2020-10-10
206
Text C
It is interesting to know
Types of Fish Culture based on species number: Monoculture and Polyculture
| Graze v | [ɡreɪz] | пасти |
| Synergism n | синергизм, взаимное усиление действия | |
| artificial adj | [ɑːtɪˈfɪʃ(ə)l] | искусственный |
| trout n | [traʊt] | форель |
| tilapia n | тилапия | |
| catfish n | [ˈkatfɪʃ] | сом |
| mullet n | [ˈmʌlɪt] | кефаль |
| trophic adj | [ˈtrəʊfɪk] | трофический |
| fertilization n | [ˌfəːtɪlʌɪˈzeɪʃ(ə)n] | удобрение |
| tank n | [tæŋk] | водоём; резервуар |
| harvest n | [ˈhɑːvɪst] | урожай |
Exercise 39. Read and translate the following words and word combinations from English into Russian. Running water system, recirculating, trout, tilapia, catfish, intensive system, a dvantages, disadvantages, epizootic disease, dissolved oxygen depletion, high technical know-how, water column, trophic niches, utilization of natural foods, grey mullet, tilapia, silver carp, synergism, balanced biological environment, artificial feeds.
Read the text and translate. Be ready to discuss.
Fish culture is classified based on the number of fish species as monoculture and polyculture.
1. Monoculture
This is the culture of single species of fish in a pond or tank used in running water system, recirculating system and in cages where the supply of natural food is limited. Under the conditions of pond culture with fertilization monoculture of single fish specie, the natural food available in the water column is not fully consumed by fish, therefore a combination of fish species differ in their feeding habits is preferred. The culture of trout, tilapia, catfish, carps are typical examples of monoculture. Monoculture of high value, market oriented fish species in intensive system is common practice.
|
|
|
Advantages of Monoculture:
1.Easy to feeding
2.Permits great control over size, age and sex
3.Easy to operate
4.Selective harvest of marketable fish can be employed
5. Suitable for farmers having limited land resources
Disadvantages:
1.Natural productivity of pond is not fully utilized
2.Available space in water column is not utilized
3.More chances of epizootic disease and parasites
4. More risk of water quality problem like dissolved oxygen depletion
Polyculture
·Polyculture is the practice of culturing more than one species of aquatic organism in the same pond. The most important consideration in polyculture is the probability of increasing fish production by better utilization of natural foods produced in a pond at different depths. Species successfully stocked together are differ in their feeding habits and occupy different trophic niches in the pond. Tilapia species, common carp, sliver carp and grey mullet are different in their feeding habits. Polyculture of common carp with all-male tilapia, and sometimes also with silver carp is a common practice in Egypt.
Success of polyculture depends on synergism and available food. Both tilapias and silver carp graze on algae, and thus help to maintain a balanced biological environment in which algal blooms are rare.
Advantages:
·Full utilization of feeding niche, space available in the water column, compatibility of species and artificial feeds
·Less chances to fail of the enterprises
·A variety of products available in the market
·Make more economic return than monoculture under same condition
·Plays an ecological role in maintaining water quality
· Less chances of epizootic diseases and parasites
Disadvantages:
·Difficult to harvest
·Difficult to maintain the food for all the species
·Need of high technical know-how
Exercise 39. Read and translate the following words and word combinations from Russian into English.
Система проточной воды, сом, истощение растворенного кислорода, кефаль, тилапия, эпизоотическое заболевание, преимущество, трофические ниши, искусственные корма, знание технических секретов, использование натуральных продуктов питания, сбалансированная биологическая среда, слаженная совместная работа, форель, собирать урожай, удобрение.
|
|
|
Exercise 39.Fill in the table according to the information in the text above.
| Monoculture | Polyculture | ||
| Advantages | Disadvantages | Advantages | Disadvantages |
Exercise 48. Make up collocations using words from both columns.
| epizootic | foods |
| trophic | know-how |
| feeding | carp |
| silver | diseases |
| natural | habits |
| grey | niches |
| technical | mullet |
Exercise 51. Test yourself by answering these questions and summarize given information.
Unit 10
Text A
Management of Culture System
Once the species for culture has been selected and the culture system has been constructed and stocked, aqua culturists must address various management concerns. In terms of things that should be monitored by the aqua culturists, 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 animals 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 respect 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 860F (300 С), while that for coldwater species is often 590F (150C). 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, aquatic animals are placed under stress. 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 establish the disease resistance status of the animals.
Dissolved Oxygen
Oxygen enters water by dissolution from the atmosphere and through the release 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 tilapia, 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 increase 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 animals respire continuously, the rate of oxygen production exceeds respiration and there is a net increase in the dissolved oxygen level. At dusk, when there is insufficient light for photosynthesis, the oxygen level begins to drop because of respiration demands, and the drop continues through the night. As long as the lowest morning dissolved oxygen level is not below about 5 ppm, there should be no problem. However, the lowest level of dissolved oxygen can change dramatically from one day to the next. Daily production of oxygen can be influenced by the weather (cloudy days don’t support as much photosynthetic activity as clear days) and by the biomass of culture organisms present. As the fish or shell-fish being raised grow, they extract more oxygen from the pond each day.
Ammonia
Ammonia occurs in two forms, unionized (NH3) and ionized (NH4). The ratio between the two depends on temperature, pH and a few other factors. Ammonia is rapidly converted to nitrate (N03) by plants and bacteria in aquatic systems. Thus, in ponds where there are plenty of plants and bacteria present ammonia toxicity is not usually a problem. In raceways and other water systems where animals are reared at high densities, ammonia removal is often not as efficient as in a pond, and toxicity can occur. Different species of aquaculture interest have different tolerances for ammonia. Tilapia can tolerate high concentrations of total ammonia (several ppm), whereas trout are highly susceptible to levels well below 1 ppm.
Text B
