Slow-sinking pellets or granules for fish farming 5 The present invention relates to slow-sinking pellets or granules for use in fish farming having a density greater than 1 g/cm 3 , obtainable by solvent-free melt extrusion of mixtures of one or more active components, customary matrix auxiliaries and a solid gas producer. The invention further relates to a process for 10 producing such pellets or granules. The production of solvent-free active compound formulations by the melt extrusion process is disclosed, for example, by EP-A 240 906 or EP-A 358 105. 15 EP-A 689 387 describes the production of fishfood by extrusion of fishfood-containing pellets which comprise polyvinylpyrrolidone as binder. Extruding a moist composition results in expansion of the pellets after extrusion due to evaporation of the liquid, 20 leading to a decrease in pellet density. According to US-A 4 393 087, floating fishfood pellets having a hardenable carbohydrate matrix are obtained which achieve their buoyancy by a content of expanded cereal particles. 25 US-A 5 171 588 discloses influencing the sedimentation rate of pellets for fish farming by using specific surfactants. However, the use of surfactants is disadvantageous with respect to 30 environmental problems. JP-A 4267852 describes pellets for fish farming which are obtained by extruding water-containing starch suspensions in the presence of an expansion means, such as sodium hydrogen carbonate 35 for example. In this process, the starch gelatinizes and the action of water and heat results in decomposition of the expansion means with formation of gas. The resulting forms are highly expanded and soft. 40 For the use of foods or food additives in fish farming, the floating or sinking behavior is of great importance. If the forms sink too rapidly, they are frequently removed too rapidly from the feeding range of many farmed fish, such as salmon or trout, for example, since material which has sunk to the bottom is no 45 longer eaten. This not only adversely affects the food intake, but rotting of the food on the bottom adversely affects the ecological equilibrium of the waters. Forms which float on the 2 surface are also not consumed by many types of farmed fish, however. It is an object of the present invention to find forms which have 5 a sedimentation rate which is favorable for use in fish farming. We have found that this object is achieved by the pellets or granules defined at the outset. 10 Biologically active substances for the purposes of this invention are veterinary drugs, in particular those which are suitable for use in fish farming, for example antibiotics, antimycotics, antihelmitics, antiparasitics, and in addition hormones and 15 growth promoters, as well as substances for immunostimulation, for example B-1,3-1,6-glucans, vitamins, such as vitamins C, E or A or their physiologically acceptable salts or esters, vitamins of the B series, carotenoids, such as 13-carotene, astaxanthin, canthaxanthin or zeaxanthin, for example, and in addition mineral 20 substances and/or trace elements. Any mixtures of said substance classes can also be used. The biologically active substances can be present in amounts of from 0.1 to 95, preferably from 5 to 70, particularly preferably.from 20 to 60, % by weight. 25 The biologically active substances are homogeneously distributed in a matrix of auxiliaries. As matrix auxiliary, at least one melt-processable binder is present. Suitable melt-processable binders according to the invention are celluloses or cellulose derivatives, such as cellulose ethers or cellulose esters, for 30 example hydroxyalkylcelluloses, such as hydroxypropylcelluloses, and in addition unsaponified or partially saponified poly(vinyl acetate) having Fikentscher's K values of from 10 to 150, preferably from 20 to 90, particularly preferably from 30 to 80, at 20 0 C measured in acetone (for determination of the K value, see 35 Fikentscher, Cellulosechemie 13 (1932) 58-64 and 71-74), poly(vinyl alcohol), homo- or copolymers of N-vinylpyrrolidone having Fikentscher K values in the range from 20 to 90, for example polyvinylpyrrolidone copolymers with vinyl esters such as vinyl acetate as comonomer, and also pectins, xanthans, guar gum 40 and carob gum, starches, starch derivatives, dextrins, polyfructosans, gelatin, carrageenans or mixtures of said binders. Also suitable are biodegradable polyesters as described in DE-A 44 40 858, for example polyesters based on butanediol, adipic acid and terephthalic acid. Preferably, poly(vinyl 45 acetate) or mixtures of poly(vinyl- acetate) and starch are used. The polymeric binders can be used in amounts of from 1 to 99.5, 3 preferably from 2 to 80, % by weight, particularly from 5 to 60% by weight. In addition, the matrix can contain, as auxiliary, meltable sugar 5 alcohols such as sorbitol, xylitol, mannitol, isomaltol or maltitol, or meltable sugars such as sucrose or glucose, or fats and waxes. These auxiliaries can be used in amounts of from 0 to 50% by weight. 10 The use of fillers such as chalk allows the sedimentation rate of the forms to be adjusted, depending on the application. Auxiliaries which are conventional for drugs or feed and food, 15 such as distintegrants, colorants, release agents, antioxidants, anticaking agents or sorbents, such as highly disperse silicon dioxide, for example, may also be added in the amounts customary therefor. 20 A gas producer in solid form is added to the pellets or granules according to the invention. Gas producers which are suitable according to the invention are alkali metal carbonates or alkaline earth metal carbonates such as sodium carbonate, potassium carbonate, magnesium carbonate or calcium carbonate, 25 and in addition, also, alkali metal hydrogen carbonates such as sodium hydrogen carbonate or potassium hydrogen carbonate. The gas producers are used in amounts of from 0.1 to 20, preferably from 1 to 10, particularly preferably from 2 to 5, % by weight. 30 The forms according to the invention preferably also comprise natural or synthetic flavorings, for example fish meal, fish meal hydrolyzates, soluble fish protein concentrates and hydrolyzates or other animal meal, or, in particular, fruit flavor mixtures, in amounts of from 0.1 to 20% by weight. 35 The pellets or granules according to the invention are produced by solvent-free melt extrusion. Solvent-free means that no water or organic solvents are added to the mixtures to be extruded. The 40 mixtures are processed, in particular, in single- or multi-screw extruders, preferably in twin-screw extruders. The components can be introduced as premix into the extruder, but the melt-processable binder, with or without other auxiliaries, can alternatively be melted first and the biologically active 45 substance can be added to the melt. This is advisable particularly when thermolabile biologically active substances are processed. The components are mixed in the extruder at temperatures in the range front 50 to 1800C, preferably from 80 to 4 1400C. All of the components may melt, or else only the melt-processable binders. The action of the shear forces in any case produces homogeneous mixing of all the components. Depending on the type of the biologically active substance, this can also 5 be present as a "solid solution", that is molecularly dispersed, in the matrix of auxiliaries. The term "solid solution" is known to those skilled in the art (see Chiou and Riegelman, J. Pharm. Sci. 60 (1971) (9), 1281 - 1301). 10 The melt is extruded through a dye or perforated plate and the still plastic composition is subjected to a shaping step. The shaping can be performed, for example, by calendering, cold-cut pelletization or, preferably, by hot-cut pelletization. 15 The granules or pellets obtained according to the invention have densities of from greater than 1 to 3 g/cm 3 , preferably from 1.1 to 1.8 g/cm 3 . By using a gas producer which completely or partly decomposes under the processing conditions, they have a porous or 20 film-structure. In contrast to conventional foams, they have a greater density, however. In water, the forms slowly sink. The sedimentation rates at 21 0 C in 4% strength aqueous sodium chloride solution are from 0.2 m/min to 10 m/min, preferably from 0.5 to 7 m/min, particularly preferably from 0.7 to 5 m/min. At these 25 sedimentation rates, there is an optimum consumption of the granules or pellets by the fish. The sedimentation rates can be specifically controlled by the amounts of added gas producer. The forms according to the invention are free of surfactants such as detergents. 30 The pellets or granules can have lengths of from 0.5 to 50 mm, preferably from 1 to 15 mm, and widths of from 0.2 to 20 mm, preferably from 1 to 10 mm. The particle size which is chosen in an individual case will also depend on the type of fish. 35 The pellets or granules are suitable in principle for all farmed fish or crustaceans, in particular for the farming of trout, salmon trout or salmon. 40 Examples The mixtures described in the examples below were processed in a twin-screw extruder (ZSK-30, Werner & Pfleiderer) at a product 45 throughput of 7 kg/h. The still-plastic extrudate is shaped to form granules by hot-cut pelletization.
5 The biologically active substance used in the examples below was a vitamin premix of the following composition: Vitamin A-500.000 IU/g 7.92 g 5 Vitamin E-500 mg/g 396.04 g Vitamin C 396.04 g Inositol 198.02 g Highly dispersed silicon dioxide 1.98 g 10 Example 1 A mixture comprising 14.15% by weight of a copolymer of 60% by weight N-vinylpyrrolidone and 40% by weight of vinyl acetate 15 having a K value of 30, 19.0% by weight of potato starch, 2% by weight of sodium hydrogen carbonate, 9.25% by weight of hydroxypropylmethylcellulose, 5% by weight of fish meal, 0.1% by weight of butylated hydroxytoluene (BHT) and 50.5% by weight of a vitamin premix was mixed and extruded. 20 Temperature of the barrel sections: 83, 92, 101, 100, 100, 105 0 C Temperature of the dye; 111 0 C The granules had a particle size of 3 mm *5 mm. 25 Sedimentation rate: 3.3 m/min Example 2 30 A mixture comprising 20.5% by weight of poly(vinyl acetate) having a K value of 63, 22% by weight of potato starch, 5% by weight of sodium hydrogen carbonate, 2% by weight of highly disperse silicon dioxide and 50.5% by weight of vitamin premix was mixed and extruded. 35 Temperature of the barrel section: 80, 100, 103, 101, 101, 105 0 C Temperature of the dye: 111 0 C The granules had a particle size of 3 mm * 5 mm. 40 Sedimentation rate: 3.5 m/min Example 3 45 A mixture comprising 5% by weight of poly(vinyl acetate), 39.2% by weight of potato starch, 2% by weight of sodium hydrogen carbonate, 3% by weight of highly disperse silicon dioxide, 0.1% 6 by weight of BHT, 50.5% by weight of vitamin premix and 0.2% by weight of a fruit flavor mixture based on strawberry and raspberry flavors was mixed and extruded. 5 Temperature of the barrel sections: 45, 80, 101, 101, 102, 1200C Temperature of the dye: 1300C The granules had a particle size of 3 mm * 5 mm. 10 Sedimentation rate: 3.1 m/min 15 20 25 30 35 40 45