METHOD AND FEED FOR REDUCTION OF THE CONTENT OF UNDESIRED NUTRIENTS IN THE WATER DISCHARGED FROM A FISH FARM

Abstract

A farming feed for fish in freshwater, wherein, in addition to the content of starch as an ordinary binder, there has been added to the feed up to 25 g per kg of constituent feed ingredients of a faecal binder of a non-starch type, and methods of making and using the same. The feed may be of a pressed or extruded type.

Claims

1. A method for reducing the content of undesired nutrients in water discharged from a fish farm, the method comprising the steps of: adding up to 25 g per kg of constituent feed ingredients of a non-starch faecal binder to the feed ingredients mixture for a farming feed of a pressed or extruded type comprising starch as a farming feed binder; and feeding said pressed or extruded farming feed to said fish, such that said non-starch faecal binder increases shear resistance of the said fish' faeces particles.

2. The method in accordance with claim 1, further comprising removing said faeces particles from said water discharged from said fish farm.

3. The method in accordance with claim 1, said farming feed comprising at least one faecal binder selected from the group consisting of algae meal, calcium alginate, guar gum and mixtures thereof.

4. The method in accordance with claim 1, said farming feed comprising a combination of two or more faecal binders selected from the group consisting of algae meal, calcium alginate, guar gum and mixtures thereof.

5. The method of claim 1 wherein said fish are salmonids.

6. The method of claim 1 wherein said discharged water is fresh water.

7. The method of claim 2 wherein said removing said faeces particles from said water discharged from said fish farm occurs by mechanical filtration.

8. A method for reducing the content of undesired nutrients in water discharged from a fish farm, the method comprising the steps of: formulating a farming feed for fish in freshwater, the farming feed being a dry, pelleted pressed feed or a dry, pelleted extruded feed, the farming feed comprising: starch as a pellet binder, and a non-starch faecal binder comprising up to 25 g per kg of constituent feed ingredients of an algae meal, a calcium alginate, or a guar gum, or mixtures thereof, wherein said non-starch faecal binder increases shear resistance of faeces particles from said fish; feeding said farming feed to said fish; and removing faeces particles from the water discharged from said fish farm.

9. The method in accordance with claim 8, the farming feed comprising a combination of two or more of the non-starch faecal binders selected from the group consisting of algae meal, calcium alginate and guar gum or mixtures thereof.

10. The method of claim 8, wherein the content of algae meal is from 1 to 20 g per kg of the constituent feed ingredients.

11. The method of claim 8, wherein the content of algae meal is from 1 to 5 g per kg of the constituent feed ingredients.

12. The method of claim 8, wherein the concentration of calcium alginate is from 5 to 15 g per kg of constituent feed ingredients.

13. The method of claim 8, wherein the concentration of calcium alginate is from 8 to 12 g per kg of the constituent feed ingredients.

14. The method of claim 8, wherein the concentration of guar gum is from 1 to 10 g per kg of constituent feed ingredients.

15. The method of claim 8, wherein the concentration of guar gum is from 1 to 5 g per kg of constituent feed ingredients.

16. The method of claim 8, the farming feed further comprising at least one member selected from the group consisting of oils, vitamins, minerals and mixtures thereof.

17. The method of claim 8, said starch pellet binder comprising at least one member selected from the group consisting of whole wheat, wheat flour, potato starch, corn starch, and tapioca.

18. The method of claim 8, wherein said fish are salmonids.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1A illustrates the faeces from trout fed a basic diet, the faeces having been collected by dissection of the intestinal tract;

[0029] FIG. 1B illustrates the faeces from trout fed the basic diet with the addition of guar gum as a faecal binder, the faeces having been collected by dissection of the intestinal tract;

[0030] FIG. 2A illustrates the viscosity and elasticity modules in faecal samples from trout, according to Experiment 1;

[0031] FIG. 2B illustrates the viscosity and elasticity modules in faecal samples from trout, according to Experiment 2;

[0032] FIG. 3A illustrates volume-dependent cumulative size distribution of suspended particles after disintegration by defined hydromechanical load of Experiment 1;

[0033] FIG. 3B illustrates volume-dependent cumulative size distribution of suspended particles after disintegration by defined hydromechanical load of Experiment 2;

[0034] FIG. 4A illustrates particulate content of nitrogen in suspended solids with increasing particle size after washing for 1 hour (average+standard deviation); and

[0035] FIG. 4B illustrates particulate content of phosphorus in suspended solids with increasing particle size after washing for 1 hour (average+standard deviation).

DETAILED DESCRIPTION OF THE INVENTION

[0036] While this invention may be embodied in many different forms, there are described in detail herein specific embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated

[0037] All published documents, including all US patent documents, mentioned anywhere in this application are hereby expressly incorporated herein by reference in their entirety. Any copending patent applications, mentioned anywhere in this application are also hereby expressly incorporated herein by reference in their entirety.

[0038] Faecal binders may affect the viscosity, elasticity and structural stability of feed substances during digestion and defecation. The addition of faecal binders to a fish feed may also be used to adjust the stability of faecal particles when these are in water. For this purpose only very small amounts of one or more indigestible binders are required, as these will concentrate during digestion and achieve their active concentration the furthest out in the intestinal tract. This is advantageous for biological reasons, as negative effects on digestibility are prevented or minimized.

[0039] Based on these effects, the addition of certain faecal binders to farming feed for freshwater fish, especially salmonids, will bring about an increase in the hydromechanical stability of the faecal particles, that is to say that the particles will, to a greater degree, resist the disintegrating effect of the water movement as the shear resistance increases. Increased shear resistance reduces the disintegration of the particles when they are exposed to shear forces. That is to say that when particles of different shear resistance are subjected to the same hydromechanical load, stabilized particles will maintain a larger dimension. Big particles will more efficiently be separated by mechanical treatment in, for example, a filter or sedimentation basin. In addition, a larger portion of the total content of nutrients will be bound in the particles because leakage from larger particles is reduced due to a reduced water contact surface.

[0040] Thus, the invention relates to a farming feed for fish in freshwater, the feed being of a pressed or extruded type and containing starch as an ordinary binder, there being added to the feed up to 25 g per kg of constituent feed ingredients of a faecal binder of a non-starch type.

[0041] Examples of suitable faecal binders of a non-starch type include, but are not limited to, algae meal, calcium alginate and guar gum.

[0042] The concentration of algae meal is advantageously from 1 to 20 g per kg of constituent feed ingredients, more advantageously from 1 to 5 g per kg of constituent feed ingredients.

[0043] The concentration of calcium alginate is advantageously from 5 to 15 g, more advantageously from 8 to 12 g per kg of constituent feed ingredients.

[0044] The concentration of guar gum is advantageously from 1 to 10 g, more advantageously from 1 to 5 g per kg of constituent feed ingredients.

[0045] The faecal binder of a non-starch type is alternatively a combination of two or more of the binders in the group consisting of algae meal, calcium alginate and guar gum.

[0046] The invention also includes a method for reducing the content of undesired nutrients in discharge water from a fish farm, wherein there is added to the feed ingredients mixture for a farming feed of a pressed or extruded type and containing starch as an ordinary binder, an addition of up to 25 g per kg of constituent feed ingredients of a faecal binder of a non-starch type; the fish is fed the pressed or extruded farming feed and the faeces are removed from the fish farm.

[0047] Examples of suitable faecal binders include, but are not limited to, algae meal, calcium alginate and guar gum.

[0048] In some embodiments, the faecal binder is a combination of two or more of algae meal, calcium alginate and guar gum.

[0049] “Constituent feed ingredients” refers to the actual amounts of different raw material ingredients on a wet weight basis, including fats like fish oil and vegetable oil, that are included in the feed mixture for the production of the pressed or extruded feed, before a possible, necessary addition of water for the pressing or extrusion process and before a possible, necessary removal of water in the drying process following the pressing or extrusion process. The term “feed ingredients mixture” refers to the same conditions as described for “constituent feed ingredients”.

[0050] The following non-limiting examples are further illustrative of the invention.

EXAMPLES

Materials and Methods

Diets and Faecal Binders—Preliminary Experiments

[0051] In the preliminary experiments the basic diet is compared with different treatments, in which different binders in certain concentrations have been added to a basic diet. The following binders were used: Lignin sulphonate, algae meal, modified (non-gelatinized) starch, calcium alginate, fish gelatine, guar gum, solid starch and cellulose powder.

[0052] The diet was given to groups of rainbow trout for minimum 5 weeks. Extruded feed of a 3.0 mm or 4.5 mm pellet size was used. The basic diet compositions were comparable with feed mixtures of ordinary commercial goods. By dissection faecal samples were removed from the lower part of the rectum, and macroscopic examinations of these and of faeces deposited at the bottom of the vessel, and sedimentation experiments carried out in Imhoff cones were used in order to find the effects of binders on the stability of the faecal particles. Apparent digestibility (raw protein, raw lipid), specific growth and utilization of feed were measured in order to find possible negative effects of binders on the feed quality.

[0053] The faecal binder concentrations that gave the most stable faecal particles without affecting digestibility, growth and feed absorption, were used in the further two feeding experiments.

Rainbow Trout Farming

[0054] Rainbow trout (Oncorhynchus mykiss, all females of the Hofer stock) were fed in circular green fibreglass vessels (diameter 1 m, height 0.7 m) with a water volume of 0.5 m.sup.3. The fish were of a conventional, unspecified microbiological status. Fish-pathogen-free water was provided from a groundwater well. Inflowing water was treated by aeration with small bubbles to remove elementary nitrogen and carbon dioxide as well as to add oxygen until near saturation. The water was supplied to each vessel through a vertical PVC inlet pipe at a 45° angle. The inlet was tangentially oriented near the wall of the vessel to provide a slightly circular flow, in which the fish could orientate. The self-cleaning form of the vessel provided for all the faeces to be carried to a central drain, which was covered with a perforated plate (plate diameter 0.2 m with a hole diameter of 0.01 m). It was, therefore, unnecessary to clean the vessels. The water flow rate was adjusted to 7-9 l/min. The vessels were lit daily for 12 hours (between 0700 and 1900) without dusk. Oxygen content (±0.1 mg O.sub.2/l), pH (±0.1) and temperature (±0.1° C.) was measured daily 1½ hour after manual feeding at the water inlet. The water parameters were measured in accordance with the German standard method of analyzing water, wastewater and slurry (modified in accordance with Gewasserschutzkommission, Dem Bodensee in den Abflussjahren 1996 und 1997 zugefiihrte Stofffrachten, p. 42. Internationale Gewasserschutzkommission f r den Bodensee, 2000), carried out as described above, but only in the beginning and closing of each experiment. The water parameters were all within the recommended area for rainbow trout farming. The average figures were:

TABLE-US-00002 Parameter Experiment 1 Experiment 2 Oxygen (mg/l) (pt) 8.1 7.8 pH (pt) 8.1 8.1 Temperature ° C. 11.7 13.2

TABLE-US-00003 Experiments 1 and 2 Earth Buffer alkaline NH.sub.4—N NO.sub.2—N NO.sub.3—N Chloride Sulphate PO.sub.4—P Conductivity capacity ions (ug/l) ug/l) (ug/l) (mg/l) (mg/l) (μg/l) (μS/cm) (mmol/l) (mmol/l) 164.8 2.6 1889 7.4 18.8 72 580 6.5 19.7

[0055] In Experiment 1 a total of 75 trout per vessel were fed experimental diets, and in Experiment 2 a total of 99 trout per vessel were fed experimental diets. For the different experiments, groups of trout were selected, anaesthetized and killed (n=15, 25 or 30 per vessel). Initial average weight of the trout in Experiment 1 was 184 g and in Experiment 2 the average weight of the trout was 191 g.

Feeding and Diet Composition

[0056]

TABLE-US-00004 TABLE 2 Faecal binders used Characteristics Product (solubility*, Faecal specifi- viscosity, gel Price Quantity binder cation strength*, digestibility) level added Algae ALGIBIND Soluble in cold water, Low 0.1-2% meal (p.c. low viscosity, low 5221025), gel strength, Algae a.s. partially digestible Calcium ALGINATE Soluble in cold water, High 1% alginate (Scogin HV medium viscosity, Alginate- medium 2205000, FMC gel strength, BioPolymer indigestible Guar gum Soluble in cold water, very Medium 0.1-1.0% high viscosity, high gel strength, indigestible *Concentration-dependent viscosity and gel strength according to information from distributor.

[0057] The fish were fed 1.2% of their body weight six days per week (Monday to Saturday). About 40% of the daily ration was given manually under continuous observation of behaviour at intervals between 0730 and 0900. The remaining feed was given by means of a feeding machine that fed continually until 1800. With this feeding pattern the initial experiments gave excretion of faeces at about 1000.

[0058] Six diets were formulated (see Table 2). They differed from each other only in the content of faecal binder. The diets all contained the same amounts of protein and energy. They contained balanced levels of amino acids, fatty acids, vitamins and minerals and are above recommended levels (Council N.R.: Nutrient requirements of fish, Committee on Animal Nutrition, Board of Agriculture, 1993). The faecal binder was added as dry powder to the other dry ingredients before extrusion of the mass. The diets were extruded (maximum values at the extruder matrix 120° C., 22 bars) with a diameter of 4.5 mm.

The basic diet contained per kg of feed:

TABLE-US-00005 Fish meal 305.09 g Semi-concentrate soy (Hamlet protein): 200.00 g Corn gluten: 192.80 g Wheat 122.23 g Monocalcium phosphate.sup.a:   6.61 g Fish oil: 168.00 g Mineral mixture.sup.b:   2.35 g Vitamin mixture.sup.c:   2.35 g Lycine HCl:   3.00 g Carophyll pink:   0.60 g Yttrium oxided.sup.d:   0.10 g .sup.aAvailable phosphorus 4.71 g/kg. .sup.bThe mineral mixture contained: calcium 150 g/kg, magnesium 8000 mg/kg, potassium 120 mg/kg; iron 10000 mg/kg, zinc 35000 mg/kg, manganese 4000 mg/kg, copper 800 mg/kg, selenium 25 mg/kg, iodine 50 mg/kg. .sup.cThe vitamin mixture contained: Vit A 550000 IU/kg, Vit D 420000 IU/kg, Vit E 45000 mg/kg, Vit K 2500 mg/kg, Vit B1 2200 mg/kg, Vit B2 4100 mg/kg, Vit B6 4500 mg/kg, Vit B5 13000 mg/kg, Niacin 15000 mg/kg, Folate 900 mg/kg. .sup.dYttrium oxide was added as a marker for measuring digestibility.

TABLE-US-00006 TABLE 3 Addition of a faecal binder to the experimental diets Diet Diet Diet Diet Diet Diet Faecal Unit of 1 2 3 4 5 6 binder measurement BD GG 0.1 GG 0.3 AB1 AB2 AT1 Guar gum g/kg 1.00 3.00 — — — (GG) Algibind g/kg — — — 3.00 6.00 — (AD) Alginate g/kg — — — — — 10.00 (AT)

Digestibility, Specific Growth, Utilisation of Feed

[0059] For digestibility measurement 54 trout per treatment in Experiment 1 and 75 trout per treatment in Experiment 2 were anaesthetized with clove oil (concentration 0.1 ml/l, time of exposure approximately 1 min.) and faeces were removed from the anal orifice. The faeces were frozen immediately in cryogen, freeze-dried and homogenized.

[0060] The content of dry substance, protein, fat, phosphorus and yttrium oxide was determined. The digestibility of protein, fat and phosphorus of the different diets was estimated.

[0061] The dry substance content was determined as the ratio of wet weight and dry weight after freeze-drying. Raw protein was analyzed in accordance with the EU Commission Directive 93/28/EEC (the Kjeldahl method), but with selenium as catalyst. Raw lipid was analyzed according to the EU Commission Directive 84/4EEC (method B), but with diethyl ether as the solvent. Phosphorus and yttrium were determined externally (Jordforsk, Ås, Norway). To the samples were added 10 ml of 6M nitric acid (p.a.) and 0.5 ml of hydrogen peroxide (p.a.) in a microwave oven and diluted with distilled water. Finally the samples were analyzed in an ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer). The wet weight of the fish was determined individually (±1 g) right after killing for the subsequent samples of dissected faeces. Specific growth rate was determined as:

[00001]$\mathrm{SGR}\left[\%\right]=100*\frac{{\ln }_{\left(\mathrm{fishing}\mathrm{weight}\right)}-{\ln }_{\left(\mathrm{starting}\mathrm{weight}\right)}}{T_{\left(\mathrm{finishing}\mathrm{date}\right)}-t_{\left(\mathrm{start}\mathrm{date}\right)}}$

The feed conversion rate was calculated as

[00002]$\mathrm{FCR}=\frac{\mathrm{Feed}\left[\mathrm{kg}\right]}{\mathrm{Growth}\left[\mathrm{kg}\right]}$

The Collecting of Faecal Samples

[0062] For rheology and particle size recording certain groups of trout were taken from each vessel, anaesthetized with clove oil (0.1 ml/l, 1 min.) and killed by a blow to the head. The faecal particles nearest to the anal orifice were removed by dissection. Only clearly mucus-covered faecal particles were used. The faeces were placed in aluminium dishes, hermetically sealed with a plastic film in order to prevent dehydration, and then cooled to 4° C. to slow down microbial decomposing processes. All measuring was finished within 8 hours after dissection. Faeces and intestines were examined macroscopically to detect irritated mucous membranes in the intestines, exudative enteritis (running intestinal inflammation) and hemorrhoid enteritis (bleeding intestinal inflammation).

Rheological Measurement

[0063] For rheological measurement 15 trout (Experiment 1) and 25 trout (Experiment 2) were picked out as above. Depending on the size, three to four faecal particles (necessary volume per measuring≈3 cm.sup.3) were combined and transferred to a rheometer (Paar Physica UDS 200). The applied measuring method was MP 313 (plate diameter 50 mm, 0°) with a gap of 1 mm. The shear load factor was 2.0371833 and the shear rate factor was 2.6179939. Measuring time was 12 seconds. In the time recording there was used a deformation with an amplitude of γ=60% at a frequency of 1 Hz. For frequency recording there was used a deformation with an amplitude of γ=40% at frequencies of 50; 32.1; 20.6; 13.2; 8.47; 5.43; 3.49; 2.24; 1.43; 0.92; 0.59; 0.38; 0.24; 0.16 and 0.10 Hz. Measuring time was 30 seconds. The temperature in the experiment unit was set at 4° C. and air moisture was adjusted to 100% saturation. All measurements were checked for deformation. Each measurement started with a time sweep of 50 single deformations, followed by frequency sweep after a 60 second delay.

Particle Size Distribution

[0064] For particle size measuring 15 trout (Experiment 1) and 30 trout (Experiment 2) were picked out as above. First faecal particles from the control, having a weight of 2 g, were broken under prescribed conditions until they showed the same particle size distribution (PSD) as observed in discharge water from trout farms. This was carried out by a method in which turbulence is provided by a constant flow of air from below in 2 l of distilled water. The predetermined setting, that is to say 0.05 MPa and exposure time of 8 minutes, was used in all the experiments. The amount of faeces was 2 g (+0.01 g) wet weight for Experiment 1 and 3 g (+0.01 g) wet weight for Experiment 2. The particle size measuring was carried out with the use of a non-invasive laser particle sizer (GALAI: CIS-1) equipped with a flow control (GALAI: LFC-100) and a flow-through cell (GALAI: GM-7). As the upper measuring limit for a laser particle sizer is 600 μm, all values were corrected by the percentage of particles larger than 600 μm. This value was determined by the use of a sieve.

Results

Experiment 1

Digestibility, Specific Growth Rate, Utilization of Feed

[0065] Specific growth rate was 1.13%±0.069% (average vessel mean±standard deviation). [0066] Average feed conversion rate was 0.90±0.046. [0067] At the end the average weight was 257 to 292 g. [0068] No macroscopically determinable traces of faecal binder could be pointed out in the intestinal tract. [0069] In up to two individuals per treatment slight intestinal irritation (rubor) was observed, but this was also observed in the control groups. [0070] Three individuals fed different diets showed presence of hemorrhoid enteritis. [0071] The faecal binder did not affect the observed digestibility of protein, lipid and phosphorus (see Table 4).

TABLE-US-00007 TABLE 4 The effect of faecal binder treatment on the digestibility coefficient (%) of protein, lipid and phosphorus. Feed Protein Lipid Phosphorus Basic diet 87.2% 90.1% 48.2% +Guar gum (0.1%) 87.3% 91.6% 47.9% +Guar gum (0.3%) 85.6% 89.0% 51.0% +Algibind 86.9% 92.5% 47.0% (0.3%) +Algibind 86.6% 90.7% 53.3% (0.6%) +Alginate (1.0%) 88.3% 90.8% 56.5%

Rheological Measurement

[0072] At least three repetitions were carried out. The measurement of the guar gum (0.1%) treatment gave incorrect values because of an error in the control program of the rheometer. These measurements were removed from the analysis.

[0073] The addition of all faecal binders used gave a significant improvement in the viscosity and the elasticity modulus in faeces from fish (FIG. 2A, Table 5). This is the clearest in Experiment 1. The basic diet in Experiment 1 gave less stable faecal particles than in Experiment 2 (FIG. 2A). Compared with the basic diet, guar gum led to the greatest increase in viscosity (183%) and Alginate lead to the greatest increase in the elasticity module (173%). In a combination of both visco-elasticity parameters guar gum gave the best result (155.5%) followed by Alginate (136%).

[0074] All visco-elastic functions show a weakening over time, which is the most evident for the elasticity module of the Alginate member.

[0075] Algibind is used in two different amounts in Experiment 1. The viscosity module as well as the elasticity module increased significantly with increased content.

TABLE-US-00008 TABLE 5 Adjusted average value for viscosity and elasticity modules in faeces from trout fed a basic diet or a basic diet with faecal binder added. Viscosity Elasticity module Diet Average Improved Average Improved Basic diet  38.6 Pas — 110.7 Pa — +Guar gum 109.3 Pas +183% 252.5 Pa +128% (0.3%) +Algibind 59.6 Pas  +54% 197.2 Pa  +78% (0.1%) +Algibind 72.4 Pas  +88% 235.2 Pa +112% (0.3%) +Alginate 77.4 Pas +100% 302.5 Pa +173% (1.0%)

Particle Size Distribution

[0076] All particle size distribution observed in faeces from fish fed diets containing a faecal binder showed increased particle size (see FIG. 3A). The effect on particle size was increased with an increase in the content of the respective faecal binder (FIG. 3A, Table 6). Guar gum gave the best improvement. In general the effect was more evident with increased particle size.

[0077] Table 6 shows the percentages of the total particle amount under 100 μm and under 600 μm, respectively, depending on treatment. Guar gum and Alginate resulted in a significantly smaller amount of particles under both sizes, whereas Algibind did not give the same effect. By means of the filtering potential connected with a suspension of these size characteristics, the effect on the content of particles in the discharge water may be calculated by proportionality. With the addition of guar gum (0.3%) the amount of particles up to the size of 100 μm in the discharge water was reduced by 40.2% and 600 μm by 24.6%, whereas for Alginate (1.0%) a reduction of 30.6% was found for the size 100 μm and 13.3% for 600 μm.

TABLE-US-00009 TABLE 6 The percentage of total particle volume under 100 μm and under 600 μm of suspended fish faeces particles from fish fed the same basic diet with different content of faecal binder. Improved = percentage improvement relative to basic diet in remaining waste load after filtering at 100 μm and 600 μm. At 100 μm At 600 μm Diet Cumulative % Improved Cumulative % Improved Basic diet 38.8 — 92.0 — +Guar gum 27.8 −28.3% 75.2 −18.3% (0.1%) +Guar gum 23.2 −40.2% 69.4 −24.6% (0.3%) +Algibind 36.3  −6.4% 90.4  −1.7% (0.1%) +Algibind 35.1  −9.5% 89.1  −3.2% (0.3%) +Alginate 26.9 −30.6% 79.8 −13.3% (1.0%)

Experiment 2

Digestibility, Specific Growth Rate, Utilization of Feed

[0078] Specific growth rate was 1.11%±0.082% (average vessel mean±standard deviation). [0079] Average feed conversion rate was 0.73±0.026. [0080] At the end the average weight was 417 to 490 g. [0081] None macroscopically determinable traces of faecal binder could be pointed out in the intestinal tract. [0082] In up to two individuals per treatment slight intestinal irritation (rubor) was observed, but this was also observed in the control groups. [0083] Three individuals fed different diets showed presence of hemorrhoid enteritis. [0084] The faecal binder did not affect the observed digestibility of protein, lipid and phosphorus (see Table 7).

TABLE-US-00010 TABLE 7 The effect of faecal binder treatment on the digestibility coefficient (%) of protein, lipid and phosphorus. Feed Protein Lipid Phosphorus Basic diet 89.7% ± 0.17% 95.7% ± 0.25% 46.7% ± 0.23% +Guar gum 89.1% ± 0.23% 94.6% ± 0.45% 51.5% ± 0.90% (0.3%) +Alginate 89.4% ± 0.09% 95.98% ± 0.13% 50.4% ± 0.36% (1.0%)

Rheological Measurement

[0085] At least nine repetitions were carried out. The measurement of the guar gum (0.1%) member gave incorrect values because of an error in the control program of the rheometer. These measurements were removed from the analysis.

[0086] The addition of all faecal binders used gave a significant improvement in the viscosity and the elasticity modulus in faeces from fish (FIG. 2B, Table 8). This is more evident in Experiment 1 than in Experiment 2. The basic diet gave in Experiment 2 more stable faecal particles than in Experiment 1 (FIG. 2B). Compared with the basic diet, guar gum lead to the greatest increase in viscosity (140%) and Alginate lead to the greatest increase in elasticity module (125%). In a combination of both visco-elasticity parameters guar gum gave the best result (108.5%) followed by Alginate (86.5%).

[0087] All visco-elastic functions show a weakening over time, which is the most evident for the elasticity module for the Alginate member.

TABLE-US-00011 TABLE 8 Adjusted average value for viscosity and elasticity modules in faeces from trout fed a basic diet or a basic diet with faecal binder added. Viscosity Elasticity module Diet Average Improved Average Improved Basic diet  49.4 Pas — 161.2 Pa — +Guar gum 118.3 Pas +140% 284.6 Pa  +76% (0.3%) +Alginate  72.5 Pas  +47% 362.6 Pa +125% (1.0%)

Particle Size Distribution

[0088] All particle size distribution observed in faeces from fish fed diets containing faecal binders showed an increased particle size (see FIG. 3B). The effect on particle size increased with an increase of the content of the respective faecal binder (FIG. 3B, Table 9). The reduced effect of faecal binder in Experiment 2 is in agreement with the corresponding reduced effect on the visco-elasticity parameters in Experiment 2. Guar gum gave the best improvement. The effect is less evident in Experiment 2 in which Alginate showed the best effect for particle size under 128 μm. Generally, the effect was more evident with increased particle size.

[0089] Table 9 shows the percentage of the total amount of particles under 100 μm and under 600 μm, respectively, depending on treatment. Guar gum and Alginate resulted in a significantly smaller amount of particles under both sizes, whereas Algibind did not give the same effect. By means of the filtering potential connected with a suspension with these size characteristics, the effect on the content of particles in the discharge water may be calculated by proportionality. With the addition of guar gum (0.3%) the amount of particles up to the size of 100 μm in the discharge water was reduced by 18.2% and 600 μm by 14.7%, whereas for Alginate (1.0%) a reduction of 23.3% was found for the size 100 μm and 2.9% for 600 μm.

TABLE-US-00012 TABLE 9 Percentage of total particle volume under 100 μm and under 600 μm of suspended fish faeces particles from fish fed the same basic diet with different content of faecal binder. Improved = percentage improvement relative to basic diet in remaining waste load after filtration at 100 μm and 600 μm. At 100 μm At 600 μm Diet Cumulative % Improved Cumulative % Improved Basic diet 35.1 — 93.4 — +Guar gum 28.7 −18.2% 79.7 −14.7% (0.3%) +Alginate 26.9 −23.3% 90.7  -2.9% (1.0%)

The Effect of the Particle Size on the Washing Process

[0090] Washing experiments with 125 faecal suspensions from an earlier experiment showed a significant increase in nitrogen and phosphorus content with increasing particle size (see FIG. 4), which indicates that larger particles have a greater potential for retaining these substances.

[0091] In order to investigate the washing effects of the faecal binder addition, the starting material of faeces must be identical with respect to dry weight and nutrient content. The dry weight of faeces from 75 trout per vessel was determined with one repetition per binder member. The dry weight of the control member (basic diet) was 11.4% (±0.2%) (average±standard deviation), for guar gum (0.3%) 11.6%±0.3%, and for Alginate (1.0%) 10.9%±0.1% without any statistically significant differences. Neither were there any significant differences in nutrient content.

[0092] For the control member and guar gum (0.3%) (n=15) and for Alginate (1.0%) (n=16) samples of 3 g of faeces were washed for 1 hour. The remaining solids showed no significant difference in the content of nitrogen or phosphorus (see Table 10). A significantly higher content of dry substance (+5%) and particulate phosphorus (+14.9%) could be observed in faeces from the guar gum member compared with the basic diet.

[0093] Alginate treatment showed no significant increase in the retention of solids in the form of dry substance, nitrogen or phosphorus compared with the control member (basic diet).

TABLE-US-00013 TABLE 10 Average values for remaining total of dry substance (TS), particulate nitrogen (N) and particulate phosphorus (P) after suspension of 3 g trout faeces samples for 1 hour in distilled water with different treatments (average ± standard deviation) TS NH.sub.4—N PO.sub.4 Diet [mg] Improvement [mg] Improvement [mg] Improvement P [%] N [%] Basic diet 236.9 ± — 6.452 ± — 7.717 ± — 3.3 ± 2.7 ± n = 15 4.4 0.205 0.265 0.89 0.94 +Guar gum 249.5 ± ±5.1% 6.324 ±  −1.9% 8.863 ± ±14.9% 3.3 ± 2.3 ± (0.3%); 3.3 0.328 0.353 0.12 0.12 n = 15 +Alginate 238.0 ± ±0.8% 5.524 ± −14.4% 7.872 ±  ±2.0% 3.6 ± 2.5 ± (0.1%); 3.0 0.184 0.219 0.76 0.76 n = 16

[0094] The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.