A reliable 24-hour oil-free aeration system is essential for all hatcheries, in order to maintain dissolved oxygen levels in excess of 5 mg/L. A standby blower should be available at all times, as well as an emergency generator where power supplies are unreliable. Small, portable and generally cheap systems are available in many countries. Radial blowers are the most satisfactory and should have sufficient capacity to supply all operating tanks (water preparation, broodstock, larval rearing and Artemia hatching) simultaneously, at a minimum level of 0.5 m3/h of air for each cubic metre of water. The aeration system is a vitally important facet of the hatchery and every effort should be made to protect it from accidental damage or disruption. Further suggestions for ensuring the reliability of aeration are contained in New (2002).
Air distribution within hatchery tanks is normally through the use of 2.5 cm circular porous airstones (~1/m2 of tank bottom) or 20 mm PVC pipes perforated with a 0.8 mm drill bit at intervals of0.3to0.5 m. Currently, micro-perforated flexible tubes are available, which are more efficient in distributing air, although they are also more expensive. Good air distribution within each tank is essential to maintain even distribution of larval food and of the larvae themselves. This keeps each larva in close and constant proximity to food particles, which most hatchery operators view as essential.
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