oxygen by inducing feeding and growth, Abrupt decreases in dissolved oxygen induce stress and subsequently make fish more susceptible to disease. Saturated or supersaturated concentrations of oxygen promote greater feed consumption, growth, and reduce the likelihood of disease. Dissolved oxygen in static outdoor culture systems fluctuates daily as a result of photosynthesis and wind action. Management options to provide the necessary oxygen in static culture systems include (1) reduction of stocking density, (2) providing mechanical aeration. (3) controlling algal blooms. (4) reducing nutrient input, and (5) direct injection of gaseous oxygen.


20.2 AERATION NEEDS AND AERATING DEVICES

Boyd, Claude E. Department of Fisheries and Allied Aquacultures, Auburn University. AL 36849

Aeration may be used in static ponds on an emergency nighttime, or continuous basis. At moderate stocking densities and feeding rates (30 to 90 kg feed/ha per day) nighttime aeration for 6 to 8 hours per night appears more efficient than emergency aeration. At high stocking densities and feeding rates (above 90 kg/feed/ha per day) continuous aeration ma), be needed. At high aeration rates, high concentrations of nitrogenous metabolizes rather than low concentrations of dissolved oxygen often limit production. Many different types of aeration devices are available for use in ponds. The most common devices are: vertical, pump-sprayer aerators; propeller-aspirator-pump aerators; high pressure, pump sprayer aerators; diffused air systems; and paddle wheel aerators. Successful results have been achieved with all of these types of aeration devices, but some types are more suitable for a particular situation than other types. The basic features of these aeration systems will be discussed. Water circulation also is important in static ponds. Air-lift pumps and low head, low velocity pumps may be used to circulate pond water. These devices provide little mechanical oxygen transfer as compared to aerators.


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