The production of fish feed is today carried out in the way that, by preheating and pressing or extrusion, a product is heated for formation of pellets having a diameter of about 11 mm. The size of the pellets is restricted by the possibility to keep each of them in one piece before their collapse, and by their ability to absorb oil. Heating of protein, especially with a low water content, may cause a reduction of the breakdown of the feed in the intestinal system of the fish and for that reason results in reduced feed conversion and fish growth.

Fishes of the type salmon, cod, coalfish etc do however, when in their natural environment, habitually eat food particles bigger than 11 mm. For that reason the product is manufactured as total composition pellets and those are then heated in oil for a few seconds, like frying, the oil addition constituting the last step. In both those systems the ability of the fishes, in an efficient manner to absorb the proteins which can be broken down, is small.

A better conversion of the feed is obtained if it is given to the fishes without having undergone a prior heating, i. e. the fishes are fed with proteins which have not coagulated. For that reason, during an early period, the fishes were fed with fish feed in a wet state. This did however result in significant difficulties since in wintertime the wet feed froze before it had reached the basins. It turned rancid. The result was massive feed spill deposits on the bottom below the fish raising space.

Also, the number of staff required was high. Due to those disadvantages one switched over to preproduced feed of the type mentioned above.

The object of the present invention is to solve the problem mentioned above by providing a method for manufacturing, from new raw substances, a feed to be used in fish farming, resulting in a minimized feed consumption thanks to an improved utilization of the feed. This is achieved thanks to reduced feed waste, and increased breaking down ability yielding improved feed absorption caused by an improved enzyme process, resulting from the fact that the proteins are not heated. The negative environmental effects are also minimized. The features characterizing the invention are set out in the subsequent claims.

Thanks to the invention there has now been provided a new method for manufacturing a feed which is to be used in fish farming and which is based on new raw substances. It does in an excellent manner satisfy its purposes and it can also be carried out in a simple, low-cost way. The teaching is that use is made of new raw substances which are freezed immediately before the feed is to be supplied to the farmed fishes. When e. g. mackerel, herring, hake, cod or the like is used there will remain rest products such as stomach, head and bones. Those products are milled and dehydrated in vacuum and, in some cases, fish oil may be added as determined by the pumpability and the stabilization properties. The durability can also be stabilized via the pH- value. When the raw substances arrive to the farm they are stored in, preferably cooled, tanks.

In connection with the feeding of the fishes the protein mass received is pumped into a mixer and one can then also supply

additives such as vitamins, mineral substances etc. The mass is then supplied to a freezing or cooling nozzle like a so-called "noodle string"whereupon it is compressed, its cavity then housing either air or fish oil. In this way it is possible to produce a floating product as distinct from the state of art feed which sinks in water and. is supplied from above.

The product provided according to the invention is, in the shape of a stream, supplied under the water surface so that it will rise to the surface. After a certain time the frozen product will thaw and then again sink, down to the bottom. In this way the fishes are offered two eating opportunities ; the first one during the feed passage up to the surface'and the second on during the return passage when the feed has become saturated at the surface and the air pocket dissolved. This mode of operation means that bigger feed particles can be used, that fight for food occurs more seldom and that the waste will be reduced.

Further, when the farming concerns flat-fishes, which have their eyes on the top side, it is important that the feed floats above the fishes. In that case the feeding is made from above in shallow basins.

Another advantage of the invention is that this system also offers a possibility to cover the lower portion of fish farms in the sea, so-called sea string-bags. In plants on the ground it becomes possible to reduce their depth. This also opens the possibility to use the feed supply pump system also for removal of manure from the lower portion if desired.

The invention will now be described with reference to a preferred, exemplifying embodiment.

The preferred exemplifying embodiment of the invention discloses a method for producing, from new raw substances, fish feed to be used in fish farming. The first step of the production process is to mill and dehydrate the starting fish feed to a protein mass which does then, in a second step, following a possible storing, exit through a freezing or cooling nozzle. Inside the nozzle the mass is formed to the shape of a nozzle string which is compressed from the outside with either air or fish oil in the cavity formed inside the string which is simultaneously frozen either inside or shortly downstream the nozzle. In connection with its delivery to the fishes the protein mass is pumped into a mixer upstream of the nozzle where it may be suitable, if so desired, to supply additives such as vitamins, mineral substances etc.

This fish feed production method according to the invention yields a floating product. The state of the art feed consists of sinking products which are supplied from above, in contrast to the invention where the feed is instead supplied from below in a stream entering below the fishes and then rising. After a certain time the frozen product starts thawing causing it to sink.