Английский язык: Сборник текстов и упражнений. Дьякова Н.П. - 74 стр.

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   IV. Translate into Russian using a dictionary.
                        Management of Culture System
    Once the species for culture has been selected and the culture system has been
constructed and stocked, aquaculturists must address various management con-
cerns. In terms of things that should be monitored by the aquaculturists, perhaps
the most important water quality variables are temperature, dissolved oxygen and
ammonia. Other variables can be important under certain circumstances, but the
three mentioned generally provide a good indication of the performance of the an-
imals in the culture system.
    Temperature:
    Aquaculture species are all «cold-blooded» or poikilothermic. That means that
their body temperatures are virtually the same as the temperature of the water that
surrounds them. Basically, there are two primary types of culture species with re-
spect to temperature: warm water species and cold water species. Carps, tilapia,
channel catfish and freshwater shrimp are examples of warm water species. Trout,
salmon and American lobsters are examples of cold water species. The optimum
temperature for warm-water species tends to be about 86°F (30°С), while that for
coldwater species is often 59°F (15°C). Some species of aquaculture interest, such
as the yellow perch, have temperature optima between the warm and coldwater
species and are known as mid range species. Few mid-range species are currently
being cultured.
    When temperature changes dramatically, and in particular, when it moves out
of the optimum range, aquaticanimals are placed under strees. It is at such times
that disease resistance is lowered and problems often arise. Knowledge of the
temperature requirements of the species under culture and of the temperature at
any given time will not only provide the culturist with valuable information about
how well the animals are growing and how much to feed them, it will help to es-
tablish the disease resistance status of the animals.
    Dissolved Oxygen:
    Oxygen enters water by dissolution from the atmosphere and through the re-
lease of that element by plants during photosynthesis. Animals with gills respire
by absorbing oxygen that has been dissolved in water directly into the blood
steam through diffusion as a general rule, if the water contains 5 parts per millon
(ppm or mgll) of oxygen, it will support aquatic organisms. Some fish, such as ti-
lapia, can survive at very low concentration of oxygen, while others, such as trout,
are stressed if the concentration falls below 5 ppm.
    Daily changes in temperature are very small relative to the changes that can
occur seasonally, particularly in temperature climates. Daily changes in dissolved
oxygen, on the other hand, can be substantial. Dissolved oxygen begins to in-
crease at about dawn, when photosynthetic production of oxygen by the plant
community begins. As the sun rises, photosynthetic oxygen production increases
with the increasing amount of light energy available. While both plants and ani-
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