GB2175486A - Food for benthic feeding aquatic animals - Google Patents

Abstract

A prawn feed presented in a gel matrix which is insoluble in water, the feed comprises a fine mash having a particle size between 100 and 220 microns and contains about 30% to 60% protein, water, and about .75% to about 1.75% of a gelling agent such as sodium alginate, the percentages being by weight based upon the total weight of the feed.

Description

SPECIFICATION Foodforbenthicfeeding aquatic animals The present invention relates to feed stuffs for benthic and demersal aquatic animals including marine and freshwater crustacea and fish.

It has been common to growthese animals using formula feeds manufactured inawaysimilartothat employed forterrestrial livestock feeds. The pellets are manufactured from a mash compressed at high pressure and raised to high temperatures and this can damage certain nutrients. In addition compression leads to a form of case hardening, appropriate to animals swallowing the pellets whole but highly inefficient and unassimilable in the case of prawns. It is a further disadvantage of thins pelletised form of feed that, in water, certain amino acids, vitamins and mineralswhich arewatersolublearelostthrough leaching thereby wastefully decreasing the food value and cost effectiveness of the pellet.The problem is exacerbated by pellet disintegration in water causing furtherwasteful losses and seriously increasing the potential pollution effect on the water.

Such an increase in pollution can inhibit growth ofthe aquatic animal and a consequent eutrophication inhibits efficient stock control assessment and forecasts of growth rates and increases the risk of disease.

All these problems are especially applicable to prawns. These animals in cultivation are highly efficient at selecting from the miscellaneous components ofthe detritus overwhich they browse particu larly as manipulation and mastication oftheirfood takes place outsidethe buccal cavity being achieved by complex movements of delicate and sensitive mouth parts. These processes are facilitated by the thixotropiccharacterofthe presentfeed material.

Accordingly prawns can be described as extremely fastidious fickle yet sometimes vigourously wasteful feeders with the result that any feed material designed forthem must meet very specific requirements in acceptability to the animal and in relation to the costs of manufacture transport and distribution at the feeding sites.

Mash currently employed in the manufacture of feed for prawns often includes particles which are too largeforimmediateconsumption bytheanimals.

When a prawn dislodges particles of feed from the pellet the large particles are often rejected and swept away by currents. Accordingly there can be considerable wastage through loss of material or rejection of the larger particles in addition to the problem of increasing the surface area of the pellet thus increas- ingthe likelihood of leaching andfurtherdisintegration. This is especially true of valuable and sensitive juvenile animals.

It is the object ofthe present invention to overcome or substantially amelIorate these disadvantages.

There is disclosed herein an aquatic animal feed presented in a gel matrix which is insoluble in water; said feed comprising a fine mash having a particle size between about 100 and about 220 microns and containing about 30% to 60% protein; water; and about .75% to about 1.75% of a gelling agent; the percentages being by weight based uponthetotal weight of the feed.

There isfurtherdisclosed herein a method of manufacturingasubstantiallywaterinsolubleaqua- tic animal feed, said method including the steps of providing a fine mash having a particle size between about 100 and about 220 microns and containing about30%toabout60% protein; providing about .75% to about 1.75% of a gelling agent; and mixing the mash and gelling agent with water to provide a gel matrix which is insoluble in water.

Preferably the gel matrix ensures that the resulting mixture is a self supporting paste ordough; the gelling agent is preferably a hydrocolloid, such as sodium alginate.

The preferred form of the present invention is described by reference to the following example.

Firstly a fine dry mash, having a particle size milled to 100 to 220 microns is produced. This is mixed with a sodium alginate (known as Manugel).The resulting material is mixed with approximately 30% fresh water, with a source of calcium ions (calcium sulphate dihydrate) with a sequesterant (Tetrasodium pyrophosphate). This produces a dough with a consistencysimilartothatofa baker's dough in which the mixing process avoids any shearing effect.

The dough is extruded by means of manually operated or mechanical devices under moderate pressure to a desired configuration, similar in appearanceto noodles, and this can be dried orfrozen.

Thefollowing isatableofatypical mixtureto be used in the manufacture of a dough feed prawns.

Product Approximate Description % Prot. kglmt Wheat Pollard 20 20 Meat Meal 50 110 Fish Meal 65 250 Prawn Head Meal 85 50 Sunflower Meal 38 429 Animal Pancreas Extract 85 140 Salt 1.45 Antibacterial agent 0.125 Antioxidant 0.125 Antimould agent 0.15 Tetrasodium pyrophosphate 11.9 Gypsum 7.0 Sodium alginate 14.0 Vitamin premix) Mineral premix) If required Fats The vitamin premix, mineral premix and fats listed above may be required ifthe various products listed above do not provide the dietary requirements of prawns.

The setting time of the gel can be predetermined with minor chemical ajustments according to the availability of calcium ions which are present as calcium sulphate. Tetrasodium pyrophosphate is used as a setting control agent i.e. its presence determines the rate of release of calcium ions. A typical setting timeforthe material is 15 to 30 minutes.

The alginate could be in the proportions of about .75% to about 1.75%, by weight, but more preferably about 1.4%.

Crustacean or mollusc meal and animal pancreas extract meal can be used in partortotal replacement of the sou rces of protein otherthanfish meal.

Atypical prawnfeed has the following crude analysis: Crude Protein 49.85% Calcium 2.81% Ash 12.00% Fats 7.7% Phosphorous 1.90% Salt 0.70% Is should be appreciated thatthe present invention is applicable to other aquatic animals apart from prawns. For example an aquatic animal food could contain 30% to 60% protein iffor example it is to be used to feed fish. For prawns, the food should contain 40% to 55% protein but more preferably 45% to 50% protein. The percentages being byweightbased uponthetotal weightofthefood.

When the feed material is presented in saltwater, the pellet like material remains stablefor3 to 5 days afterwhich itwill generally breakdown. When used in fresh water the gel can automatically rise to the surface after about 4 days subjectto watertempera ture,fermentation and a reduction in specific gravity.

On the other hand it is possible to prolong the period of stability in fresh water byfurther adjustment of the calcium ions.

The formation ofthe gel is facilitated by the calcium ions present in seawater. When the material is manufactured forfreshwater animalsfurther adjust- ment ofthe calcium content can ensure efficient gelling nonetheless.

As the gel matrix is insoluble yet soft, it prevents the leaching of essential soluble nutrients including vitamins by enveloping them in a medium which is softenoughtobeteased bytheprawnata pace consistent with its ingestion mechanism yet sufficiently rapid to preventfurther leaching.

The present invention in its preferred form has considerable advantage over previous pelletised feed inthatthe leaching of essential soluble nutrients (especially amino acids) is greatly reduced while the problem of pollution is considerably reduced and the particle size becomes far more acceptable to prawns and this minimiseswastage.

It should be appreciated thatthe mash employed can befurthertailored,tothe needs of particular animals to be fed by species and age, also facilitating the opportunist use of local raw materials.

Claims (15)

CLAIMS 1. An aquatic animal feed presented in a gel matrix which is insoluble in water; said feed comprising a fine mash having a particle size between about 100 and about 220 microns and containing about30% to 60% protein; water; and about .75% to about

1.75% of a gelling agent; the percentages being by weight based upon the total weight of the feed.

2. The animal feed of claim 1 wherein the gelling agent is a hydrocolloid.

3. The animal feed of claim 2 wherein the gelling agent is sodium alginate.

4. The animal feed of claim 1 wherein said feed has the consistency of a self supporting paste or dough.

5. The animal feed of claim 4wherein the feed has the consistency of baker's dough.

6. The aquatic animal feed ofclaim 1 wherein the mash contains 45% to 55% protein.

7. The aquatic animal feed of claim 6 wherein said mash contains 45% to 50% protein.

8. The aquatic animal feed of claim 4 wherein the gelling agent is in the proportion of approximately 1.4%.

9. A method of manufacturing a substantially water insoluble aquatic animal feed, said method including the steps of providing a fine mash having a particle size between about 100 and about 220 microns and containing about 30% to about 60% protein; providing about .75% to about 1.75% of a gelling agent; and mixing the mash and gelling agent with waterto provide a gel matrix which is insoluble in water.

10. The method of claim 9 wherein the feed is mixed so thatthe matrix ensures thatthe resulting mixture is a self supporting pasteordough; and the gelling agent is a hydrocolloid, such as sodium alginate.

11. The method of claim 10 wherein the mash, alginate and water are mixed so as to provide the feed with a consistency of baker's dough.

12. The method of claim 9 wherein the mash contains 45% to 50% protein and the gelling agentis in the proportion of approximately 1.4%.

13. The method of claim 9 wherein the gelling agent is sodium alginate.

14. A prawn food substantially as hereinbefore described with reference to the examples.

15. Amethod of manufacturing a prawn food substantially as hereinbefore described with refer encetotheexamples.