Background of the Invention Fish farming is an increasingly thriving industry in many parts of the world.

Profitability, however, is badly affected by high feed costs which account for approximately half of overall operating costs.

Indeed, fish feed must, for nutritional reasons, contain about 35-50% protein. Protein, however, is expensive. This is due, in particular, to an excessive reliance on fish meal, the quality and prices of which are variable, with global supply declining despite increasing demand. The use of fish meal is also undesirable for environmental and water pollution reasons.

In addition to protein, fish feed should, ideally, also contain 40% or more oil.

Although oils are not, in themselves, expensive, methods suggested to date for incorporating oils into fish feeds have proved both costly and unsatisfactory.

If a significant quantity of oil is included in the feed components prior to their extrusion into pellets, the oil interferes with the extrusion process leading to pellets with relatively low strength and with a low oil retention capacity. Alternatively, if the oil is applied to pre-formed pellets, the oil is not properly absorbed and leaks out both during storage and in use resulting in reduced energy content, pollution and malfunctioning of feed-handling equipment.

In W098/49904, it was suggested that the above problems could be overcome by forming porous feed pellets by extrusion, drying, and absorbing oil into said pellets by vacuum coating. However, extrusion is an expensive process (both in terms of machinery and in terms of energy input required), it is not yet perfectly controlled and it gives variable results. In addition, extruded fish feed is very delicate and must be transported using specialised systems to minimise damage. What is more, the method suggested in W098/49904 does not, in practice, allow for the production of fish feed having an oil content of much over 35% by weight.

An alternative method (W097/22265) suggested coating the extrusion formed pellets with water soluble starches. Although this addresses the problem of poor water stability (many high oil content pellets of the prior art have a tendency to disintegrate when immersed in water), the resulting pellets could not support an oil content much beyond 25% by weight. In addition, the use of starches in the composition is uneconomical insofar as they are not (or only poorly) digested by fish. They therefore have no nutritional benefit and are considered to amount to wasted expenditure.

There is therefore a clear need for an alternative and more economical method of producing high oil content fish feed. The present invention provides such a method.

Summary of the Invention According to a first aspect of the present invention, there is provided a fish feed composition characterised in that it comprises 15-75%, preferably 20-75% by weight gluten (such as vital wheat gluten or corn gluten) and 25-85%, preferably 40-85% by weight dehulled oilseed (such as dehulled rapeseed).

In one embodiment, the composition may comprise: - 25-55% by weight, preferably 35-55% by weight lipids; - 30-75% by weight protein; - 0-15% by weight carbohydrate ; and - 0-5% by weight additives.

According to a further aspect of the present invention, there is provided a use of the composition as described in the preparation of a shaped, hardened, dried, flaked and/or coated fish feed, preferably in the preparation of fish feed pellets.

According to another aspect of the present invention, there is provided a fish feed pellet characterised in that it comprises at least 75% of the described composition and, in one embodiment, a coating.

According to yet another aspect of the present invention, there is provided a process for preparing a fish feed composition comprising blending 15-75%, preferably 20- 75% by weight gluten; 25-85% by weight, preferably 40-85% by weight dehulled oilseed; and optionally, one or more additional ingredients (such as additional protein or lipid sources, carbohydrate sources, and additives).

According to a further aspect of the present invention, there is provided a process for preparing fish feed pellets characterised in that it consists of (a) blending the ingredients of the fish feed composition; and (b) shaping the blend obtained in step (a) into pellets.

In one embodiment, said process may further comprise a step (cl) of treating the pellets obtained in step (b) with steam for 1 to 30 seconds and/or a step (c2) of coating the pellets obtained in step (b) or (cl).

Detailed Description The present invention relates to a fish feed composition comprising 15-75% by weight gluten and 25-85% by weight dehulled oilseed.

Gluten is the protein found in many grains and cereals such as wheat, corn, oats, rye and barley. The term"gluten"as used herein refers to gluten from any available source and to mixtures of gluten from different sources. The gluten may be in its native form, or it may be modified (e. g. hydrolysed). Preferably, the gluten will comprise 50%-100% by weight vital wheat gluten and/or corn gluten.

Gluten is comprised in the composition of the present invention in quantities of 15- 75%, preferably 20-75% by weight, even more preferably 20-50% by weight. In any event, the overall composition should ideally comprise 30-75% by weight protein (for some young fish, for example, it is desirable to have a protein content of approximately 70%). Preferably, the overall composition will comprise 35-60%, even more preferably 40-50%, by weight protein. If necessary, protein sources other than gluten can also be added. These can include any one or more vegetable or animal sources (such as soy concentrate, fishmeal or hydrolysed fishmeal), or mixtures thereof.

As mentioned above, the composition also comprises 25-85% by weight dehulled oilseed. Preferably, it comprises 40-85%, even more preferably 55-85% by weight dehulled oilseed.

Oilseed plants include rape, safflower, sunflower, soya, flax, cotton, mustard and crambe (or other plants of the Brassica genus) for example. Any one or more of these can be used as the source of dehulled oilseed. Preferably, however, rape, sunflower and/or flax will be used. More preferably, rape will be used. By removing the hull (which contains mostly indigestible carbohydrates), the amount of oil available from the seeds is substantially increased. Any method available in the art can be used to dehull the seeds. Preferably, however, the hulls will be gently cracked and removed without milling the seeds. According to one embodiment, the dehulling step will be followed by a heat-treatment step (e. g. heat shock). It has indeed been found that heat- treatment of dehulled rapeseed, for example, deactivates myrosinase and avoids toxic isothiocyanate formation during feed processing and storage.

If an additional source of lipids is required, this can be selected from any one or more vegetable or animal sources (such as soy oil, corn oil, palm oil, castor bean oil, maize germ oil, fishmeal or fish oil), or mixtures thereof. The overall content of lipids (i. e. lipids from dehulled oilseeds + optional additional sources of lipids) in the fish feed composition should preferably be 25-55% by weight, even more preferably 35-50 % by weight.

The composition of the invention may also contain one or more carbohydrates.

Preferably, it will comprise 0-15% by weight carbohydrate material. The carbohydrates can be used as binding or bulking agents or as a source of energy. In one embodiment, the carbohydrate will be selected from a cold water soluble starch, a starch derivative (e. g. starch ethers, starch esters, dextrins, etc. ) and mixtures thereof.

A cold water soluble starch is a starch which develops viscosity when dispersed in water at a temperature below 60°C, without the need for further heating.

Other additional feed ingredients may include vitamins and/or minerals, amino acids, pigments, antioxidants, colouring agents, enzymes, carotenoids, preservatives, pro- and/or pre-biotics, trace elements and any other compounds commonly used in small quantities in feed compositions. Preferably, the composition will contain up to 5% by weight of such additives.

The composition can be prepared simply by blending gluten and dehulled oilseed in the quantities specified above, if necessary with water and/or other aqueous solutions.

Where it is desired to include one or more carbohydrates and/or additives, these can be incorporated by blending with the other components of the composition. Blending can be carried out in any suitable mixer. These will be apparent to the person skilled in the art, but include, by way of example, ribbon mixers, plough shares, nauta mixers and continuous mixing screws.

The composition can be used in the preparation of high oil content shaped, hardened, dried, flaked and/or coated fish feed. In a preferred embodiment, there is provided the use of the above composition in the preparation of fish feed pellets.

Said pellets will advantageously comprise at least 75%, preferably up to 100% by weight of the composition of the invention. Ideally, the pellets will comprise 95-100% by weight of said composition.

It has surprisingly been found that despite the high oil content of the composition of the present invention, very little leakage occurs when the pellets are immersed in aqueous media. It is therefore not necessary to coat the pellets of the present invention to prevent oil leakages. Nonetheless, a coating can be applied if desired (e. g. to improve handling properties).

The coating will preferably include one or more cold water soluble starches or starch derivatives such as pre-gelatinised starch and/or maltodextrin. It may also (or alternatively) include one or more of wheat gluten, hydrolysed wheat protein and gelatine. Other materials suitable for use in coating fish feed pellets will be known to the skilled person.

It has surprisingly been found that the pellets of the present invention can be prepared simply by (a) blending the ingredients of the fish feed composition (as described above) and (b) shaping the obtained blend into pellets. According to one embodiment, the blend of step (a) can be milled (in a step (a') ) before being shaped in step (b).

Shaping can be achieved using any available means. Preferably, however, the pellets will be shaped using a die press, even more preferably they will be shaped using a conical die press. The dies may be of any suitable dimensions (e. g. 4x50mm ; 4x80mm ; 6x50mm) but will preferably have a diameter: thickness ratio of about 1: 20.

Preparation of the pellets as described above does not require heating or other potentially costly treatments. Thus, the use of an extruder for the preparation of pellets can be avoided. Accordingly, energy input can be reduced and, advantageously, the process can be applied at farm level (without the requirement for special machinery or skills).

The choice of the pellet shape, volume and weight will of course depend on the desired application. For example, different fish types will require different pellets.

The pellets of the present invention can be adapted for any type of farmed fish including yellowtail, sea bream, halibut, yellow jack, carp, trout, eel, cat fish and, most preferably, salmon. The specific (nutritional and physical) requirements for each of these fish types will be known to the skilled person.

According to one embodiment, the process of preparing the pellets of the present invention may comprise a further step (cl) of treating the pellets obtained in step (b) with steam for 1 to 30 seconds. This simple procedure allows the surface of the pellet to be hardened thereby further improving the pellets'oil retention and water stability properties. The thickness of the hardened layer will increase with the length of steam treatment and will affect the sinking behaviour of the resultant pellets. Thus, this steam treatment can be used to ensure that the pellets have the correct floatability for the type of fish being fed. It will also improve the pellets resistance against physical stress, for instance during storage, transport and distribution. When used, the steam treatment step will preferably heat the pellets to a temperature of 70-100°C, even more preferably to a temperature of 85-95°C.

Although not necessary, a coating step (c2) can also be included, as mentioned above.

Examples of materials that can be used for coating have been listed. The coating step can be used in addition to or instead of the steam treatment and it can include the application of several coats (depending, for instance, on the final thickness required), the application stages being separated by drying stages.

The invention will now be described in more detail by way of the following non- limiting examples.

Examples Fish feed compositions were prepared, using the following ingredients: - Vital Wheat Gluten (Cerestar : C*Gluvital 21000) - Corn gluten (Cerestar maize gluten meal Cl13871) - Low temperature (LT) Fish Meal 70% crude protein (Norsildmel) - Premix comprising 69% mineral mix, 27% vitamin mix and 4% Carophyll Pink CWS 10% formulation (DSM) - Sunflower Oil (Vandemoortele) - Dehulled rapeseed-extruded and/or heat treated if desired (Cargill) Mixture 1: g (as is) Oil (%) Oil (g) Protein (%) Protein (g) Vital wheat gluten 12 6 2.4 77 9.24 Corn gluten 9 5 0.45 60 5.4 Dehulled Rapeseed meal 60 50 30 35 21 Fishmeal 10 9 0.9 72 5.04 Sunflower Oil 8 100 8 0 0 Premix 1 0 0 50 0.5 Total 100 40.07 40.07 43.34 43.34 Mixture 2: g (as is) Oil (%) Oil (g) Protein (%) Protein (g) Vital wheat gluten 19 6 1.2 77 14.6 Dehulled Rape Seed meal 68 50 34 35 23.8 Sunflower Oil 12 100 12 0 0 Premix1005005 Total 100 47.2 47.2 38. 9 38.9 Mixtures 3 and 4: Mix 3 Mix 4 Dehulled rapeseed 36 29 Corn gluten meal 14.2 8.3 Lysine HC1 (Ajinomoto) 0.1 1. 1 Sunflower oil 2.9 7 LT fish meal 20 - Fish oil (Norsildmel) 10 10 Vital wheat gluten 15.8 41.8 Phosphate (Tessenderlo Chemie)-1. 8 Premix 1 1 Total Protein (%) 43. 3 46. 1 Total Lipids (%) 35 35 Mixtures 1-4 were blended and formed into pellets according to the following methods: Method 1 The components of the above compositions were put in a 11 cup and mixed in a blender (Waring Blender 8010, speed 22000 rpm with no-load), without additional heating, during 60 seconds. After mixing, a paste is formed in which all the oil of the composition is absorbed. This paste has sufficient firmness for it to be formed into a fixed shape. If necessary, firmness can be increased by the addition of 3-5% by weight water into the mixture during blending.

The blended fish feed was shaped by putting it through a meat mincer and cutting it at the exit. This resulted in a fish feed with a cylindrical shape, a diameter of up to 5mm and a length of approximately 10mm. Finally, the pellets were treated, for a few seconds, with steam to create a hard surface layer.

Method 2 A paste was prepared and shaped using a meat mincer as in Method 1. The shaped fish feed was then placed in a 250um sieve and a 10% suspension of pre-gelled starch (C*Gel-Instant 12005 from Cerestar) was poured over it. After sieving off excess suspension, the fish feed was powdered with pre-gelled starch. After gentle air drying, a hard surface layer was formed. If a thicker and/or harder surface layer is required, the treatment with pre-gelled starches can be repeated.

Method 3 A paste was prepared and shaped as in Method 1. Further treatment followed the same procedure as in Method 2 but with the following types of suspension and powdering: suspension powdering 10% pre-gelled starch Low DE Maltodextrin (Cerestar) 10% pre-gelled starch Vital wheat gluten (Cerestar: CAGluvital 21000) 10 % pre-gelled starch Hydrolyse wheat protein (C*Hypro W21100) 10 % pre-gelled starch none The different treatments described above all resulted in hard surface layers.

Repetitive treatments gave a thicker and harder surface layer. Differences in floatability were noticed depending on the type and the thickness of the surface layer applied.

Method 4 The dry ingredients of mixtures 1,2, 3 or 4 were placed in a dosing screw that forms the dry feeding supply of a Clextral BC45 extruder. Any fluid ingredients were blended and dosed to a pump that forms the wet feeding supply of the extruder.

The extruder was operated as a mixing device. No additional heating was used. The mixture left the extruder as a dough into which all the oil has been absorbed. This paste had sufficient firmness for it to be formed into a fixed shape. If necessary, firmness can be increased by the addition of 3-5% by weight water at the fluid inlet of the extruder.

Pellets were formed by cutting the paste at the extruder outlet using the rotating knife.

The extruder used to form the pellets had a circle-shaped exit resulting in cylindrical shaped pellets.

The pellets fell onto a perforated conveyer on which they were treated with steam for a few seconds, resulting in a hard surface layer.

Method 5 A paste was prepared and shaped as in Method 4. The formed fish feed fell on a perforated conveyer that ran through a bath containing a suspension as described in Methods 2 or 3. The fish feed was powdered and gently dried after excess suspension had been flowed off through the conveyer. The powder was the same as described in Methods 2 and 3. This treatment resulted in a hard surface layer.

In all of the above methods, pellets were formed with hard surface layers (either through steam treatment of by coating). The hard surface layer prevented oil from leaking and gave the pellets strength. As a result, the pellets were stable, did not loose oil and had a sinking profile adapted to e. g. farmed salmon production. Hardness was sufficient for resistance against physical stress during storage, transport and distribution.

Mixture 5 A fish feed based on the combination of wheat gluten, dehulled rapeseed and fish protein was prepared as follows: Formula g/kg Hydrolysed fish meal (LT 94) 50 Dehulled rapeseed 600 Vital wheat gluten 235 Whole wheat (Cerestar) 21 Fish Oil 50 L-Lys x HCL (Ajinomoto) 6 DL-met (Degussa) 3 Dicalphos (Tessenderlo Chemie) 20 Premix 15 Total 1000 Feed Analysis g/kg Protein 353 Lipid 379 Starch 50 Ash 65 Water 48 Phosphorus 10 Digestible Energy (MJ) 21 Digestible Protein/Digestible Energy (g/MJ) 14 Method 6 The above blend was pre-conditionned in a turbulator mixer with steam injection until a temperature of 75°C was reached. Pellets were then formed using a Heessen V3-30 press with hydraulic roll adjustment and a die of 5x75mm at a speed of +/-300kg/h.

The pellets left the press at 80°C. Thus formed, the pellets were cooled on a cooling belt under atmospheric conditions during 35-40 minutes before being packaged. The pellets were found to be of good overall quality.