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منوي اصلي |
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لينکهاي سريع |
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موضوعات |
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آرشيو ماهيانه |
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لينک دوستان |
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جستجوگر |
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آمار بازدید |
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»تعداد بازديدها:
»کاربر: Admin
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تبليغات |
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AN INTRODUCTION TO WATER REUSE SYSTEMS |
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AN INTRODUCTION TO WATER REUSE
SYSTEMS
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The culture of freshwater and marine species has
received considerable attention in the public and private sectors as a new
agri-business to further diversify the agricultural and fisheries economies
of developed and developing nations. Much of the commercial production of
warmwatcr and coldwater species occurs in earthen ponds, tanks or floating
net pens or cages.
With traditional systems designs, fish production
requires large amounts of clean freshwater, precluding the production of fish
in many areas. The amount of water required for pond production depends upon
the pond seepage rate, rainfall, evaporation and culture intensity. In the
catfish industry in the US, the water requirements vary from 2.5% to 600Cl, of the total pond volume on an annual basis. For
"super-intensive" shrimp production as practiced in Hawaii, the
water exchange rate could be high as 80% of the pond volume per day (Wyban
and Sweeney, 1991). Comparatively, the production of fish in tanks and
raceways utilizes even larger quantities of water to remove waste products
from the production environment, typically 100 or more system volume
exchanges per day. An example is given by Ray (1981) for the intensive
production of catfish in raceways. The author estimated that the maximum
carrying capacity of the system was 160,000 - 240,000 kg of fish for every
available cubic meter per second (In3 S-1) of
water flow. The yearly production capacity of the system was 3 to 4 times the
carrying capacity. These figures can be used to estimate a water use of in
excess of 32,000 L/ kg of annual production (960,000 kg / m3 s-1 }. Phillips et al, (1991) compiled the water requirements for various
aquaculture production systems (Table 1.1). Table l.1 lists the water used
per kg of production for various freshwater and marine species.
The authors (Phillips et al, 1991) concluded that
"it seems inevitable that aquaculture will have to face increasingly tight
restrictions over development in many areas of the world, as
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T.M.
Losordo and M.B. Timmons
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Water Use Per kg of Production
of Aguacultured Products (After Phillips et al. 1991)
Species
and System Country Production Intensity Water Required
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Qsgl ha I r 2 ow •
17,400
30 - 50
3,000
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{~l kg.l 21,000 3,000 - 5,000 6,470
14,500 - 29,000 210,()(){)
252,000 11,000 - 21,340
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Oreochromis niloticus (Nile Tilapia) ponds Oreochromis niloticus (Nile Tilapia) ponds [ctalurus punctatus (Channel Catfish)
ponds I ctalurus punctatus (Channel Catfish)
raceways Salmo gairdneri (Rainbow Trout)
raceways Salmonids pond and tank
Pcnaeid Shrim[!, pond
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concern over environmental impact and competition
for resources grows". Indeed, concern over the impact of aquacultural
wastes and effluents has already brought aquaculture under the scrutiny of
many regulatory agencies in a number of developed countries. Aquaculture, as
other traditional agricultural operations, creates wastes that when
discharged to receiving waters, can have a detrimental impact to the local
aquatic environment (NRC 1992). In general, aquacultural effluents from
traditional production systems are characterized as high volume and
relatively low
•
strength wastes (Phillips et aI. 1991). Most
treatment technologies have been developed to
\
process more concentrated, domestic or industrial
wastewaters. In essence, the
treatment
processes for aquacultural wastewaters may parallel
those of tertiary treatment processes for domestic or industrial wastes. In
many cases, tertiary treatment of domestic waste waters is not applied due to
the high cost of implementing the processes.
These concerns for water supply conservation and the
environmental impacts of waste from aquacultural activities have focused
attention on the development of technologies for water reuse. Tn their simplest form, serial water reuse
systems increases the productive capacity of water (kg fish I L). Unless waste removal processes are
implemented after the last water use, water reuse does nothing in addressing
the environmental impact of aquaculture activities. Typically, reuse systems
for the production of salmonids, utilize some form of settling basin at the
end of each water use. In most cases, a significant fraction of the biochemical
oxygen demand (BOD) and organic nitrogen waste produced can be removed with
simple settling technology.
Like other aquaculture production systems,
recirculating systems generate wastes and are not an end in themselves to
reducing environmental impact. The wastes generated in recirculating systems
are in two forms: particulate and dissolved. The majority of the BOD and
inorganic and organic nutrients in the waste stream are carried in the
particulate form, usually measured as total suspended solids (TSS) (Chen et
aI. 1991). For this reason, the T'SS produced
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r.lrr. Losordo and M.B. Timmons
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Stocking
Density: Mass of cultured
product per volume of tank (ignores the effects of fish displacing part of
the water volume).
Flow
Through Rate: The volume of new water per unit time
passing through a cuI ture tank.
Menn Ilydrnulic Residence Time: Refers to the time required at a given
rate of flow for a complete volume of water in a tank to be exchanged, e.g.
Q(flow rate) I V (volume of tank).
Specific
Surface Area: Surface area
per unit volume; usually referring to the surface area of a particular media
used in filtration or settling components,
Carrying Capacity: The
maxitnum mass of aquacultured product that can be maintained within a culture
system; usually expressed as mass per unit volume of the culture system.
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The demand for high quality aquacultured products
and an increasing concern for resource conservation has led individuals and
large corporations to invest time and money in commercial scale recirculating
production systems. However, there are relatively few reports of profitable
recirculating production systems in operation. There is little doubt that
most fish reared in ponds, floating net pens, or raceways can be produced in
commercial scale recirculating systems, In calculating the cost of producing
fish in aquaculture, the investor must account for both fixed and variable
costs. Fixed costs or expenses are generally incurred in approximately the
same amount regardless of the volume of the production and sales of the
operation, i.e. salaries, depreciation, payments on loans (Spiller and
Gosman, 1984). A large portion of the fixed cost in a technologically
intensive operation is in servicing the debt incurred in getting into the
business and accounting for depreciation and maintenance costs. Servicing the
debt, whether in the form (If borrowed capital
or equity (your own funds) must be reflected in the cost of fish production.
Recirculating systems have generally been expensive to build, which increases
the cost of producing fish in these systems. Recent commercial scale
recirculating production systems investment costs have generally exceeded US
$4.00 - $8.00 invested per kg of annual production capacity, e.g. a system
with the capacity to produce 100,000 kg of fish per year cost $400,000 -
$800,000. In comparison, investment costs for commercial pond culture or
raceway systems seldom exceed $2.20 - $3.30 per kg of annual production
capacity.
The higher cost of producing fish in recirculating
systems have caused these producers problems in the market place when in
competition with producers using traditional pond
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T.M. Losordo
and M.B. Timmons
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• Determine if active
control of carbon dioxide levels in the culture water will be needed (Chapter
7);
• Provide for the control of pI-I and alkalinity
control in the culture system (Chapter 8);
· Provide for the
removal of fine solids not normally removed through mechanical screening or
settling by employing foam fractionation devices (Chapter 9);
· Develop an overall
management guide for the day to day operation of the system (Chapter 10);
• Define and select an appropriate alarm system
(Chapter 11).
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Considerable
background information on the basic processes being presented are also given
in each chapter to supplement the basic design information being provided.
These chapters should provide the reader essentially all the required
information in order to design and manage a water reuse system. Some of the
chapters provide information that apply beyond water reuse systems, such as
discharge control and effluent management from flow through systems and gas
concentration control in any type of water system.
The
book is written for engineers and biologists working in the area of intensive
fish culture. The text should also prove useful as an academic textbook, a
design manual for practicing aquaculturists and as a resource of current
"state of the art" tnethodologies associated with water reuse
systems.
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Chen, S., D. E. Coffin
and R. F. Malone. 1991. Sludge management for recirculating aquacultural
systems. Paper presented at the Workshop on Design of High Density Recirculating
Aquacultural Systems, Louisiana State University, Baton Rouge, Louisiana,
September 25-27, 1991.
Losordo, T.M., R.F. Malone
and S. Chen. 1992. Water quality requirements and environmental impacts of
recirculating aquaculture systems, Pages 1-19, In: Kissil, G.W. and L.Sa'ar.
Proceedings of the USA-Israel Workshop on Mariculture and the Environment,
June 8 - 10, 1992. Eliat, Israel.
Mayo, R.D. 1991. Review of 'water reuse systems -
water reuse in hatcheries. Pages 180197. In: Brune, D.E. and l.R. Tomasso.
Aquaculture and water quality. World Aquaculture Society, Advances in
Aquaculture Volume 3. Baton Rouge, Louisiana, USA.
National Research Council. 1992.
Marine Aquaculture: opportunities for growth. Report of the Committee on Assessment of Technology
and Opportunity for Marine Aquaculture in the
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Part three
Control and increase of production in
Fish cultivation
Introduction: The Concept of Production in fish cultivation
1 different concepts of production
in fish cultivation the principal
goal of fish cultivation in ponds is the production of fish of commercial value
for eating or restocking generally in as large quantities as possible and in
the shortest possible time.
However concepts differ sometimes
very much so according to the objective. Principally there are
Three: quantity, quality and
economic production.
Quantity production aims at
producing as great a quantity of fish as possible for eating or restocking.
The principal aim in not to produce
fish of high quality such as the production of graded fish.
Quantitative production means
production which will give the most weight, this in followed notably in Africa
with tilapias raised by the system of mixed age groups.
Quality production seeks to produce as high a quantity as possible of graded fish
either for eating or restocking.
Production in terms of weight is
never at maximum level although the fish of any given species produced are
generally of uniform size and weight and of great commercial value.
This kind of farming corresponds in
Africa to the rearing of tilapias by separate age groups.
According to bard (1962) this method
can give a production equal to two-thirds in weight of quantitative production
obtained by mixing age groups.
Economic production aims to produce
as great a quantity of fish of high commercial value as possible.
The fish of high commercial value as
possible.
The fish produced are either of high
consumption value such as gourami in the far East, or fish for restocking, not
to be eaten but with a high market value.
The production unit is not
necessarily found in the weight but in individual fish.
This is the case when fingerling
pike or pike-perch of 1 summer are produced in carp growing ponds.
Generally, in this case, the
quantity produced in weight is not very high.
Methods of raising can be extensive,
semi-intensive or intensive, depending on whether rearing is based on natural
food only or whether it is more of less entirely artificial. Extensive farming
Produces a quantity of fish without artificial
feeding, from rearing ponds which corresponds to natural productivity.
Intensive farming seeks to produce a
maximum quantity of subjects or weight in a minimum of water by means of
intensive or exclusive feeding.
Semi-intensive farming is intermediary.
2 means of increasing production
Whether production is quantitative,
quantitative or economic, there are many systems of controlling and increasing
output.
These are either biological or
non-biological.
A non-biological methods for increasing
production these are numerous and include:
I general technical and sanitary
methods.
Quite apart from the methods given
below and before applying them, general sanitary and technical are
indispensable if the farm is to be run
The following points, therefore,
must be observed; (1) different age groups must be represented normally and
judiciously; (2) a sufficient oxygen content must be ensured; (3) action must
be taken against disease and epizootics.
It is important to remember that all
production factors ply their part and that each one must be given even more
attention as in these ciroum-stances they are far from their optimum.
2 maintenance and improvement of
ponds.
Quite apart from the upkeep of
dikes, banks and other installations the maintenance and improvement of ponds
include principally;
(a) action against excessive water plants. This is carried out principally by
mechanical means (cutting), or by chemical means, as well as by biological means
(grass eating fish) in certain cases.
These are discussed in chapter XII.
(b) The improvement and restoration
of the bottoms of ponds.
The principal means used to this end
are to empty the principal means used to this end are to empty the ponds and
then when dry: to (1) leave the soil uncultivated or combine
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Fish Cultivation in floating cages |
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Fish Cultivation in floating cages
The Cultivation of freshwater fish in bamboo or wooden cages has been practiced for many years in the far East (Figs. 224 and 225).
In recent years, the technology for the intensive rearing of fish in cages has been introduced and improved in several countries throughout the world, for coastal marine waters as well as for inland waters.
The aim is to produce large quantities of fish on limited surface areas, in facilities less expensive and more manageable than ponds or tanks.
The use of rearing cages makes the fish harvesting very easy.
Another great advantage is the possibility of using water bodies in which classical fish culture cannot be carried out: large, natural or artificial non-drainable water bodies, slowly-moving water bodies with enough depth, thermal effluents.
The feeding of fish is entirely artificial and cages should be well sited in order to avoid unfavorable sanitary conditions.
In theory, intensive rearing in cages is possible for all species which accept complete artificial feeding such as trcuts, carps, tilapias and American catfishes.
Many details about cage construction and cage culture in freshwaters have been given by Dahm (1975) and Coche (1978).
Fixed cages made from nets or screen can be used, similar to those sometimes used for fish storage (Figs. 479 and 480), but cages floating at the water’s surface are most commonly used.
The principle of these floating cages is identical to the one applied for floating holding nets (Fig. 481).
Polyamide nets are often used, sometimes metal nets are also used, or a rigid construction made of metal or plastic screen.
The mesh size must be large enough to allow good water renewal.
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This may vary from 6 to 25 mm according to the species and size of the fish. For trout, the mesh size should not be smaller than one tenth of the length of the fish.
Floating is made possible by various means, such as barrels, usually in plastic, polystyrene floats, or closed PVC pipes. Floats can also be combined with working platforms which surround either a single cage or a series of them.
Cage management is easier with such working platforms.
Fish feeds are distributed either by hand or with automatic feeders.
Cages are often rectangular and dimensions may vary considerably.
Dahm (1975) considers as rather typical dimensions for cage culture in European inland waters.
Too large cages are difficult to handle, while too small cages may cause food losses because of the wild swimming of the feeding fish.
The cage walls should be at least 50 Cm (20 in) above the water’s surface.
In order to prevent bird predation, the cages are covered with either a net or a screen.
To protect the nets against rodents, a second net can be used, stronger and with larger mesh, or a light screen, or even a metal net.
A cheaper and generally sufficient solution to this problem consists of protecting the upper part of the net down to a 50 cm (20 in) depth, with plastified wire netting.
Floating cages are set up either in rather large standing waters or in slowly-running waters.
Often thermal effluents of power stations are used, if the water is clean enough.
The water depth below the cage bottom should be at least two or three metres, in order to avoid a lack of dissolved oxygen in case of an algal bloom. This will also reduce the risk of disease propagation, much higher in waters too rich in organic matter originating from fish faeces and waste feed.
In fact, floating cages should not be set up in standing waters less than five metres (5 yd) deep.
To be successful, enough dissolved oxygen should be present in the cages.
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In standing waters, the water renewal is often due to wind-induced currents.
To take full advantage of such currents, it is advisable to set up the cages perpendicular to the main currents.
Net fouling organisms may also reduce water renewal.
Regular checks and maintenance are therefore necessary.
Anti-fouling preparations (copper salts,star) or special paints can be applied to slow down the development of fouling organisms.
If necessary, pumps or any other aerating systems can improve the water oxygen content (Chap.XII, Sect.III).
The size of the rearing facilities depends on many factors : fish species, water renewal, depth and surface of the water body, acceptable degree of eutrophication.
It can be considered that the wastes load produced by the intensive rearing of 100 kg (220 lb) of fish is equivalent to that of five inhabitants.
Mann (1974) reports that in an old 17-5 ba gravel-pit, 5-9 m (5-10 yd) deep, the distribution of about 100 tons of dry concentrated feeds for the anneal production.
Such production has been obtained in 40 cages with a total volume of nearly 2500 m3 which means an annual yield of 20 kg (42 lb) per m3 of cage.
Exceptionally high productions can be obtained in heated effluents of good quality and sufficient flow.
Coche (1978) reports average monthly productions of 35 kg (78 lb)/m3 for common carp, 20 kg (42 lb)/m3 for Ietalurus pumetatus, an American catfish, and 15 kg (33 lb)/m3 for rainbow trout.
For rainbow trout rearing in non-heated waters, an annual production of 25 kg (55 lb)/m3 is normal.
This production is attained with a stocking density of 10 kg (22lb)/m3 and a maximum final density of 35 kg (78 lb)/m3.
The conversion rate of dry pellets is about three.
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nutritional disease |
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The
earliest recognized nutritional disease syndrome of cultured penaeids was originally
named "black death" to describe the typical, large black
(melanized) lesions that occur in dying shrimp (Lightner et al. 1977; Magarelli
et al. 1979). The disease occurs in penaeids reared in closed systems,
aquaria, or flowthrough systems in which most or all diet is artificial and
without adequate ascorbic acid supplementation. The disease has not been
observed in shrimp cultured in ponds, tanks, or raceways where there was
primary productivity (growth of algae) (Lightner et al, 1979). Shrimp with black death typically display
blackened (melanized hemocytic) lesions in tissues with a high collagen
content. Such lesions are present in the stomach wall, hindgut wall, gills,
and subcuticular tissues at various locations in shrimp, especially at the
junction of body and appendage cuticular segments. There is often a terminal
bacterial septicemia in shrimp with clinical signs of black death disease;
Vibrio spp. and other opportunistic bacteria are typically isolated from the
hemolymph of affected shrimp. Black
death disease has not been observed in subadult and adult shrimp and is
apparently confined to the juvenile stages of the species. Penaeid shrimp
apparently have a limited ability to synthesize the vitamin that meets
the nutritional requirements of the older life stages, but not of the more
rapidly growing juveniles stages (Magarelli et al. 1979)
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زبان تخصصی قسمت ششم |
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The female brood fish are taken out and wipend gently with a
towel to remove all adhering water , after which the eggs are stripped and
collected in a dry bowl ( fing .2.2 ) . depending on the size of the fish and
consequently the quantity of eggs two or four females may be stripped at a time
. afterwards the male are stripped and the milt is poured over the eggs evenly
so as cover as many eggs as possible , the they are mixed well with a feather
or spoon and allowed to stand for a minute or tow . the water is poured in
slowly to fill the bowl and allowed to stand for about 10 min . at first one of
the eggs stick to the pan , but they swell with water , the volume is increased
and finally the stick to the pan only by a tiny point and can be detached
easily . because of the excessive amount of milt the water is clouds and
therefore is replaced several times until the eggs are seen to be very clean
and the water clear . the eggs are then poured slowly on to incubation trays
where they are uniformly spread out in one or several layers .
Lesson III
Artificial breeding of sturgeons
Different phases of
sturgeon cultivation are similar to those of other restocking cultivations
based on the capture of brood fish from open water , followed by artificial fertilization
and hatching . according to each group ,sturgeons reproduce either in the
spring at the end of that season or in the autumn , but in general between
april and august and sometimes up to October ( fig . 2 .3 ).
In order to hasten maturity and spawning , sturgeon pituitary
gland extract is injected at the rate of 2 – 2 .5 mg dry weight per kg body
weight in females and half of that in males . carp pituitary injection at the
rate of 4-5 mg per kg body weight is also reported to be effective . injected fish are held in tanks until they
are ripe . between 24 and 36 hours after injection the brood fish should be
mature .
Artificial fertilization in sturgeons differs slightly from
the method generally used for other fish . as the fish are too large and
difficult to handle and the structure of the oviduct allows only partial stripping
, they have to be killed for eggs collection . a ripe female is stunned and
suspended from a hook . the abdomen is slit open to remove the eggs , taking
care prevent loss of loose eggs through the genital opening when pressure is
exerted . the eggs are collected in a pan placed under the fish . they are
given a first washing which lasts a maximum of 5 minutes . the removes the
blood and the mucus . a little water is then poured in the eggs which are
sprinkled immediately by the milt from two or three males . mixing is done with
the hands and the eggs then allowed to rest for 3 4 minutes until fertilization
is terminated . this coincides with the hardening of the shell which will be
both resistant and elastic .
The a second washing is done to remove excessive sperm and
the sticky coating covering the eggs . in this way the eggs will neither stick
together nor to the bottom of the hatching apparatus . the water used for
hatching should contain 10 per cent finely powdered clay or chalk . running
water should be used or renewed several
times . gradually the viscosity will disappear and after 20 to 30 minutes the
second washing should be terminated salmon incubators can be used for hatching
on the temperature and the species . but is seldom more than six days at 15°c . the yolk
sac is absorbed in 5 – 10 days.
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مطالب پيشين |
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درباره |
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تکثیر و پرورش آبزیان
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نويسندگان |
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لينك دوني |
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پشتيبان |
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