Previous - Next
79. INCUBATION OF FERTILIZED EGGS
(A) If the water is obtained from a water body (1) it first enters a sedimentation basin (2) from which water is pumped through a sand filter (3) into a raised storage tank.
(B) If the water is obtained from a well, (1) it is pumped (2) directly to the storage tank. In both cases the quality of the water is improved by (4) its aeration in the storage tank.
If necessary, part of the water may be also heated and stored separately in the water tower.
(1) From the outside water tower the water enters the hatchery by gravity and fills a series of overhead storage tanks where the water pressure will equalize. The water may be used for various purposes, (2) such as the incubation of the fertilized eggs in jars. A pressure head of 0.5- 1 m is then advisable between the overhead tank and the incubation jars.
The two are mixed to produce the best temperature, in this case 22°-24°C for common carp.
In this case, two series of overhead tanks (1, 2) are required in the hatchery. Water mixing occurs below these tanks, for example before the incubation jars (3).
A pressure head of 1-1.5 m is then advisable between the overhead tanks and the jars.
83. The incubation of the fertilized eggs takes place in Zug jars (A).
A continuous vertical flow of well-oxygenated water through these jars may be maintained, the water entering at the bottom and overflowing at the top. This flow may be regulated at will by a valve. Usually, a series of Zug jars are placed in successive rows on metal frames (B). A common gutter collects the overflowing water of each row and drains it at one end. The Zug jar pictured here has a 7-litre capacity. It is made of thick glass, except for the top plastic collar. The funnel shape of the bottom part of the Zug jar which creates the water movement best suited to the gentle incubation of the eggs is particularly important.
84. To start the egg incubation, 7-litre Zug jars should be half filled.
The water inflow should be stopped and 1.5-2 litres of swollen carp eggs should be put in each jar (1). These will settle at the bottom of the jars (2). Open the water supply so that 0.6-0.8 l/min overflows at the top of each jar (3). The eggs are now gently moved around in the funnel-shaped part of the jars (4). It is useful to remember that each 7-litre jar may incubate the equivalent of 250-300 g of dry eggs. Knowing the total quantity of dry eggs to be used at any one time, the minimum required number of such Zug jars can be calculated. Vice versa, it is also possible to calculate the maximum quantity of dry eggs which may be incubated simultaneously, on the basis of the number of jars available.
(1) For the first 10 hours the water flow
should be regulated so that 0.6-0.8 l/min overflows at the top of
each jar.
(2) When the eggs have reached the end of the morula stage and the
blastula stage has begun, the water flow should be
increased to 1-1.2 l/min.
(3) Finally, when the tail, the eyes and the pigmentation of the
embryos become visible, the water flow should be
increased to 1.5-2 l/min.
86. The duration of the incubation period is closely related to the water temperature.
On the basis of the average of the latter during the day (°C) incubation of common carp eggs requires a total of 60-70 degree-days. This can be estimated from a simple graph showing (2) the length of the incubation period in days, in relation to (1) the average water temperature in centigrades.
The best water temperature for incubation ranges from 22 to 24°C which guarantees the production of strong larvae within a reasonably short time.
87. It is important to protect the eggs from fungal infection during incubation.
Every 6-12 hours, the eggs should be treated with malachite green, at a concentration of about 6 mg/l. A stock solution is prepared containing 500 mg/l. malachite green.
(1) The water flow is stopped in the jars to be treated, and
10 ml of the stock solution are poured into each 7-litre jar.
(2) The chemical is thoroughly mixed in the jar, care being taken
not to damage the eggs. (3) After about 5 minutes, the water
supply is reopened and (4) the chemical gradually washes out.
Soon they will be covered with the fungus Saprolegnia which endangers the fertilized eggs. In such cases, when the eggs have reached the eyed embryonic stage at the end of the second day of incubation, (1) the water flow should be stopped and (2) the eggs allowed to settle at the bottom of the jar. (3) The ring of white eggs at the top of the others can now be clearly seen.
(4) The dead eggs are carefully siphoned out of each jar, and the water flow is reopened. This operation should be repeated about 10 hours later, if necessary, before the hatching of the eggs occurs.
Such close and constant supervision will help to avoid important losses in production.
