106. Fertilisation takes place in a bowl or a bucket. The products of the male and female fish are kept in separate dry containers, the eggs with their attendant ovarian fluid. The sperm are checked for motility, by adding fresh water to a sample on a microscope slide, and then added to the bowl containing the eggs. Eggs should be disinfected following fertilisation but before water hardening.
107. After 250 degree-days, when they become 'eyed', the eggs are physically shocked. This is done by removing the eggs from the incubator and pouring them, without water, into a dry bucket allowing a fall of about 50cms. The infertile eggs then become white, and these can be removed by manual picking or automatic egg sorting machines. It is essential to inspect the eggs at frequent intervals for signs of fungal infestation. Good flows of clean, well-oxygenated water must be maintained throughout the cycle. Heated water can be used to speed up the development of the eggs. Heating is expensive and rather than letting the water flow to waste it is often recycled. This operation requires various systems to ensure the purity of the water; such as settlement tanks, ozone treatment and UV irradiation. At about 300 degree-days the eggs begin to hatch and hatching is completed within two or three days. Debris and unhatched eggs should then be removed.
108. For about a further 300 degree-days the alevin will survive and develop by utilising the yolk sac. Normal practice in the industry is to minimise energy utilisation, for example by using an artificial substratum (such as Astroturf) which gives the alevin something to lean against so that it does not need to swim upright. Alevins are negatively phototactic and are generally kept in the dark. If a light is switched on a burst of activity can be seen. Care must be taken if alevins are moved as the timing of first feeding is crucial and losses can be high if moves are mistimed.
109. As the alevins use up the last of their yolk sac and begin to feed they are termed 'fry'. The fry will grow to about 5g when they will develop the characteristic spots of the salmon and parallel ovoid markings on the flanks. This stage is called the 'parr'.
110. At several months old, parr are usually moved into outdoor tanks. The exact age varies in different production units and a few producers keep parr inside until they are actually transferred to sea cages as smolts, at which stage they are adapted to sea water. Water is continuously pumped through the tanks, ensuring a constant fresh supply and thus discouraging the build-up of any contaminated matter. Outdoor holding facilities should have some form of protection, for example netting, against predation (see paragraph 30).