IE73278B1

IE73278B1 - A method for producing molluscs

Info

Publication number: IE73278B1
Application number: IE930711A
Authority: IE
Inventors: David Llewelyn Hugh-Jones
Original assignee: Vokes Limited
Priority date: 1993-09-23
Filing date: 1993-09-23
Publication date: 1997-05-21
Also published as: GB9320464D0; GB2282039A; IE930711A1; GB2282039B; BE1005920A6

Abstract

Flat oysters are produced by introducing broodstock into a pond which is lined with a butyl rubber liner. Sidewalls 3, 4, 5, 6 of the pond are inclined downwardly to a base 2 which is inclined towards a drain sump 10 having an outlet 11. When the larvae have grown to 0.3mm mussel shells are dropped into the pond to provide a plurality of sites for the larvae to grow. After the oysters have reached a size of at least 3mm the mussel shells with the young oysters attached are scattered on the seabed.

Description

A Method for Producing Molluscs The invention relates to a method for producing molluscs and in particular flat oysters (Ostrea edulis).

According to the invention there is provided a method for producing flat oysters comprising the steps of introducing broodstock into a pond having a base and sidewall means which extend at an angle of from 130° to 170° to the base, the pond base and sidewall being lined with a liner having a friction gripping surface, growing the oyster larvae produced for a period of between 5 and 10 days to a size of at least 0.3 mm, dropping a plurality of discrete support bodies into the pond to provide a plurality of sites for the oyster larvae to settle and grow, maintaining the conditions in the pond at a pH of from 8.0 to 9.0 and a temperature of greater than 18°C, growing the oyster spat on the support bodies, emptying the water from the pond when the oysters have grown on the support bodies to a size of at least 3 mm in diameter, collecting the support bodies with young oysters attached, scattering the support bodies on the sea bed, and harvesting the oysters from the seabed when they have matured to marketable size.

Preferably the method includes the step of pumping water into the pond as required, and removing overflow water from the pond.

In one embodiment of the invention the support bodies comprise the shells of mussels.

Preferably the liner is of a black material and is preferably of an impermeable material. Most preferably the liner is of butyl rubber.

In a preferred embodiment of the invention the sidewall means extend at an angle of approximately 150° to the base.

In one embodiment of the invention water is removed from the pond through an overflow pipe which is pivotally mounted from a raised upright position for removal of overflow water to a lowered position for drawing the water from the pond.

In a preferred embodiment of the invention the base is inclined towards a pond drain outlet.

Preferably the pond has a depth of at least 1.25 metres.

The volume of the pond is preferably at least 500,000 litres .

In a preferred arrangement there are a plurality of ponds, each of the ponds preferably having a drain outlet with preferably the outlets of the ponds being interlinked.

Typically the method of the invention includes the steps of : depurating the harvested oysters in sterilised sea water;and grading and packaging the oysters.

In a particular application of the invention the method is used to breed oysters that are resistant to disease. Such an application includes the steps of : selecting a broodstock comprising parent oysters which have survived exposure to a disease; producing oyster spat from the selected broodstock; exposing these oyster spat grown from the broodstock to the disease; selecting first generation survivors of exposure to the disease; and repeating the breeding, exposing, and selecting steps .

In this case preferably the flat oysters are exposed to the disease by placing them in the open sea for a period following their production.

In one application the disease is Bonamia ostreae and the parent oysters are oysters which have survived exposure to the disease for at least three years.

In another application the disease is Marteilia refrigens and the parent oysters are oysters which have survived exposure to the disease for at least six months.

The invention also provides flat oysters, most especially flat oysters that are resistant to diseases such as Bonamia ostreae and Marteilia refrigens whenever produced by the method of the invention.

The invention will be more clearly understood from the following description thereof in which:Fig. 1 is a perspective view of a pond used in the method of the invention; and Fig. 2 is a side view of a pond overflow water removal system used in the method of the invention.

The method for producing flat oysters (Ostrea edulis) according to the invention comprises introducing broodstock into a pond (Fig. 1) which has a depth of at least 1.25 metres, preferably at least 1.4 metres and a volume of at least 500,000 litres. The pond is of generally rectilinear shape having a base 2 and sidewall means which in this case comprise four sidewalls 3,4,5,6 extending from the base 2. Each of the sidewalls 3,4,5,6 is in this case inclined at an angle of approximately 150 degrees to the base 2. The base 2 is also inclined downwardly, typically at a slope of approximately 1:50 towards a drain sump 10 having a drain outlet 11 to a drainage circuit 12. The base 2 and sidewalls 3,4,5,6 are lined with a liner (not shown) of heat absorbing black, preferably impermeable material which in this case is of butyl rubber. The liner provides a friction gripping surface having a friction coefficient which is sufficient to prevent the support bodies placed on the sidewalls 3,4,5,6 of the pond from slipping downwards.

Water is introduced into the pond through a water inlet 19. To control the level of water in the pond the outlet 11 is provided with an overflow pipe 20 (see Fig. 2) which is pivotally mounted at 21 for movement from an upright position with the pond at a desired full level Ll as indicated by full lines in Fig. 2 through an intermediate position for a reduced level L2 of water in the pond to the lowermost completely drained level. The overflow pipe 20 is lowered by a rope 25 attached near its top end and threaded through an anchorage eye 22 at the base 2 of the pond and back to surface level. The overflow pipe 20 is preferably of a plastics material and has a minimum diameter of 20 centimetres. Preferably there are a plurality of similar ponds with an interlinked drainage circuit. This, in conjunction with the overflow arrangement allows water to be moved between ponds to optimise growing conditions in each of the plurality of ponds.

In the method of the invention oyster larvae produced in the ponds is grown until the larvae have reached a size of approximately 0.3mm. Typically this takes between 5 and 10 days. At this stage a plurality of discrete support bodies, which in this case are preferably mussel shells, are dropped into the pond to provide a plurality of sites for the oyster larvae to settle and grow. During the growth of the larvae on the support bodies the conditions in the pond are closely monitored and the pH is monitored at from 8.0 to 9.0 and the temperature is maintained at higher than 18°C. The impermeable black body liner assists not only in preventing nutrient flow into the pond, but also assists in maintaining a higher temperature of the water in the pond.

Water is delivered into the pond through the inlet 19 as required to maintain the desired growing conditions in the pond. Overflow water is removed as described above and may be discharged to drain or re-distributed to other ponds to optimise growing conditions in all the ponds.

When the oysters in the ponds have grown on the support bodies to a size of at least 3 mm in diameter, the support bodies with the young oysters attached are collected and scattered on the sea bed. After a period of typically 3 years when the oysters have matured to marketable size they are harvested. The mature oysters are then typically depurated in sterilised sea water, graded and packaged.

In a particular application of the invention the method is applied to growing flat oysters which are resistant to a disease. Such oysters are produced by first selecting a broodstock comprising parent oysters which have survived exposure to the disease. Oyster spat are then produced from the broodstock as described above. The oysters thus produced are then exposed to the disease and first generation survivors of the exposure to the disease are used in repeating the breeding, selecting and exposing steps as required.

In the case of the disease Bonamia ostreae the parent oysters are exposed to the disease for a period of at least three years.

In the case of the disease Marteilia refrigens the parent oysters are exposed to the disease for a period of at least six months.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail.

Claims

1. A method for producing flat oysters (Ostrea edulis) comprising the steps of introducing broodstock into a pond having a base and sidewall means which extend at an angle of from 130° to 170° to the base, the pond base and sidewall being lined with a liner having a friction gripping surface, growing the oyster larvae produced for a period of between 5 and 10 days to a size of approximately 0.3 mm, dropping a plurality of discrete support bodies into the pond to provide a plurality of sites for the oyster larvae to settle and grow, maintaining the conditions in the pond at a pH of from 8.0 to 9.0 and a temperature of greater than 18°C, growing the oyster spat on the support bodies, emptying the water from the pond when the oysters have grown on the support bodies to a size of at least 3 mm in diameter, collecting the support bodies with young oysters attached, scattering the support bodies on the sea bed, and harvesting the oysters from the seabed when they have matured to marketable size.

2. A method as claimed in claim 1 including the steps of pumping water into the pond as required; and removing overflow water from the pond.

3. A method as claimed in Claim 1 wherein the support bodies comprise the shells of mussels.

4. A method as claimed in any preceding claim wherein the liner is of a black material.

5. A method as claimed in any preceding claim wherein the liner is of an impermeable material.

6. A method as claimed in any preceding claim wherein the liner is of butyl rubber.

7. . A method as claimed in any preceding claim wherein the sidewall means extend at an angle of approximately 150° to the base.

8. A method as claimed in any preceding claim wherein water is removed from the pond through an overflow pipe which is pivotally mounted from a raised upright position for removal of overflow water to a lowered position for drawing the water from the pond.

9. A method as claimed in any preceding claim wherein the base is inclined towards a pond drain outlet.

10. A method as claimed in any preceding claim wherein the pond has a depth of at least 1.25 metres.

11. A method as claimed in any preceding claim wherein the volume of the pond is at least 500,000 litres.

12. . A method as claimed in any preceding claim wherein there are a plurality of ponds.

13. A method as claimed in claim 12 wherein each of the ponds has a drain outlet and the outlets of the ponds are interlinked.

14. A method as claimed in any preceding claim including the steps of : depurating the harvested oysters in sterilised sea water;and grading and packaging the oysters.

15. A method as claimed in any preceding claim including the steps of : selecting a broodstock comprising parent oysters which have survived exposure to a disease; producing oyster spat from the selected broodstock; exposing oysters grown from to the disease; the broodstock selecting first generation survivors of exposure to the disease; and repeating the breeding, exposing, and selecting steps.

16. A method as claimed in claim 15 wherein the flat oysters are exposed to the disease by placing them in the open sea for a period following their production.

17. A method as claimed in claim 15 or 16 wherein the disease is Bonamia ostreae and the parent oysters are oysters which have survived exposure to the disease for at least three years.

18. A method as claimed in claim 15 or 16 wherein the disease is Marteilia refriqens and the parent oysters are oysters which have survived exposure to the disease for at least six months.

19. A method substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings .

20. Flat oysters whenever produced by a method as claimed in any preceding claim.

21. Flat oysters that are resistant to the disease Bonamia ostreae whenever produced by a method as claimed in any of claims 15 to 17.

22. Flat oysters that are resistant to the disease Marteilia refriqens whenever produced by a method as claimed in any of claims 15, 16 or 18.