Feed for river-tracing spawning fish, preparation method thereof, method for improving seawater tolerance, growth and feed intake of river-tracing spawning fish, and use of fish feed for preventing or alleviating severity of cataract

Abstract

Fish feed for feeding river-tracing spawning fish in fresh water, comprising arginine in the form of free amino acids or dipeptides, histidine in the form of free amino acids or dipeptides in an amount of 0.1 to 7% by weight, and Na + in an amount of 0.2 to 5% by weight. The fish feed can be fed to the river-tracing spawning fish so as to promote growth in a fresh water and / or seawater stage, promote feed intake and / or prevent or relieve the severity of cataract.

Description

[0001] Feed for anadromous fish

[0002] The present invention relates to a feed for anadromous fish, a method of using the feed, and a method of preparing the feed.

[0003] Fish is an important source of protein for the world's population. It is recognised that per capita fish consumption should be increased due to its positive health effects.

[0004] However, it is no longer possible to increase the number of fish caught in the wild because of the impact on fish stocks. Some populations of wild fish have already collapsed, and for others, fishing must be reduced to make the population sustainable.

[0005] Aquaculture (fish farming) is therefore becoming increasingly important in supplying fish to the world's population.

[0006] Fish need protein, fat, minerals and vitamins to grow and stay healthy. This is especially important in the diet of carnivorous fish such as salmonids.

[0007] Initially in the farming of carnivorous fish, whole fish or ground fish were used to meet the nutritional requirements of farmed fish. Ground fish was mixed with various dry ingredients such as fish meal and starch, known as soft feed or semi-wet feed. With the industrialization of farming, soft feed or semi-wet feed was replaced by pressed dry feed. This in turn was gradually replaced by extruded dry feed.

[0008] Today, extruded feeds are almost universal in salmonid farming.

[0009] The main source of protein in dry fish feed is fishmeal of different qualities. Fishmeal and fish oil are obtained from so-called "industrial fish". The catch of industrial fish cannot be increased. For example, industrial fish can originate from Northern Europe or from South America, especially fish caught off the coast of Peru and Chile. The production in these countries fluctuates to some extent every year. The El Niño climate phenomenon occurs approximately every 7 years and severely reduces the production of industrial fish. This affects the availability of fishmeal and fish oil on the world market and the prices of these raw materials rise significantly.

[0010] The aquaculture industry, and in particular the fish feed industry, has for many years been predicting a shortage relative to future demand for both fishmeal and fish oil.

[0011] Other sources of animal protein are also used in dry fish feed. Thus, it is known that blood meal, bone meal, feather meal and other types of meal produced from other slaughterhouse wastes, such as poultry chicken meal, can be used. These are usually cheaper than fish meal and fish oil. However, in some geographic areas, such as Europe, restrictions have been imposed on the use of such raw materials in the production of feed for animals and fish used to produce food. Insect meal and proteins from microorganisms and microalgae biomass are also known to be used for this purpose, and in the future macroalgae may be used.

[0012] It is also known to use vegetable proteins such as wheat gluten, maize (maze, corn) gluten, soy products, lupin meal, pea meal, soybean meal, rapeseed meal, sunflower meal, distillers grains solubles (DDGS), fava bean products and rice flour. Soybean is a low-cost, high-protein raw material that is available in large quantities worldwide. Therefore, soybean has been used in fish feed for many years.

[0013] Therefore, there is pressure to minimize the amount of raw materials used in aquaculture fish feeds.

[0014] Furthermore, aquaculture is capital intensive. Investments are made in cages, pens or ponds, feeding automata, storage facilities and other infrastructure. There are also costs associated with the fish themselves, as they are purchased as fingerlings (such as trout and salmon species) or wild caught.

[0015] The most important single cost in aquaculture is the cost of feed. Labor costs are also important.

[0016] The selling price of the fish and the amount of fish caught determine the profitability of the operation.

[0017] A faster turnover has several positive results. First, it helps cash flow. Second, it improves risk management. Fish diseases are common and the likelihood of outbreaks is higher during a long growing season. There is also a risk that fish will escape unexpectedly, such as when moving nets or if fish pens are damaged by bad weather.

[0018] The turnover rate depends on how quickly the fish grows to a catchable size. For example, it takes 12 to 18 months or even 24 months to grow Atlantic salmon from smolt (the sea transfer stage, discussed in more detail below) to catchable size. The catchable size depends on the fish species and the market. Some markets prefer Atlantic salmon larger than 6 kg. Rainbow trout are sold in portions in some markets, weighing 300 g. The farming of larger rainbow trout is also being done.

[0019] Growth rate is expressed as a percentage of daily body weight gain (specific growth rate, SGR). Specific growth rate is calculated as follows:

[0020]

[0021] FinalW = Final weight

[0022] InitW = Starting weight

[0023] Days = time from measuring the initial weight to the final weight

[0024] SGR does not take into account the amount of feed fed to obtain growth. It is only a measure of growth rate. A high SGR depends on the digestibility of the raw materials and how optimal the feed composition is in terms of protein and fat ratio, amino acid composition and fatty acid composition. Trace components such as vitamins and minerals must also be present in sufficient amounts.

[0025] Therefore, it is desirable to produce fish feeds that result in good (high) SGR. High feed intake, body weight and weight gain are also desirable.

[0026] Salmonoids are anadromous fish that require special attention to their feed. Anadromous fish hatch in fresh water and spend the fry stage in fresh water, but after smoltification (i.e. reaching the physiological stage of young salmon when they can transfer from fresh water to sea water for the first time), they migrate to brackish water and possibly to sea water with full salinity. The fish return to fresh water to lay eggs. Salmonoids refer to species belonging to the family Salmonidae. Examples of salmonoids are salmonid species such as Atlantic salmon (Salmo salar) and trout species such as rainbow trout.

[0027] The juvenile transformation of anadromous fish involves behavioral, morphological, and physiological changes that are in preparation for migration and entry into marine waters and will enhance their success.

[0028] Silvering can be achieved in aquaculture by photomanipulation, i.e. lighting regimes. The traditional approach is the "winter signal", i.e. part of the day light and part of the day dark, e.g. about 12 hours of darkness per day and about 12 hours of light per day. However, compared to other lighting regimes, in particular 24:0, i.e. continuous lighting, the winter signal (i.e. keeping the fish in the dark for a period of time during the day) reduces feed intake and thus growth. It is desirable to develop other feeds and feeding methods to support feed intake and / or growth during the freshwater stage, e.g. using specific feeds.

[0029] WO02 / 30192 to Aquabio Products Sciences LLC (relating to a feed product called "SUPERSMOLT") discloses a silver whitening process which requires a feed containing sodium salts and a polyvalent cation receptor modulator (PVCR) and the addition of Ca to the water. 2+ and Mg 2+ ions. The preferred PVCR is tryptophan in the free amino acid form. Feeds containing histidine in the free amino acid form as the PVCR were tested but poor results were reported (Table 19). This document reviews the physiology of silvering.

[0030] WO2016 / 046182 to Europharma A / S (relating to a feed product called "SUPERSMOLT FeedOnly", which developed the earlier SUPERSMOLT work) discloses a fish feed that can be used for salmonid silvering and a method of preventing desmoltification, the fish feed comprising sodium, magnesium and calcium salts, and a polyvalent cation receptor modulator (PVCR), which may be tryptophan in the form of a free amino acid.

[0031] In commercial farming of salmon and rainbow trout, it is well known that when fish are ready for seawater as juveniles and are transferred from fresh water to seawater, they lose their appetite. This is a stressful period associated with high mortality rates. Fish can be depressed for several weeks after the transfer. For fish farmers, this means lost growth. It takes longer to grow fish to a size suitable for slaughter, especially since growth has a daily compounding effect. Therefore, in fish farming, there is a need for feeds that are easily accepted by fish that have recently been transferred to seawater.

[0032] WO2010087715 of the Applicant Group of Companies discloses a fish feed, wherein the fish feed is produced by extrusion and contains at least 3% by weight of arginine. Some of the arginine may be provided in the form of a free amino acid, for example by supplementing with 1% by weight of crystalline arginine. The feed is used to prevent growth reduction in salmonids when transferred from fresh water to sea water. The document contains a literature review of the arginine requirements of salmonids.

[0033] In addition, salmonid eyes are susceptible to cataracts (clouding of the lens and / or lens capsule). This leads to decreased vision and thus reduced feed intake. EP1199947 of BioMar Group discloses a salmonid feed for reducing cataracts, comprising at least 1.15% by weight of histidine. It is desirable to develop feeds and feeding methods, particularly for the freshwater stage, to reduce cataracts and / or support feed intake and / or growth in the saltwater stage, for example using specific feeds.

[0034] In a first aspect, the present invention relates to a fish feed for rearing anadromous fish in freshwater, comprising: arginine in free amino acid form or in dipeptide form, preferably in free amino acid form; histidine in free amino acid form or in dipeptide form, preferably in free amino acid form; and 0.2 wt% to 5 wt% Na + .

[0035] Preferably, the fish feed comprises 0.3 wt%-4.5 wt%, more preferably 0.4 wt%-4 wt%, still more preferably 0.6 wt%-3.5 wt%, for example 0.8 wt%-3 wt%, or 1 wt%-2.5 wt% of Na + .

[0036] Preferably, at least part of the Na + It is added to the feed in the form of NaCl, more preferably in the form of 1 wt%-10 wt%, or preferably 3 wt%-8 wt% NaCl.

[0037] The term "fish feed" as used herein includes compositions as described below. Typically, the fish feed comprises fish meal as an ingredient. Suitably, the fish feed is in the form of flakes or pellets, such as extruded pellets. Preferred pellet sizes (diameters) are 1.5-6 mm, such as 2-5.5 mm, 2.5-5 mm, 3-4.5 mm or 3.5-4 mm.

[0038] References to the amino acids arginine and histidine include the D and L isomers, racemic or non-racemic mixtures, and salts thereof, respectively. Preference is given to using L-arginine and L-histidine, or dipeptides or salts thereof.

[0039] Preferably, the stated amounts of arginine and histidine in free amino acid form or in dipeptide form are added amounts in addition to any contribution from raw materials (eg fish meal).

[0040] Preferably, each of arginine and histidine, either in free amino acid form or in dipeptide form, is synthesized and / or provided in a form with a purity exceeding 50%. Suitably, histidine may be provided in the form of histidine hydrochloride monohydrate.

[0041] Preferably, the fish feed comprises 0.5-7% by weight, preferably 0.6-5% by weight, more preferably 0.7-4% by weight, still more preferably 0.75-3% by weight, even more preferably 0.8-2% by weight, for example 1-1.5% by weight, of arginine in the form of a free amino acid or a dipeptide, preferably in the form of a free amino acid, and / or 0.1-7% by weight, preferably 0.15-5% by weight, more preferably 0.2-4% by weight, still more preferably 0.25-3% by weight, for example 0.3-2% by weight, or 0.35-1.5% by weight, of histidine in the form of a free amino acid or a dipeptide, preferably in the form of a free amino acid.

[0042] Typically, fish feed, especially in freshwater stages, contains fish meal. Fish meal contains Ca 2+ Ions and Mg 2+ ions. Tacon and Da Silva (Mineral composition of some commercial fishfeeds, available in Europe. Aquaculture. 1983, vol. 31: 11-20) provided an analysis of the mineral composition of 38 commercially available fish feeds. It was found that such feeds contained 2.5-37 g / kg of Ca 2+ ions, and 0.4-3.0 g / kg, preferably 1-2.5 g / kg of Mg 2+ ions. Suitably, the fish feed of the present invention may contain such conventional levels of Ca 2+ Ions and Mg 2+ ion.

[0043] In an embodiment, up to 1 wt% Ca is added to the feed above conventional levels. 2+ Salt and / or Mg 2 + Salt, preferably no Ca is added to the feed above normal levels 2+ Salt or Mg 2+ Salt.

[0044] In a preferred embodiment, the fish feed comprises 0.75 wt% to 1.5 wt% of arginine in free amino acid form or in dipeptide form, preferably in free amino acid form, 0.25 wt% to 0.75 wt% of histidine in free amino acid form or in dipeptide form, preferably in free amino acid form, and 1 wt% to 3 wt% of Na + .

[0045] Preferably, the anadromous fish is a salmonid, more preferably a salmon, such as Atlantic salmon.

[0046] Salmonids are so-called oily fish. They need a high-fat diet to stay healthy. They deposit fat in their fillets. Generally speaking, they can use most of the fat in the feed to obtain energy, while the protein in the feed is deposited in the muscle tissue. This means that a large part of the protein supplied is used for growth. This is advantageous because it provides a favorable ratio between the feed used and the marketable product. Therefore, preferably, the fish feed contains at least 15% by weight of lipids, more preferably at least 20% by weight of lipids, such as 20% to 40% by weight, 20% to 35% by weight, or 20% to 30% by weight of lipids. The preferred range is 20% to 35% by weight of lipids.

[0047] Preferably, the fish feed contains a protein level of 30 to 60 wt%, preferably 35 to 55 wt%, more preferably 36 to 54 wt%, even more preferably 37 to 53 wt%, still more preferably 38 to 52 wt%, or 39 to 52 wt%, for example 40 to 52 wt%.

[0048] In a preferred embodiment, the fish feed has an approximate composition of 30-50 wt% protein, 3-15 wt% moisture and lipids as described above.

[0049] When comparing the nutritional content of different feeds and feed types, it is important to consider moisture content. For pressed and extruded feeds, in commercial settings and in many scientific papers, feed composition is often stated on an "as is" basis, an approach also used in this paper. For feeds containing large and / or varying amounts of water, composition is often stated on a dry matter basis.

[0050] Preferably, the fish feed comprises one or more of the following:

[0051] - Sources of protein, carbohydrates and lipids, discussed in more detail below;

[0052] - optionally a binder (e.g. starch; suitable sources are wheat, potato flour, tapioca, bean, pea starch, barley and corn starch)

[0053] - Vitamin premixes;

[0054] - mineral premixes; and

[0055] - Pigments (e.g. canthaxanthin, astaxanthin; mixed pigment sources may be used);

[0056] -Optionally other functional ingredients such as immunostimulants, palatability enhancers, feces binders.

[0057] Suitable sources of protein, carbohydrates and lipids include:

[0058] -Fishmeal and fish oil

[0059] - Krill meal and krill oil

[0060] - Microalgae and macroalgae

[0061] - Animal meals (e.g. blood meal, feather meal, poultry meal such as chicken meal, bone meal, insect meal and / or other types of meal prepared from other slaughterhouse waste)

[0062] -Animal fats (such as poultry oil)

[0063] - Vegetable powders (e.g. soya powder, lupin powder, pea powder, soya meal, rapeseed powder, rice powder, flaxseed powder, sunflower seed powder)

[0064] - Vegetable oils (e.g. rapeseed oil, soybean oil, linseed oil, sunflower oil)

[0065] -Gluten (such as wheat gluten or corn gluten)

[0066] - Further added amino acids (e.g. lysine, methionine)

[0067] In addition, some suitable sources of protein, carbohydrates and lipids are discussed in the Introduction.

[0068] The fish feed is preferably prepared by a method comprising the following steps:

[0069] Combine ingredients in a mixer;

[0070] extrusion or compression of granules; and

[0071] The particles are coated with oil.

[0072] Preferably, the fish feed is extruded.

[0073] Both single screw and twin screw extruders are suitable. A cooking extrusion process is suitably used, generally as follows. The extruded material is a mixture of the above ingredients and water. The water can be added to the mixture in the form of water or steam. The mixture can be preheated in a so-called pre-processor, where the heating is carried out by adding steam to the mixture. Steam and water can also be added to the material in the extruder. In the extruder itself, the pasty material is pushed by the screw to the constriction at the outlet end of the extruder and further formed into the desired cross-sectional shape by a die plate. On the outside of the die plate, a rotating knife is usually placed to cut the string coming out of the die hole into the desired length. Usually, the pressure outside the die plate will be equal to the ambient pressure. The extruded product is called extrudate. Due to the pressure generated inside the extruder and the steam added to the material, the temperature may exceed 100°C, and the pressure in the material will be higher than atmospheric pressure before being extruded out of the die opening.

[0074] Cooking extruded starchy material causes the starch granules to swell, so that the crystalline starch in the granules is released and can unfold. This is called gelatinisation of the starch. The starch molecules form a network that helps to hold the extrudate together. In particular in feeds for carnivorous fish, starchy raw materials are added due to their properties, acting as a binder in the finished fish feed. The natural prey of carnivorous fish does not contain starch. Carnivorous fish have few or no digestive enzymes that can convert starch into digestible sugars. Cooking of starch makes it more digestible. This is partly because the starch is no longer raw and partly because the cooking process begins to break the starch down into smaller sugar units that are more easily digestible.

[0075] Another effect of cooking extrusion is that the extrudate becomes porous. This is caused by the pressure drop at the die opening and the drop in temperature. The water in the extrudate immediately expands and is released in the form of steam, leaving a porous structure in the extrudate. This porous structure can be filled with oil at a later process stage. Extrusion feeds usually contain 18% to 30% water after extrusion. After extrusion, this feed undergoes a drying phase and a subsequent oil coating phase. The final product usually contains about 10% or less water and is therefore storage stable because the water content in such feeds is low, which prevents the growth of fungi and molds and also avoids bacterial decomposition. After oil coating, the feed is usually cooled and packaged.

[0076] The extrudate is therefore different from pressed feed. Pressed feed refers to feed produced by a feed press. This process differs from extrusion in many ways, generally as follows. Less water and steam are used in the process. The feed mixture is pressed through the die ring from the inside out by rollers rotating on the inside of the die ring. The temperature and pressure are lower than for extrusion and the product is not porous. An effect of this process is that the starch is not as easily digestible as after extrusion. Pressed feed will usually contain less than 15% water after pressing and possible oil application. Drying of pressed feed is usually not necessary, but post-treatment can be done. The feed is cooled before packaging.

[0077] Usually only one type of feed is fed, in which case each piece of feed should be nutritionally adequate. However, two or more types of feed can be used in combination.

[0078] In a second aspect, the present invention relates to a method for rearing anadromous fish in fresh water, which comprises rearing said fish with the above-mentioned fish feed during a rearing period.

[0079] As used herein, the term "fresh water" includes water having less than 3000 ppm of total dissolved salts (eg, less than 0.05 ppt of NaCl). As used herein, the term "fresh water" includes water having less than 1 ppt of total dissolved salts.

[0080] As described in the first aspect of the present invention, the fish is preferably salmonid, more preferably salmon, and most preferably Atlantic salmon.

[0081] Suitably, the feeding period is at least 250 day degrees, preferably at least 350 day degrees, for example at least 450 day degrees, or at least 550 day degrees, or at least 650 day degrees, more preferably at least 750 day degrees, or at least 850 day degrees, at least 950 day degrees, or at least 1000 day degrees. Preferably, the feeding period is 420-1008 day degrees.

[0082] As used herein, the term "degree day" (also referred to as "degree day") refers to the number of days multiplied by the average water temperature (°C). As used herein, the term "seawater" includes water of high salinity, such as brackish water. Seawater can include brackish water, such as 3 ppt to 30 ppt of dissolved salts, and seawater can include full concentration seawater of 30 ppt to 38 ppt of dissolved salts.

[0083] Suitably, the rearing period is at least 5 weeks, preferably at least 12 weeks. The rearing period preferably ends within a week before the fish are transferred to seawater, but may also end earlier, for example 5 weeks before the transfer. Alternatively, the rearing period may be until the fish are transferred to seawater. For an average water temperature of 12°C, 420 degrees Celsius corresponds to 5 weeks and 1008 degrees Celsius corresponds to 12 weeks.

[0084] An artificial winter signal may be applied during at least a portion of the rearing period, and / or a continuous light signal may be applied during at least a portion of the rearing period.

[0085] As used herein, the term "winter signal" refers to the use of any light / darkness other than full 24-hour light. Non-limiting examples of winter light signals are 6-12 hours of light and 18-12 hours of darkness per day, or 12-18 hours of light and 6-12 hours of darkness per day. A 12:12 winter signal is commonly used and is considered suitable. The light can be artificial light (artificial winter signal) or natural light (natural winter signal).

[0086] In a preferred embodiment, the artificial winter signal is applied initially and then the continuous light signal is applied. Preferably, the artificial winter signal is applied for 5-9 weeks, such as 7 weeks, and then the continuous light signal is applied for 3-7 weeks, such as 5 weeks.

[0087] In another preferred embodiment, a continuous light signal is applied throughout the feeding period.

[0088] Other aspects of the invention include:

[0089] - A method for improving seawater tolerance of anadromous fish, comprising raising said fish according to the method described above;

[0090] - a method for promoting the growth of anadromous fish in freshwater and / or marine stages, comprising raising said fish according to the above method;

[0091] - A method for improving feed intake of anadromous fish of the freshwater and / or marine stages, comprising raising said fish according to the method described above;

[0092] - a fish feed as described above, for preventing or reducing the severity of cataracts in fish, wherein the fish feed is optionally fed to the fish according to the method described above;

[0093] - A method for preparing a fish feed as described above, which method comprises mixing the ingredients and optionally extruding pellets of said fish feed, wherein said free amino acids are mixed into said ingredients and / or added by top coating.

[0094] As used herein, "promoting growth" means achieving better growth compared to fish not receiving the test diet.

[0095] Features described in relation to any aspect of the invention may be used in relation to any other aspect of the invention.

[0096] The invention will be further described with reference to non-limiting examples and accompanying drawings, in which:

[0097] Figure 1 The water and lighting scheme for this embodiment is shown.

[0098] Figure 2 The feed, water and lighting regimen for this example is shown.

[0099] Figure 3 Feed intake results for this example are shown (expressed as a percentage of body weight per day, and as cumulative feed intake).

[0100] Figure 4 The body weight results for this example are shown.

[0101] Figure 5 The weight gain results for this example are shown.

[0102] Figure 6 The specific growth rate (SGR) results for this example are shown.

[0103] Figure 7 Cataract results for this example are shown. Example

[0104] An experiment was conducted between November 2020 and May 2021 at the ARC Lerang Research Station in Skretting, Norway.

[0105] Atlantic salmon with an average starting weight of 40 g were distributed into 100 L experimental tanks, starting with 80 fish per tank, with 3 tanks per diet (24 tanks in total).

[0106] Feed type, water type and temperature, feeding frequency and lighting scheme are shown in Tables 1 and 2 and Figure 1 and Figure 2 Overall, there was a 3-month period in freshwater, followed by a transfer to seawater, and a 3.5-month period in seawater. Different light regimens were used for the first 7 weeks in freshwater (12:12 dark:light, i.e. winter signal; or 24:0 light, i.e. continuous light). Thereafter, all groups were under continuous light.

[0107] Feeding after the seawater transfer (when daily feed intake could not be determined) was targeted at 1.15% of body weight per day. Prior to the seawater transfer, daily feed intake was determined and is reported below.

[0108] The average final weight after 3.5 months in seawater was 381 g.

[0109] feed

[0110] The feed is prepared by extrusion. Arginine and histidine are added to the dry premix.

[0111] The feed used in the examples is shown in Table 1:

[0112] Table 1

[0113]

[0114]

[0115] *L-Histidine monohydrochloride monohydrate

[0116] The base formulations corresponded to the relevant control formulations with minimal necessary modifications.

[0117] The design of diet S+T+Ca+Mg was similar to the "SUPERSMOLT FeedOnly" feed described above.

[0118] Phase 1: Freshwater, 7 weeks, target weight range 40-90g, starting average fish weight 40g, final average fish weight 92g, 2mm diet

[0119] Ctrl 1——Control

[0120] Feed A - basic formula + 1.25 wt% arginine + 5 wt% NaCl

[0121] Feed S+H - basic formula + 0.5 wt% histidine hydrochloride monohydrate (0.37 wt% histidine) + 5 wt% NaCl

[0122] Feed S+A+H1 - basic formula + 1.25 wt% arginine + 0.5 wt% histidine hydrochloride monohydrate (0.37 wt% histidine) + 5 wt% NaCl (feed of the present invention)

[0123] Phase 2: Freshwater, 5 weeks, target weight range 90-120g, starting average fish weight 92g, final average fish weight 121g, 2mm diet

[0124] Ctrl 2 - Compare

[0125] Feed S+A+H2——Basic formula+1.25 wt% arginine+0.5 wt% histidine hydrochloride monohydrate (0.37 wt% histidine)+5 wt% NaCl (feed of the present invention)

[0126] Feed S+T+Ca+Mg - similar to "Supersmolt FeedOnly", containing 0.4 wt% L-tryptophan + 0.25 wt% MgCl2 + 0.75 wt% CaCl2 + 5 wt% NaCl (comparative example)

[0127] Phase 3: Seawater, 3.5 months

[0128] Ctrl SW diet in seawater for 3.5 months according to Table 2.

[0129] The approximate analysis of the feed is shown in Table 2:

[0130] Table 2

[0131]

[0132] Mortality was low in both the freshwater and seawater phases for all treatments, with no mortality in the first phase in freshwater (Phase 1), 1-2 fish per tank in the final phase in freshwater (Phase 2), no mortality in the first 6 weeks in seawater, and one dead fish per tank in weeks 7-12 in seawater (Phase 3). No statistically significant differences were observed between any of the treatments.

[0133] The daily feed intake results are as follows Figure 3 As shown. The scheme Ctrl 1 / S+A+H2 / 24:0 gave the best feed intake results in fresh water (1.14% of body weight per day), sea water (0.91% by weight of body weight), and fresh water and sea water combined (1.06% of body weight). These results are better than Ctrl 1 / S+T+Ca+Mg / 24:0 (1.12%, 0.76%, and 1.00% of body weight per day, fresh water, sea water, and combined, respectively). With an initial 12:12 light, the best scheme for feed intake was S+A+H1 / S+A+H2 (1.01% of total body weight per day). Ctrl 1 / S+A+H2 also performed well.

[0134] The results of cumulative feed intake were also similar. Figure 3 As shown. The regimen Ctrl 1 / S+A+H2 / 24:0 gave the best cumulative feed intake results in freshwater (3.153 kg in phase 1; 5.217 kg in freshwater overall) and seawater (8.375 kg in the first 6 weeks). These results were better than Ctrl 1 / S+T+Ca+Mg / 24:0 (3.145 kg, 5.068 kg, and 7.562 kg, respectively). The difference in cumulative feed intake was particularly large in seawater. In the initial 12:12 light regimen, S+A+H1 / S+A+H2 gave good cumulative feed intake results in seawater (7.324 kg).

[0135] Weight results are as follows Figure 4As shown. Starting from day 84, the regimen Ctrl 1 / S+A+H2 / 24:0 gave the best body weight results. These results were superior to Ctrl 1 / S+T+Ca+Mg / 24:0. With initial 12:12 light, the best regimen for body weight on the last day after 3.5 months in seawater was S+A+H1 / Ctrl 2. All the way through day 171, the regimen with initial 12:12 light generally performed as well as or better than Ctrl 1 / S+T+Ca+Mg with 24:0 light.

[0136] Weight gain results such as Figure 5 As shown. Similarly, Ctrl 1 / S+A+H2 / 24:0 gave the best growth results in fresh water (92.9 g total weight gain in fresh water) and sea water (282 g total weight gain in sea water). These results were better than the corresponding Ctrl 1 / S+T+Ca+Mg / 24:0 regimen (90.5 g and 265 g, respectively). The best regimen with an initial 12:12 light period was S+A+H1 / Ctrl 2: this regimen had a total weight gain of 79.2 g in fresh water and 261 g in sea water. In the first 6 weeks after transfer to sea water (days 85-127), the weight gain of regimen Ctrl 1 / S+A+H2 was 26% higher than the control (67 g vs. 53 g). This is important because, as mentioned above, growth is often poor during this critical post-transfer period.

[0137] Specific growth rate (SGR) results are as follows Figure 6 As shown. Similarly, Ctrl 1 / S+A+H2 / 24:0 gave the best SGR results in fresh water (1.48%) and gave better SGR than Ctrl 1 / S+T+Ca+Mg / 24:0 in the first 6 weeks after transfer to seawater (85-127 days) (0.97% vs. 0.87%). The regimen with initial 12:12 light and the diet of the present invention (Ctrl1 / S+A+H2; S+A+H1 / Ctrl 2; S+A+H1 / S+A+H2) performed well for seawater SGR. In the first 6 weeks after transfer to seawater (85-127 days), Ctrl 1 / S+A+H2 gave a 24% higher SGR than the control (1.03% vs. 0.83%). This is important because, as mentioned above, growth is often poor in this critical post-transfer stage.

[0138] Cataract results Figure 7As shown. Likewise, Ctrl 1 / S+A+H2 / 24:0 gave the best cataract results (79% of the fish had a cataract score of 0). These results were better than the corresponding Ctrl 1 / S+T+Ca+Mg / 24:0 regimen (34% of the fish had a cataract score of 0). The best regimen for starting 12:12 light was Ctrl 1 / S+A+H2: this regimen gave 67% of the fish a cataract score of 0. This compares favorably to the regimen using a histidine-containing feed, i.e. S+H / Ctrl 2 (44% of the fish had a cataract score of 0).

[0139] Results for the enzymatic NaK ATPase were evaluated. Freshwater gill samples were analyzed by Sintef Norlab, Norway. All three regimens of S+A+H2 in phase 2 (freshwater) produced high enzymatic activity results on day 84, just before the transfer to seawater. This indicates that the fish were ready for the transfer to seawater. These results were superior to the corresponding regimen of Ctrl 1 / S+T+Ca+Mg / 24:0. Good results were obtained with both lighting regimens; all fish were ready for the transfer to seawater.

[0140] This example shows that the freshwater Atlantic salmon feed of the preferred embodiment of the present invention achieves good and efficient growth (measured by feed intake, body weight, weight gain and specific growth rate) in both fresh water and sea water, timely silvering / good preparation for transfer to sea water, and avoidance of cataracts. Growth was particularly good during the critical 6 week period after sea water transfer. Good results were achieved under both the 12:12 and 24:0 initial light regimes. Feeding with the feed of the present invention immediately before sea water transfer gave good results. Results were comparable or better than the Ctrl 1 / S+T+Ca+Mg / 24:0 regimen.

[0141] Although the invention has been described with reference to preferred embodiments, it will be understood that various modifications may be made within the scope of the invention.

Claims

1. A fish feed for rearing anadromous fish in fresh water, comprising arginine in the form of a free amino acid or a dipeptide, 0.1% to 7% by weight of histidine in the form of a free amino acid or a dipeptide, and 0.25% to 5% by weight of Na + .

2. The fish feed according to claim 1, comprising 0.5 to 7 wt. %, preferably 0.75 to 2 wt. % arginine in the form of a free amino acid or a dipeptide, and / or 0.2 to 1.5 wt. % histidine in the form of a free amino acid or a dipeptide.

3. The fish feed according to claim 1 or 2, wherein the feed contains up to 1% by weight of Ca. 2+ Salt and / or Mg 2+ Salt, and wherein preferably no Ca is added to the feed 2+ Salt or Mg 2+ Salt.

4. A fish feed as claimed in any one of the preceding claims, comprising 0.6 to 1.25 wt% arginine in the form of free amino acids, 0.2 to 0.75 wt% histidine in the form of free amino acids and 1 to 3 wt% Na + .

5. Fish feed according to any one of the preceding claims, comprising at least 15 wt% lipids, preferably at least 20 wt% lipids, more preferably 20 to 35 wt% lipids.

6. Fish feed as claimed in any one of the preceding claims, wherein the fish feed is in the form of extruded pellets.

7. A method for rearing anadromous fish in fresh water, comprising feeding the fish with a fish feed during a rearing period, the fish feed comprising arginine in free amino acid form or in dipeptide form, histidine in free amino acid form or in dipeptide form, and 0.25 wt % to 5 wt % Na + , wherein the fish feed is optionally as described in any one of claims 1 to 6.

8. The method of claim 7, wherein the fish is salmonid, preferably salmon, more preferably Atlantic salmon.

9. The method of claim 7 or 8, wherein the feeding period is at least 250 days, preferably at least 650 days.

10. The method according to any one of claims 7 to 9, wherein an artificial and / or natural winter signal is applied during at least a part of the rearing period, and / or a continuous light signal is applied during at least a part of the rearing period.

11. A method as claimed in claim 10, wherein initially an artificial winter signal is applied and then a continuous light signal is applied.

12. The method of claim 10, wherein a continuous light signal is applied throughout the feeding period.

13. A method for improving seawater tolerance of anadromous fish, comprising raising the fish according to the method of any one of claims 7 to 12.

14. A method for promoting the growth of anadromous fish in freshwater and / or marine stages, which comprises raising said fish according to the method of any one of claims 7 to 12.

15. A method for promoting feed intake by anadromous fish in the freshwater and / or marine stages, comprising raising said fish according to the method of any one of claims 7 to 12.

16. A fish feed comprising arginine in free amino acid form or in dipeptide form, histidine in free amino acid form or in dipeptide form, and 0.25 to 5% by weight of Na + , for preventing or reducing the severity of cataracts in fish, wherein the fish feed is optionally as described in any one of claims 1 to 6, and the fish feed is optionally fed to the fish according to the method of any one of claims 7 to 12.

17. A method of preparing a fish feed as claimed in any one of claims 1 to 6, said method comprising mixing ingredients and optionally extruding pellets of said fish feed, wherein said free amino acids are mixed into said ingredients and / or added by top coating.

18. A method for preparing fish feed as claimed in claim 17, wherein the arginine and histidine in the form of free amino acids or dipeptides are synthesized and / or provided in a form with a purity of more than 50%.

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