Numerous problems are encountered in the feeding and medicating of fish. The behavior of fish at feeding is strongly influenced by prevailing conditions at the time of feeding. Such conditions include, for example, the temperature and acidity of the water; the level of dissolved nitrates and other substances in the water; the consistency and nature of the feed, e.g., hardness, taste and flotation properties; and the health state of the fish.
Known methods of fish medication include mixing medication, with fish feed. Oral administration of medicines in this manner is complicated by the tendency of most medicaments to adversely affect the taste of the feed, which becomes unacceptable to the fish. Moreover, many types of known medicated feeds are prepared in the form of pellets. Medication, and antibiotics in particular, are mixed into dry food pellets without considering the pharmaceutical aspects of drug formulation, and sold as medicated pellets for fish. The pellets are characterized by poor bioavailability of the drug substance. The pellets also sink too rapidly for ingestion by the fish. The unused portion of the medicated feed represents a source of pollution in the fish farming facility, or other environment in which the medicated feed is released.
Many fish medicines are toxic, in high concentrations. Thus, handling the feed coated with medication may be harmful to humans. Fish breeders utilizing "soft" medicated feed generally prepare the same by mixing the medication with available feed materials. Such non-industrial mixing methods fail to permit adequate control over the concentration of active material in the feed. The mixing of large quantities of biologically active materials poses a health hazard for the fish breeder. The dispersion of the medication in water, from disintegrated feed or carrier, represents an additional source of pollution or direct harm to the environment.
Several methods have been proposed to make fish feed more acceptable or more easily accessible to fish. U.S. Pat. No. 4,413,014 discloses a food or bait material comprising a solid edible porous corn material saturated with a fish attractant liquid. The article is produced with a core of feed solid material, and may also be coated with a solid edible material.
U.S. Pat. Nos. 4,393,087 and 2,358,320 disclose methods for rendering fish feed more available to fish by influencing the feed's flotation properties. The firstmentioned patent discloses a process for producing floating feed pellets formed from a combination of fish meal and a protein-containing material, including expanded grain particles to render the pellets buoyant in water. U.S. Pat. No. 2,358,320 describes a fish feed consisting of a material that is denser than water, but which is rendered buoyant in water by forming the material into hollow pellets.
International Patent Application No. WO 85/05015 describes a method of rendering feed more attractive to fish. Pellets having a soft consistency are formed with a surface coating of a hardenable gel material, such as, alginate, guar gum, tragacanth gum, pectin or gelatin. The pellets may be imparted with varying flotation properties.
While the above-described references are interesting, they do not disclose dosage forms containing medicines; nor do any of the references address the problems which may arise in the oral administration of medicaments to fish.
"Oxytetracycline Vet. EWOS IOG/KG Medicine Pellet for Fish 9P", manufactured by EWOS AB, Sodertalje, Sweden, (hereinafter "Product A") is prepared by mixing medication into fish feed according to pressure-pelleting techniques, followed by drying. Medicated feeds prepared according to such techniques are not buoyant, but rather sink rapidly, reducing the change of uptake by fish, and increasing the pollution of the environment. Furthermore, such feeds offer little control over the quantity of medicament actually assimilated by the fish, and suffer from poor absorption and bioavailability of the medicament.
"Skretting Tess Medicine Pellet for Fish (7.5g OTC/Kg)", manufactured by T. Skretting A/S, Stavanger, Norway, (hereinafter "Product B") is produced by applying a coating of medication to the surface of dry fish food. The medication is suspended in oil and sprayed onto the surface of the feed. The larger part of the medication remains on the surface of the feed pellet, while the balance is absorbed into the feed, together with the oil. Medicated feeds prepared in this manner suffer from being unpalatable to fish by virtue of the taste or smell of the medication deposited on the feed surface. The degree of utilization by the fish is particularly poor where the medication has a characteristic or penetrating taste, as in the sulfonamides or nifurazolidone, for example. Since the medication is present mainly on the surface of the feed, the fish breeder or worker will be exposed thereto. Moreover, the accuracy of the dosing is inherently poor in such feeds.
It is thus an object of the present invention to provide a dosage form for medicating fish, which eliminates the above mentioned disadvantages, while at the same time permitting effective delivery of medication to fish.