07 September, 2010

Freshwater Fish Egg Incubators III.

2)  MacDonald Jars- 

      This type of incubator was developed in the US and is commonly used in the Philippines to hatch the eggs of Tilapia. The original incubator is about 5 liter capacity in size and made up of Plexiglas. A modification of this incubator is manufactured in the Philippines using fiberglass.    It has a 2 cm tube at the center where water with slight pressure passes.  There is a small clearance between the bottom of the center tube and the concave bottom of the jar to produce a jet of water that lifts the eggs slightly.  This is to prevent the eggs from stacking.  Since the eggs are dense and their tendency is to settle, the developed fry swims with the water flow and escapes through the spout of the incubator to another tank.
      With egg collection and incubation, the hatchery operators claim that high egg and fry production are achieved with this method as compared to the fry collection technique where they claim only 30% recovery.  Harvesting the eggs from the brooding female Tilapia also shortens its re-maturation period.

      The original MacDonald jar incubator can also be used to hatch eggs of other fish species like bighead carps, Pangasius, Red tail sharks, tinfoil barb, Pacu and other fish producing demersal type eggs.  Its only disadvantage is its small volume capacity. For big spawners producing big volumes of eggs,  several of these small sized incubator will be necessary. 

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