| Operating systems in aquiculture
One can classify the operating systems in 4 types
the fisheries gathering
the mixed-farming of pond
controlled monoculture
monoculture in closed circuit
The fisheries-gathering
It is the simplest operating system and oldest. It consists in exploiting fish inventories without intervening on the external mailmen which condition the development of these inventories.
The awakening of the brittleness of a watery ecosystem and technological advances of these 20 last years deeply amended this mode of exploitation. The inventory control supplanted the blind exploitation of the fishing resources.
Indeed, the perenniality of the fisheries-gathering rests on the establishment of catching quotas and the introduction of a limiting size of fisheries in order to preserve a sufficient number sires to ensure a renewal of the species and to optimize the volume of the captures of the following fishing year.
Principle of management…
A given medium (a river, a pond, a portion of ocean) has a capacity of lodging in maximum biomass given. Thus, a medium not exploited and left with him even will reach a maximum capacity of lodging and will be stabilized. This stage, he will have there no more production of additional exploitable resources.
On the other hand, a reasoned exploitation of this medium will create “a vacuum” which will be filled with time while tending towards the maximum capacity of the medium. Management thus consists in being at a stage close to maximum capacity at the time of the period of exploitation of the inventories, by leaving enough individuals sires to allow the regeneration of the inventories in the time interval between 2 periods of exploitation.
Thus a medium where one carries out taking away produced in time more biomass than a medium where one does not take anything.
Encountered difficulties…
Resource management watery is a worldwide problem which must be based on an international regulation. These international scales explain the difficulty of implementation of this transfer.
The estimate of the inventories of sires is difficult to evaluate at sea. This estimate is generally calculated starting from the tonnage of the captures. However the systems of fisheries become more powerful increase the tonnage of the captures.
Balance-sheet…
The exploitation of a natural environment makes it possible to increase its output. A good management of the exploitation consists in constantly maintaining to sufficient inventories year sires by years.
The mixed-farming of pond
The mixed-farming of pond is a stage of exploitation of the aquicultural resources more elaborate than the simple fisheries-gathering.
The pisciculturist intervenes directly on the factors of production of a pond.
- It models its pond to facilitate the fisheries.
- It arranges at the bottom of the pond a channel to collect fish in period of fisheries.
- The depth of the pond does not exceed eters so that all the volume of the pond profits from the natural light favorable to the development of the phytoplankton.
It maintains its pond…
- It limits the higher plants to support the phytoplankton which is source of food of fish via the . It is clearing of weeds.
- It spreads quicklime at the bottom of the pond to increase the pH of water. A pH of 7 - 8 is favorable to the development of the phytoplankton. It is “liming”.
- It regularly cleans the ditches which are filled naturally. It is the clearing out.
It chooses the type of poisoning…
The quality and the quantity of fish are controlled.
It poisons with species with less less good commercial value.
- 30% of the basic fish biomass: carp (), tench (). They benefit from the lower part of the pond.
- 60% of the white fish biomass (fish of fodder): (), (), bleak (). They benefit from the upper part of the pond.
- 10% of the biomass in carnivores: boom ( Bored), pike () mainly and more recently the pike perch () and the (). They regularly take fish in the pond.
They are complementary from/to each other.
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Note: If there are too many pikes, the preys become insufficient. The production decreases. They die by cannibalism. If there are too many booms, the absence of sharp will force fish to nourish . They become dwarf.
- It limits the development of “undesirable” species. They are of commercial low value or are regarded as vermin with the development of the other species. Let us quote Bremen (), the (), the fish cat ( mixed), the boom sun () and the crayfish signal ().
- It controls the reproduction of the sires and the production of youthful. It produces eggs in a by maintaining with the shelter hard winter conditions of the sires. In a , it produces larvae.
Other species like the pin (), the (), the whitebait (), frogs and the crayfish (Crayfish crayfish, Crayfish ), are less common in pisciculture of pond.
Controlled monoculture
In this type of production, the pisciculturist completely controls the reproduction and the fuel supply. He does not control however two big factors: water and climate.
This controlled monoculture can take several forms. Let us quote the breeding out of floating cages and the breeding out of mining areas out-ground.
The floating cages are used for the breeding of salmon () or new species like the bar () and the sea-bream () in the Mediterranean. Cages are placed directly in the natural environment and one controls stocking with fish and food. The fish are completely dependant on exogenic food and are forwarded to the climatic risks. The breeding in monoculture makes it possible to optimize the fuel supply (specific food and food intake) and the reproduction (selection of stocks).
The mining areas except ground are used in places or one does not have sufficient space in the natural environment. This type of mining area is used for the production of (rainbow trout (), trout () and the salmon of fountain ()). Pisciculture except ground makes it possible to control the emissions pollutant resulting from an intensive breeding what is impossible in the case of the floating cages.
Controlled monoculture made it possible to support the business demand.
It is used for the majority of , the , the sturgeons and even some marine species.
Monoculture in closed circuit
The technological advancements of this last decade allowed the development of a new system of breeding which makes it possible to control the totality of the factors of production. It is what one calls the closed circuit, name which refers to the circuit of water inside the breeding: one always uses same water on the principle of recycling.
This closed circuit can be external or interior. It makes it possible to be freed from the requirements out of water, the climatic risks, the seasonal cycles and to control all the parameters. That makes it possible to increase the number of sites candidates to the creation of a pisciculture and also makes it possible to be interested in new “fragile” species or not adapted to the climate of the geographical area. That also opens the prospect to control the delicate stages of the breeding such as the sexual ageing of the sires and the larval breeding.
Principle of operation of the closed circuit
The basic principle of the techniques of filtration is of the same type that the systems and result from the principles and techniques resulting from industry from the water treatment. In fact technological advances of filtration made it possible to intensify the production by increasing the density of fish () and while making this mode of production profitable for the species with strong added value and the youthful ones.
Let us quote within this framework the breeding of and the boom or of turbot. Many other species is had a presentiment of with the gate.
The filtration of water is done in several stages. Mechanical filtration abolishes the suspended matter and one obtains muds. Comes then the most important stage which is the biological purification of water. Bacteria fixed on a solid support transform toxic nitrogenized waste into nontoxic soluble nitrogenized substances. Thus ammonia is transformed into nitrites and the nitrites out of nitrates. The pisciculturist must take care to fill the needs for fish like those of the bacteria. The main reaction is the following one:
During this aerobic reaction, it there acidification of the medium: the pisciculturist must rectify the pH by using carbonated solutions.
This system of closed circuit can be thorough to the extreme and recycling can be total: it is the concept of integrated circuit. There is no rejection in the external medium, therefore neither loss of energy, nor pollution.
Remarks received from Nicolas
Agricultural engineer - Doctorand in Ichtyology with
Laboratory of Animal Sciences of the of the University Henri de
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