Rainbow Trout Farming Method
Planning the number and size of rearing devices of a new production unit
As fish grow, they need more and more rearing space. At the beginning, smaller tanks are enough, but later the fish stock has to be divided and restocked in reduced densities.
Therefore, it is advantageous to have both smaller and larger rearing tanks on a fish farm.
Planning in fish farming is usually done in a reverse direction. First, the final result (number, total and individual weights of produced fish) is set/fixed, and from these planned figures all the required rearing spaces of the different age groups of fish are calculated backward.
When planning for the number and size of rearing devices of a new rainbow trout production unit, the total quantity and the individual final size of fish should be taken into consideration, together with the fish density (intensity of production). The figures presented in Table 3 and 4 show the relative and absolute proportions of the required rearing spaces of the different age groups of rainbow trout.
The definition of a small-scale trout farm is rather subjective and may vary from country to country. In countries and regions where incomes equivalent to a few thousand United States dollars are attractive, a production of 2.5–5 tonnes of trout is already a considerable enterprise to start with.
The required space for producing 2.5–5 tonnes of trout depends on the final size of fish and the intensity of production. Tables 1–4 show the basic figures that are needed to plan table fish production.
In order to help production planning. When elaborating, it was assumed that the production of trout would be semi-intensive. With increasing water supply, the intensity of fish production and the quantity of fish in the devices can easily be increased.
The fish produced on a rainbow trout farm can be doubled if the conditions are favourable and both autumn and spring fry are reared. This is because the same rearing devices can be used twice a year. In this case, not only can the fry production be doubled, but also the fingerling and table fish production if the water temperature is high enough and the feeding is adequate.
Water supply and drainage
Water supply by gravity to a fish farm and its rearing devices and structures is important. This saves energy and, consequently, large amounts in terms of production costs.
The water supply to rearing devices can be done in two different ways. The rearing devices can be supplied either in parallel (separately) or in series. If the rearing tanks are connected to the water supply in series, the freshwater should be used first in tanks/ponds of younger fish, from where water flows into the tanks or ponds of older age groups of fish. Although arranging tanks in series is rather frequent, construction of new tanks should prioritize parallel water supply.
Especially in the case of a surface water* source, the construction of a water reservoir at the highest point of the fish farm will facilitate easy and efficient water management. The elevated central water reservoir will serve as a buffer, where water also settles. The water from the reservoir can be channelled to the rearing devices and structures through open canals, pipes or through a combination of these.
The rearing water should contain as much DO as its temperature allows. Aeration* ensures saturation of arriving water with air/oxygen. Aeration with a machine or the injection of pure oxygen* are very efficient techniques, but they are expensive. However, there are simple solutions/devices that can increase the DO of the arriving water.
Drainage of rearing devices and structures should also preferably be done by gravity in the simplest way possible.
At the point where water leaves rearing tanks and ponds, screens should be used. The mesh size of these screens should be dense enough to prevent fish not only from escaping but also from sticking into the screen or between the bars.
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