Hatching apparatus for pelagic eggs.

Background for the invention:

The invention consists of a hatching apparatus or incubator for pelagic eggs, to be more specific - a hatching apparatus of the type described in the introduction to claim

5 When pelagic fish eggs are hatched, part of the eggs wil die or be infected by bacteria/fungus which will form waste products. The eggs which have been destroyed will usually have a higher specific gravity than water and will consequently sink to the bottom. When hatching takes place i

10 traditional incubators it has been usual to remove dead eggs, remains of shell etc. by a suction tube along the bottom.

A second problem with such hatching units is that eggs and larvae are highly exposed to different kinds of infection This means that great care has to be taken with the water

15 quality. Ideally, only water which has been filtered and sterilized with UV light should be used.

Existing hatching units necessitate considerable work with the cleaning and the removal of dead eggs etc. If the dead eggs are not removed quickly and continuously, the water

20 quality will be impared. Though this can be compensated for b increasing the water flow, the bacterial culture is not removed, rather it becomes less concentrated. In addition, this is poor water economics.

A further disadvantage with existing hatching units is

25 spread hatching. The time of hatching is mainly determined by the physical environment surrounding the eggs, with the

temperature and supply of oxygen being the most important factors. Consequently, a hatching apparatus where the eggs lie in layers on the surface, as in existing hatching units, will result in a greater ^' hatching spread (unsynchronized hatching) than in a system where the eggs are distributed as widely as possible in the water mass. If hatching is spread, the larvae that have hatched early must be start fed before larvae that hatch late.

The purpose of the invention:

The main purpose of the invention is to design a hatching apparatus (incubator) for pelagic eggs, where it is possible to separate dead and heavily infected eggs from the others. This separation should be a continuous and automatic process. A further consideration is to create a hatching apparatus that provides the best water economics possible which has minimal filtration and sterilization costs. In addition, the hatching which is as synchronized as possible. These aims should be embodied in a simple apparatus which is economical to manufacture and maintain.

The principle of the invention:

The invention is based on the fact that there is a slight difference between the specific gravity of fresh eggs and those that are either dead or heavily infected. The incubator which is described has a structure that utilizes this difference to remove dead and infected eggs into a separate chamber which is automatically emptied.

The invention allows a hatching apparatus to be constructed which meets most of the requirements mentioned above, provided it is designed in accordance with the characterizing part of claim 1.

Other favourable features of the invention are mentioned in the subsidiary claims.

Example:

The invention is described in more detail below with

reference to the illustrations where:

Fig. 1 shows a schematic vertical cross-section through a hatching apparatus designed in accordance with the invention, whilst Fig. 2 shows an equivalent cross-section through an alternative means of designing a water level controller for a hatching apparatus designed in accordance with the invention.

The main element in the apparatus illustrated in Fig. 1 is a cylindrical water container 11, with a conical tapering base section 12, where the lower narrow end extends into a cylinder leading to the bottom chamber 13. the container is closed at the top by a lid 14, which has a protruding riser tube 15, attached centrally leading to the lower part of the conical base section 12. The riser tube 15, has a lateral opening 16, at the upper end, the purpose of which is explained below. An air tube 17, protrudes upwards from the centre of the bottom chamber 13, this is connected to the lower end of tube 15. The air tube 17, is connected to an air pump (not illustrated) for the supply of air under pressure. An alternative would be using a membrane pump, a compressor or such. The container 11, is filled with water upto the leve determined by the separate level controller 18. This will be described below. The container can be made of plastic, glass or metal. A transparent material would make it easier to monitor the eggs. The bottom chamber must be transparent. The container 11, is used to contain eggs of various marine species for incubation and hatching. When air is supplied under pressure through air tube 17, bubbles 19, will rise through the riser tube 15. The air expands as it rises to the surface capturing water which is forced out of the upper end of the tube through the lateral opening 16. This means that a current is created down into the annular chamber 20 in the container 11 around tube 15. This current flows downwards into the conical base section 12, towards the lower end of tube 15. The water flow through the conical base section 12,

will carry the dead eggs which would have otherwise been attached to the bottom. The current will help the separation of fresh and dead eggs since it is easier for the fresh ones to rise ut to the calm surface and form a layer 21 there, whilst the dead ones can be forced downwards more easily and led towards the lower end of the base section 12.

When the dead eggs reach a position under the riser tube 15, they will be in a back ebby and sink down in the bottom chamber 13. The dead eggs 22, are thereby collected here. The dead and heavily infected eggs 22, are removed by the water flowing along a tube 23, which leads horizontally out of the lower end of the bottom chamber 13. This can be done automatically by a valve opening for a few seconds. This can either be regular, 10-20 times a day, or it can be controlled by a photoelectric cell (not shown), mounted on the side of the bottom chamber.

The water consumption can be further reduced by designing the hatching apparatus for discoπtinuos (pulsating) water exchange. This can be done by the water level controller 18. The level controller 18, has a vertical main tube 24, which is closed by a bottom plug 25. From the bottom plug 25, the inside of the main tube 24 is connected to the container 11, through tube 23.

An overflow tube 26, is located sentrally in the main tube 24, tube 26 has an overflow orifice 27, at the water level required, this is extended down through the bottom plug 25. The bottom plug 25, also has a combined inlet and drainage tube 28, which forks from a junction 29 into a drainage valve 30 and inlet valve 31 respectively. When water is drained off, the supply of air through tube 17 is halted. With the correct salt content the fresh eggs in the water will rise up to the surface forming a layer 21. The water can then be drained off through valve 30 so as to remove the dead eggs 22. The amount of water which should be removed can be regulated by means of water level controllers, described below, either by time control or by extending the drainage tube 28 into tube 24, to equate the required level

for the remaining water.

After drainage, the system can be filled up with water again by opening valve 31. Though water filling can be controlled automatically by overflow tube 26, it is nevertheless advantageous for the sake of water economics to use a control system that closes inlet valve 31 after a certain time or amount of water.

The hatching apparatus in the example is equipped with a heating element 32, and a temperature sensor 33, which uses a non-illustrated control circut to supply energy to the heatin element 32, by in this case controlling the supply of electricity.

Fig. 2 shows an example of an alternative design for a water level controller 18*. Here only one tube is inserted in the bottom plug 25', i.e. tube 23', which is connected to the main container through the bottom chamber (fig. 1).

In tube 24* there is a bar 34, located centrally on upper and lower water level controllers, 35 and 36 respectively. A non-illustrated control circuit enables the two level controllers 35 and 36, to regulate two valves 30' and 31', for the respective supply and expulsion of water from tube 23'.

The hatching apparatus can automatically and continuousl remove dead and heavily infected eggs. It is also possible to replenish the water non-continuously. This results in a 70-90% reduction in the water requirements for egg treatment. Water circulation will furthermore result in more homogeneous conditions for eggs which will reduce the spread of hatching. This means that it is unnecessary to sort the fry prior to start feeding.

Alternatives:

As alternative configurations to the riser tube 15 supplying air, there are a number of other mechanisms which can create water circulation. It is conceivable that in some circumstances sufficient water circulation can be achieved by supplying air centrally. This may produce sufficient water flow down the walls to give the required sorting effect.

However, this would create a somewhat untidy current situation and stronger air bubbles will be needed to give adequate force. With some species of fish, in certain phases of the egg development the eggs should not be exposed to unnecessarily hard treatment and the riser tube will create a more laminar flow situation.

In some cases it will also be possible to use a pipe loop as the main container.

The water current can also be induced by fixing a screw impeller in the lower part of the riser tube. Gentle rotation would result in an adequate water current. This solution also has the advantage that the water circulation is concentrated in the lower end of the incubator which will give the eggs as gentle treatment as possible immediately after fertilization. This means that the fresh eggs which are on the surface will not be disturbed by the water circulation.

In this case, the riser tube can be equipped with two sets of overflow orifices, one set high up and the other in the lower part. If a housing is located around the tube, this can be moved to open the orifices as required.