Freshwater Fish Egg Incubators IV

3) Conical Jars or Funnel Type incubators

Funnel type incubators, as their name implies, are more or less funnel shaped.  Water flows in at the bottom through a short conical funnel and flows out over the upper edge of the incubator. The flowing water keeps the egg mass suspended and in continuous motion through the entire water column.

To prevent the eggs/newly hatched fry from escaping with the flowing water, an overflow with an 80-120 mesh stainless steel screen is fitted at the top of the incubator.  Water can be re-circulated while the embryo is still developing but has to be flowed through before the eggs are expected to hatch.

The incubators can be made up of fiberglass, G.I. Sheets or a combination of G.I. sheet to form the base cone while the body is made up of plastic drums and joined together by rivets.   Its capacities vary from 40–80 liters to as much as 200 liters.

In the funnel type incubators (including the MacDonald incubators), the eggs are kept moving and revolving continuously by the inflowing water that provides enough oxygen and removes the waste matter. The inflowing water is regulated to avoid damage to the eggs.

The funnel-type incubators are the most commonly used incubation devices in the country. It is used for both pelagic (i.e. bighead carp, rainbow and red tail shark, and tinfoil barb) and demersal eggs (i.e. Pangasius, African catfish, Koi and Common carp) whose stickiness has been removed.

Removal of egg stickiness

      This can be done only for fish that has been induced to spawn and stripped.  The stickiness of the eggs is activated once it comes in contact with plain water. Furthermore, the eggs will absorb water and expand and will not accept fertilization.  For this reason, it is important to towel dry the breeders well to avoid water from dripping to the eggs while stripping the male and female broodfish. During fertilization, it is also necessary to use 7% saline solution as an extender to the milt.  Salt not only prolongs the life of the fish sperm but also halts temporarily the development of egg stickiness.   After about a minute of fertilization, the eggs are washed three times with a 0.8-1.0 gram tannic acid dissolved in 1 liter of water solution.  This is then washed three times with the incubation water.