DRY FISH FEED AND METHOD OF PREPARING SAME

Abstract: A fish feed composition for carnivorous fish, having a composition essentially corresponding to that of the natural prey of the fish is provided. The feed comprises a wetting agent and/or an emulsifying agent, 30-70 wt.% protein, 20-50 wt.% of lipid and 0-10 wt.% carbohydrate. In particular, the carbohydrate is at the most 2 wt.%. Methods for preparing the feed are also provided.

Description: DRY FISH FEED AND METHOD OF PREPARING SAME FIELD OF INVENTION The present invention relates to the provision of a novel, nutritionally optimized dry fish feed for use in farming of carnivorous fish, the composition of the feed essentially corresponding to that of the natural prey of carnivorous fish. TECHNICAL BACKGROUND AND PRIOR ART Fish can be divided into two major groups, carnivores and herbivores, according to the type of feed they consume. Carnivorous fish include predatory fish such as salmonoids (trout, salmon) and eel which are reared in large quantities in aquacultural operations in many countries. Major problems associated with aquaculture are (i) the requirement to optimize the feed composition with respect to a high growth rate of the fish and a high feed conversion rate and (ii) to prevent that the fish are attacked by infectious diseases and (iii) to minimize the level of contamination with organic matter of the rearing water environments (tanks, ponds or fenced sea areas) and recipients for such water. The natural fish prey for carnivorous fish such as salmonoids has with respect to the major components, the following typical composition on dry weight basis: 45-90 wt% of pro¬ tein, 20-50 wt% of lipids, 5-12 wt% of ashes and nitrogen free extracts (NFE) . From the above it can be seen that the variation in composi¬ tion of the natural prey for carnivorous fish is relatively large. This is i.a. caused by the fact that in smaller prey fish the volume of the stomach constitutes a relatively larger proportion of the total weight as compared to that in larger prey fish. Additionally, seasonal fluctuations will affect the composition of the fish prey which e.g. implies that the lipid content is at the highest level in the autumn and at the lowest level in the spring. Commercially available dry feed compositions for carnivorous fish have a content of nutrients which differs significantly from that of the natural prey fish. Thus, such feed composi¬ tions commonly have a relatively high content of carbohy¬ drates which are incorporated to act as a binding/structure forming agent in the pellets/granules of the feed. The carbo- hydrate sources are typically starch-containing cereals such as wheat or cereal starches. The conventional processes for preparing such types of fish feed normally include an extrusion pelleting process whereby the carbohydrate-containing feed mixture is pre-cooked at temperatures above the starch gelatinization temperature followed by an extrusion step wherein the feed mixture is cooked together with the other feed ingredients at a tempera¬ ture above 100°C, resulting in solid, dry feed pellets. In the known methods of manufacturing dry fish feed, carbohy- drates in amounts from about 8 to about 20 wt% is an ingre¬ dient which in the industry is considered as required to obtain a fish feed having a sufficient long term stability towards disintegration and deformation during storage and distribution. Additionally, currently available fish feed compositions have a relatively low content of protein and lipids. Thus, DE 3707032 Al discloses a water insoluble extruded fish feed for aquarium fish containing 30-50 wt% protein, 5-15 wt% lipid, up to 10 wt% carbohydrates and having a moisture content in the range of 5-15 wt%. NO 147858 discloses a fish feed compo¬ sition in the form of granules having a maximum dimension of 300-2000 μm and consisting of 30-80 wt% protein and up to 40 wt% carbohydrate, 0-20 wt% lipid and at the most 15 wt% vitamins and minerals. In CH 627 623 is disclosed a fish feed for fresh water and salt water fish which contains less than 5-10 wt% of lipid. As an exception to the above mentioned fish feed compositions which all contain a substantial proportion of carbohydrate, the fish feed disclosed in EP 0 292 052 A2 consists of 80-100 wt% protein raw material and 0-20 wt% of a bonding agent consisting of fish oil and lecithin. However, none of the above fish feed compositions have a nutritionally optimized composition i.e. a composition essen- tially corresponding to that of the natural feed of carnivo¬ rous fish. Rather, the composition of commercially available fish feed is selected so as to fulfil technological require¬ ments e.g. to provide structure-forming or binding agents to allow extrusion and granulation of the product mixture and the requirement for the finished feed product to have a form and structure that is stable towards deformation during storage and transportation. It is known that the composition of currently available feed compositions for carnivorous fish is associated with several nutritional problems. Thus, a high content of carbohydrates may result in a diabetes-like condition, enlarged fatty liver and a reduced metabolism of proteins. Recently, it has been attempted to raise the lipid content of fish feed in order to increase the energy content of the feed. As one example, WO 96/01058 discloses a feed composi¬ tion with a very low content of carbohydrate and containing about 27 wt% of fish oil which is added during the manufac¬ turing process by spraying it onto a mixture of pressed, wet fish material and stick water. The resulting mixture is formed into pellets by means of an extruder/pellet press process. In WO 92/16115 is disclosed a "weaning" fish feed without added carbohydrates and comprising micronised fish meal of a selected, high quality, 15-35 wt% marine fat, vitamins, minerals and gel-forming glue water which is mixed and formed into roe-like particles by an agglomerating step by means of cutting forces (e.g. using rotating plates or knives or a fluidising technique) and bonding agents. How¬ ever, when administering the resulting feed particles to fish fry breeding vessels, a disintegration of the particles occurs whereby 10-20% of the feed is leaked to the surrounding water after 30 minutes, which contributes to pollution of the water. The above processes of manufacturing fish feed having a relatively high content of lipid either requires an extrusion step involving that the feed mixture is subjected to heating above 100°C inevitably resulting in a reduction of the nutri¬ tional value of the protein component, or the use of compli¬ cated process steps such as micronising and agglomerating equipment . A well-known problem with fish feed is the disintegration or dissolution of the feed particles after administration to the breeding vessels or ponds which results in loss of feed and pollution of the water. This problem is particularly pronoun- ced when the carbohydrate content is low. Thus, it is apparent that dry fish feed for carnivorous fish having a composition essentially corresponding to that of the natural prey and which can be manufactured by a simple pro¬ cess to provide feed having a high nutritional value in the form of particles which have a sufficiently coherent struc¬ ture to prevent disintegration hereof in the water has not hitherto been available. The present invention provides such a simple process and feed compositions. Thus, the advantages obtained with the fish feed composition according to the present invention include: - optimized feed uptake resulting in an increased growth rate of the fish, improved health and enhancement of defence mechanisms towards disease attacks . - eliminating malnutrition and adverse conditions such as fatty liver and diabetes-like condition, - provision of a high energy feed for growing fish, resulting in a more cost-effective feed, since the coef- ficient of utilisation (i.e. the feed conversion rate) will be higher as compared to that of a feed with a high carbohydrate content and/or low lipid content, - a reduced amount of faecal matter/waste products in the rearing environment and recipient water as a result of a better feed conversion and essentially no disintegration in water of the feed particles, thereby also providing a highly desirable environmental benefit. SUMMARY OF THE INVENTION Accordingly, the invention relates in a first aspect to a nutritionally optimized dry fish feed composition for carni¬ vorous fish, the feed having a composition essentially cor¬ responding to that of the natural prey for said fish, the feed comprising 30-70 wt% of protein, 20-50 wt% of lipid, 0- 10 wt% of carbohydrates and a wetting agent and/or an emulsifying agent, the amounts of the components being based on the total weight of the feed. In a further aspect there is also provided a method of pre¬ paring such a fish feed composition, the method comprising the steps of (i) mixing a lipid and a wetting agent and/or an emulsi¬ fying agent, (ii) adding to said mixture the protein in the form of an aqueous suspension and/or solution, (iii) subjecting the resulting mixture to emulsifying conditions, and (iv) subsequently forming the resulting emulsion into particles, which are subjected to cooling and, if required, drying to obtain the feed composition. In a still further aspect, the invention relates to a method of preparing the above fish feed composition, the method comprising the steps of (i) preparing an emulsion comprising a lipid, an aqueous phase and a wetting agent and/or an emulsifying agent, (ii) combining the emulsion with at least one dry fish feed ingredient to obtain a fish feed mixture, and (iii) subsequently forming the resulting emulsion into particles, which are subjected to cooling and, if required, drying to obtain the feed composition. DETAILED DISCLOSURE OF THE INVENTION The present invention provides, as mentioned above, a dry fish feed composition for carnivorous fish, the feed having, with respect to the major dietary components, a composition essentially corresponding to that of the natural prey for such fish. The feed is dry, i.e. it has a moisture content which is preferably at the most 15 wt%, such as at the most 10 wt%. In one advantageous embodiment the feed composition has a total content of protein and lipid which is at the most 85 wt% such as at the most 80 wt%. One interesting aspect of the invention is the possibility of adjusting the ratio between protein and lipid, thereby providing compositions adapted to particular customer demands, e.g. compositions specifically adapted to particular species or life stages of fish. In useful embodiments the weight ratio between lipid and protein is in the range of 1:1 to 1:5 such as e.g. in the range of 1:2 to 1:3. An interesting embodiment of the invention is a fish feed composition with a high energy content resulting in a more cost-effective feed, as the coefficient of utilisation (feed conversion rate) is higher compared to that of a feed with a high carbohydrate content and/or low lipid content. Thus, in one preferred embodiment, the lipid content is in the range of 20-40 wt%. The lipid can be any vegetable lipid and/or marine lipid which may either be solid or liquid at room temperature. One presently preferred lipid is a fish oil, including an at least partially hydrogenated fish oil . How¬ ever, the lipid may also be selected from other sources such as oils and fats from other animal sources and vegetable oils and fats. In one preferred embodiment, the protein content of the feed is 40-65%, preferably 45-60 wt% and more preferably 50-60 wt- %. The protein source may be a liquid or dry non-milk protein source, such as stick water (also referred to as size) , fish meal, blood meal, meat meal, bone meal, liquid or dry yeast or proteins derived from a vegetable source including as examples soy beans, peas, maize or cereals. Evidently, a protein source of marine origin has an amino acid composition which is nutritionally appropriate for growing fish, i.e. such a protein contains essential amino acids in the appropriate amounts . This may not be the case with other protein sources, and it may therefore, when non- marine proteins are used in accordance with the invention, be required to supplement the feed composition with appropriate amounts of certain essential amino acids with respect to which the selected protein is deficient, including as examp- les tryptophan and methionine. A currently preferred protein source is a marine protein source such as fish meal or fish material having a water content in excess of 10 wt% including the semi-manufactured press cake material from fish meal production and stick water also from the processing of fish raw material for fish meal production. However, the quality of such protein materials may vary considerably. In certain fish feed compositions e.g. the so-called "weaning" feed compositions, it is preferred to select fish protein sources of a high quality e.g. having a low content of soluble nitrogen components, a low content of biogenic amines, a low content of carbohydrate, a low content of lipids or containing lipids having a low degree of rancid¬ ity. Furthermore, the digestibility of the protein should be high such as at least 90%. Therefore, in one aspect of the present invention the feed composition contains such a high quality marine protein source. Adverse conditions in fish such as fatty liver and diabetes¬ like conditions caused by a high content of carbohydrate in conventional fish feed compositions can be prevented by the feed composition according to the present invention. Accor¬ dingly, it is an important aspect of the present invention that the carbohydrate content is low. Thus, the content hereof is preferably at the most 8 wt%, more preferably at the most 7 wt%, most preferably at the most 6 wt%, including at the most 5 wt% such as at the most 4 wt%. It is particu¬ larly preferred that the carbohydrate content is at the most 3 wt%, including at the most 2 wt% or even at the most 1 wt%. In accordance with the invention the feed composition may comprise an emulsifying agent (emulsifier) , such as a fatty acid, a mono- di- or triglyceride, an organic ester of mono- glycerides, a polyglycerol ester of fatty acids, a propylene glycol ester, a sorbitan ester of fatty acids, a polyoxyethy¬ lene sorbitan ester, a sodium stearoyl lactylate, a calcium stearoyl lactylate, a sucrose ester of fatty acids, a sucro- glyceride, a lecithin or a mixture of such emulsifiers. Particularly preferred emulsifying agents are water-in- soluble. In specific embodiments the emulsifier is derived from a marine source. The amount of emulsifying agent is typically in the range of 0.1 to 5 wt%, calculated on the amount of lipid such as in the range of 0.5 to 2 wt%. Based on the finished feed pro¬ duct, the amount of emulsifying agent is typically in the range of 0.05 to 1 wt% . It may be preferred to select an emulsifying agent which is solid at room temperature and having a relatively high melting point such as in the range of 50-60°C. It has been found that by incorporating such an emulsifying agent, the finished feed mixture particles when cooled to ambient temperature set relatively rapidly to provide solid, coherent feed particles which essentially do not disintegrate when administered to the fish breeding environments. It has been found that the incorporation of an emulsifying agent in the feed composition results in a feed mixture wherein the aqueous phase is evenly distributed in the feed composition as very small droplets which in turn results in less favourable conditions for microbial growth. This implies that the feed composition according to the invention in comparison with feed compositions prepared without the use of an emulsifying agent has an extended shelf life. It has e.g. been observed that it can been stored at a temperature within the range of 5 to 30°C and at low RH for up till six months without growth of fungi occurring on the surface of the particles. In contrast, conventional fish feed compositions kept under the same conditions frequently become mouldy. In useful specific embodiments of the invention, the feed composition contains a hydrocolloid such as a non-protein hydrocolloid, preferably a polysaccharide of vegetable or microbial origin. In this context, useful hydrocolloids include a gum such as e.g. guar gum, xanthan gum, gum arabic, LBG, gellan gum, a pectin, a carrageenan, an alginate, a starch including starch derivatives and a water soluble cellulose derivative such as CMC. In accordance with the invention, the feed composition may comprise further ingredients such as water soluble and water- insoluble vitamins, mineral components, flavouring agents or antioxidants such as e.g. ascorbic acid, ascorbyl palmitate, ascorbyl stearate, BHA (butylated hydroxyanisole) , BHT (buty- lated hydroxytoluene) , propyl gallate and tocopherols or preserving agents. A useful source of vitamins and mineral micronutrients is yeast cell mass either in the form a dry yeast or as a liquid yeast cell suspension, i.e yeast cream. In accordance with the invention, the feed composition can also be supplemented with pharmaceutically active substances. Such active substances typically include antibiotics, vaccines and substances which have a stimulatory effect on the immune system of the growing fish. Conveniently, the feed composition according to the present invention is in the form of pellets having a largest dimen- sion which is in the range of 1.5-20 mm, the size depending on the type and age of fish for which the feed is intended. In other embodiments, the fish feed composition according to the invention is in the form of granules having a largest dimension which is in the range of 0.2-2 mm. In a further aspect, the invention provides, as also men¬ tioned above, a method of preparing a fish feed composition, the method comprising as a first step the mixing of a lipid and an emulsifying agent. If it is required to melt the emulsifying agent, the lipid is pre-heated to a temperature above the melting point of the emulsifying agent e.g. to a temperature in the range of about 55-65°C. In a subsequent step, the protein source as defined above is added to the resulting mixture in the form of an aqueous suspension and/or solution or as a slurry of protein. The protein content of the aqueous suspension and/or solution may vary, but is preferably in the range of 10-90 wt%, such as 20 to 80 wt% protein, including a content of 30 to 70 wt% and e.g. from 40 to 60 wt% protein. The mixture resulting from the above subsequent step is then subjected to emulsifying conditions using a conventional homogenising or an emulsifying apparatus to obtain a water- in-lipid or a lipid-in-water emulsion, depending on the type of emulsifying agent used. Subsequently, the resulting emul¬ sion is formed into particles by a forming process e.g. pelleting at a temperature not exceeding 100°C and, if re¬ quired, the particles are dried e.g. using air drying, hot air drying, freeze drying or drum drying to obtain the feed composition. However, when a high melting emulsifying agent is used a drying step is generally not required to obtain solid and coherent feed particles. In a still further aspect, the invention relates to an alter¬ native method for preparing a fish feed composition which method comprises as a first step the preparation of an emul¬ sion comprising a lipid, an aqueous phase and at least one emulsifying agent. The aqueous phase may optionally contain protein in an amounts as mentioned above, i.e. in the range of 10-90 wt%, such as 20 to 80 wt% protein, including a content of 30 to 70 wt% and e.g. from 40 to 60 wt% protein. In a subsequent step, this emulsion is combined with at least one dry protein-containing ingredient to obtain a fish feed mixture which is subsequently formed and, if required, dried to obtain the fish feed composition. In either of the above methods, the aqueous suspension and/or solution may also contain at least one further structurizing or consistency controlling ingredient selected from a thick¬ ening agent, a viscosity enhancing agent and a stabilizing agent including as an example, a non-protein hydrocolloid such as a polysaccharide of vegetable or microbial origin, preferably a carrageenan or a gum, a wetting agent such as a ketone or an alcohol, preferably ethanol, a flavouring agent such as betaine, a mineral compound and/or a vitamin. In particular it has been found that the addition of a wet¬ ting agent including an alcohol or a ketone to the emulsion mixture facilitates an effective emulsification and subse¬ quent mixing with the other ingredients of the feed composi¬ tion. A suitable amount of an alcohol or ketone is 5-15 wt% of the emulsion and 1-5 wt%, calculated on the feed composi¬ tion after mixing. Evidently, part of an added alcohol or ketone will evaporate from the feed composition during mixing and storage of the finished feed composition. It is an important aspect of the methods according to the invention that the process temperature is low, whereby a deterioration of the dietary quality of the protein and lipid content is avoided and the energy consumption is low. Thus, the processes are preferably carried out at temperatures which are in the range of 10-100°C, preferably at the lowest possible temperatures where efficient mixing of the component can still be attained. Thus, the process temperature may preferably be within a range of 15-80°C such as a range of 20-60°C. A significant advantage associated with the feed composition according to the present invention is that it results in an increased metabolism or digestibility of proteins as compared to conventional fish feed. It has been found that in compari¬ son with a conventional carbohydrate-containing commercial feed, an increase of the growth rate or weight gain of the fish fed with the feed according to the invention in the order of at least 5 % can be obtained, such as at least 10%. Furthermore, the high content of lipid will provide a feed with a high energy content resulting in a lower requirement for feed per kg weight gain. It has been found that the feed intake per kg weight gain is reduced by at least 5% and possibly by at least 10%. The invention will now be described by way of illustration in the following non-limiting examples. EXAMPLE 1 Preparation of a fish feed composition 66.0 kg fish meal, 6.0 kg customized fish meal, 5.0 kg blood meal, 2.5 kg dry yeast and 0.75 kg mixture of vitamins and minerals were mixed under agitation to obtain a homogeneous dry fish feed ingredient mixture. 18.0 kg fish oil was heated under gentle agitation to about 60°C and 0.1 kg Lipodan PBS ® (emulsifying agent from Danisco Ingredients, Denmark, ve¬ getable oil based, containing about 20 wt% monoglyceride, dropping point about 62°C) was added and dissolved in the fish oil. 6.0 1 of water and 3.0 1 of ethanol were mixed and added slowly to the fish oil under agitation and emulsifying conditions until a homogenous and stable emulsion was obtained while keeping the temperature above 55°C. The emul¬ sion was applied through nozzles onto a rotating mixture of the dry fish feed ingredients. The resulting fish feed mix¬ ture had a loose, non-sticky/pasty consistency, which was readily formed into slightly soft pellets which hardened on cooling to ambient temperature. The resulting fish feed had the following composition (wt%) , based on the total weight of the fish feed: Water/moisture 7.0 EXAMPLE 2 Preparation of fish feed containing size. The process was carried out as described in Example 1, but the water was replaced by 6.0 kg of size. Analysis of the finished fish feed showed the following composition (wt%) , based on the total weight of the fish feed: EXAMPLE 3 Preparation of fish feed containing yeast cream 70.0 kg fish meal, 6.0 kg customized fish meal and 5.0 kg blood meal were mixed under agitation to obtain a homogeneous dry fish feed ingredient mixture. 14.0 kg fish oil was heated under gentle agitation to about 60°C and 0.12 kg Lipodan PBS ® was added and dissolved in the fish oil. 5.0 kg size, 5.0 kg liquid yeast cream, 0.75 kg of a mixture of vitamins and minerals were mixed with 3.0 1 ethanol and added slowly to the fish oil under agitation and emulsifying conditions until a homogenous and stable emulsion was formed, while keeping the temperature above 55°C. The emulsion was applied through nozzles onto a mixture of dry ingredients. The resulting fish feed mixture had a loose non-sticky/pasty consistency which could readily be formed into slightly soft pellets which hardened on cooling to ambient temperature. Analysis of the finished fish feed showed the following composition (wt%) , based on the total weight of the fish feed: Water/moisture 7.0 EXAMPLE 4 Preparation of fish feed from semi-manufactured ingredients 64.0 kg of semi-manufactured fish meal (not dried) , 8.0 kg semi-manufactured customized fish meal (not dried) , 5.0 kg blood meal, 5.0 kg liquid yeast, 0.75 kg of a mixture of vitamins and minerals and 6.0 kg size were mixed under agita- tion with 3.0 1 ethanol to obtain a wet fish feed mixture. 32.0 kg fish oil was heated under gentle agitation to about 60°C, and 0.3 kg Lipodan PBS ® was added and dissolved in the fish oil. The fish oil was slowly added under agitation to the mixture of wet ingredients. The resulting fish feed mixture had a loose non-sticky/pasty consistency and could readily be formed to slightly soft pellets which hardened on subsequent cooling to ambient temperature. Analysis of the fish feed showed the following composition (wt%) , based on the total weight of the fish feed: Water/moisture 7.0

Claims: CLAIMS 1. A dry fish feed composition for carnivorous fish, having a composition essentially corresponding to that of the natural prey for said fish, the feed comprising 30-70 wt% of protein, 20-50 wt% of lipid, 0-10 wt% of carbohydrates and a wetting agent and/or an emulsifying agent, the amounts of the compo¬ nents being based on the total weight of the feed. 2. A composition according to claim 1 wherein the combined content of protein and lipid is at the most 80 wt%. 3. A composition according to claim 1 or 2 wherein the carbo¬ hydrate content is at the most 8 wt%, preferably at the most 7 wt%, more preferably at the most 6 wt% such as at the most 5 wt%. 4. A composition according to claim 3 wherein the content of carbohydrate is at the most 2 wt%. 5. A composition according to claim 1, wherein the lipid content is in the range of 20-40 wt%. 6. A composition according to claim 1, wherein the lipid is selected from the group consisting of a vegetable lipid and a marine lipid. 7. A composition according to claim 6 wherein the lipid is a fish oil. 8. A composition according to claim 1 wherein the protein content is 40-65 wt%, preferably 45-60 wt% and more pre- ferably 50-60 wt%. 9. A composition according to claim 1 wherein the protein is a non-milk protein. 10. A composition according to any of claims 1-9 which comprises an emulsifying agent. 11. A composition according to claim 10 wherein the emulsi¬ fying agent is water-insoluble. 12. A composition according to any of claims 1-11 which further comprises a non-protein hydrocolloid. 13. A composition according to claim 12 wherein the hydro¬ colloid is a polysaccharide of vegetable or microbial origin. 14. A composition according to claim 1 which is in the form of pellets having a largest dimension which is in the range of 1.5-20 mm. 15. A composition according to claim 1 which is in the form of granules having a largest dimension which is in the range of 0.2-2 mm. 16. A method of preparing a composition according to claim 1, the method comprising (i) mixing a lipid and a wetting agent and/or an emulsi¬ fying agent, (ii) adding to said mixture the protein in the form of an aqueous suspension and/or solution, (iii) subjecting the resulting mixture to emulsifying conditions and (iv) subsequently forming the resulting emulsion into particles, which are subjected to cooling and, if required, drying to obtain the feed composition. 17. A method of preparing a fish feed composition according to claim 1, the method comprising the steps of (i) preparing an emulsion comprising a lipid, an aqueous phase and a wetting agent and/or an emulsifying agent, (ii) combining the emulsion with at least one dry fish feed ingredient to obtain a fish feed mixture, and (iii) subsequently forming the resulting emulsion into particles, which are subjected to cooling and, if required, drying to obtain the feed composition. 18. A method according to claim 17, wherein the aqueous phase contains a protein. 19. A method according to claim 17 wherein the weight ratio between the emulsion and the fish dry ingredient is in the range of 1:9 to 9:1. 20. A method according to claims 16 or 17 wherein the fish feed mixture contains at least one further ingredient selected from the group consisting of a non-protein hydro¬ colloid, a flavouring agent, a mineral compound and/or a vitamin. 21. A method according to claims 16 or 17, wherein the wetting agent is selected from the group consisting of an alcohol and a ketone.

Inventors: BECK-LAURITZEN PETER, BECK-LAURITZEN, PETER
Applicants: AQUATIC FEEDS APS, BECK LAURITZEN PETER, BECK-LAURITZEN, PETER
Application year: 1997
Main classification: A23K1
IPC codes: A23K1