Ch07

Milt is added to the ripe eggs in dry conditions. The fertilization process occurs as soon as the fertilizing solution is added. The swelling and hardening of the eggs starts simultaneously.

70. To summarize, (1) the dry eggs are weighed and (2) the required amount of milt is added.(3) After thoroughly mixing the milt and the eggs, (4) fertilizing solution is poured into the bowl. (5) Fertilization takes place and the eggs begin to swell. (6) When the swelling is complete and the eggs have hardened they are treated with a tannin solution to remove their stickiness. (7) They are then ready for incubation in special jars.

71. The stripped eggs, henceforth termed "dry eggs", are weighed in their plastic bowl (2) which has previously been weighed empty (1).

The weight of the dry eggs may thus be easily calculated for each bowl. The necessary amount of milt may be determined on this basis (3).

72. Milt should be added to the dry eggs in the proportion of 1:100, i.e. 10 ml of milt are required per each kilogram of dry eggs.

For each batch of eggs it is advisable to obtain the milt from two different males, as a male is occasionally infertile.

In general, the milt collected from each male is sufficient to fertilize the eggs obtained from two females.

There are two methods of adding the milt to the dry eggs: (A) it may either be stripped directly into the bowl containing the eggs or, what happens more often, (B) the milt is poured onto the eggs from the collecting glass.

73. The fertilization of the eggs will be increased by the use of a fertilizing solution.

To prepare this solution (1) 40 g common salt Na Cl and (2) 30 g urea (= carbamide) CO(NH₂)₂ should be weighed. These two chemicals should then be added to (3) 101 water and (4) mixed well.

74. The dry eggs and the milt are gently but thoroughly mixed for a few seconds.

The fertilizing solution is then poured on the eggs in the ratio of 1:10, using 100 ml of solution per kilogram of dry eggs, while gently mixing with a plastic spoon. Fertilization is completed within 20-30 seconds but the mixing should continue for 3 to 5 minutes more.

75. As soon as the dry eggs come into contact with the fertilizing solution they begin to swell through hydration.

The swelling process lasts from 1 to 1.5 hours. Within this period (A) each litre of dry eggs will give (B) 6-9 litres of swollen eggs.

(1) The fertilizing solution should be changed three to four times during the swelling period to eliminate some of the stickiness of the fertilized eggs.

76. In order to remove every trace of the natural stickiness of the fertilized eggs, it is necessary to use a tannin solution. (1-3) This is prepared by adding 5 g tannin (= tannic acid) to 10 litres of water. (4) This solution is well mixed before being used.

77. The tannin treatment of the swollen eggs will not only dissolve the sticky layer surrounding the eggs, but it will also complete the hardening of the eggs.

(1 ) Approximately 2-4 litres of tannin solution are added to 2-3 litres of swollen eggs in a plastic bowl. (2) This is mixed rapidly, and (3) after a pause of 20 seconds (4) the bowl is filled with clean water.

Once the eggs have settled down, (5) the water is drained out. This rinsing is repeated twice, (6) then 1-2 litres of tannin solution are poured into the bowl. (7) This too is rapidly mixed, and there is another pause (8) this time for 10 seconds. (9) Clean water is again added, (10) followed by draining. (1112) This rinsing process is repeated twice. The fertilized eggs are now fully hardened and non-sticky. (13) They are ready for incubation.

78. In the hatchery rooms where stripping and artificial egg fertilization take place, various items of equipment should be available to ensure efficient working conditions.

(1) Large storage tanks with a good water supply are used for maturing the breeders. (2) Fish, water and chemical solutions are easily transported with a fibreglass tank on wheels. (3) Many plastic containers of various sizes are necessary. They include 3-4-litre bowls, 15-litre bowls (for egg swelling), 10-litre buckets, and 25-30-litre bins (for egg fertilization). (4) In a smaller separate room, smaller pieces of equipment (such as clean towels, measuring jugs/cylinders, plastic tubing, needles and thread, syringes, etc.) are stored, together with chemicals and the stock of dried hypophyses.

A production programme is followed, and its implementation accurately recorded every day by the hatchery manager.

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