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Hatchery

135. Eggs and milt are mixed without water but washed clean a few minutes later. The fertilised eggs harden within 20 minutes or so and are then placed in a layer in trays or en masse in funnels. In the former case, dead eggs can be removed by hand although care must be taken to avoid damage to adjacent eggs. This it not feasible with funnels and we were informed that fungal infection is controlled by regular flushing with malachite green (see paragraph 217). Eggs must have a continuous flow of well-oxygenated water and must be shielded from bright light. They hatch in a few weeks depending on species and temperature and for a similar period lie more or less inactive whilst absorbing the contents of the yolk sac. When this is almost complete, the fry 'swim-up' and are fed fine particles of proprietary high protein food. This stage is critical and should be monitored carefully. Hygiene in the trays or troughs is important but farmers say that malachite green remains the main treatment for fungal contamination.

136. There is some evidence that fish fry need space for movement, exploration and interactions with each other but at a minimum the stocking density must allow adequate oxygen provision.