Feeding method and production technology of a vegetarian feed for carnivorous fish prepared from Spirulina and Chlorella algae that are produced by cell proliferation in production tanks in electrolyzed water with chlorine-neutralizing sodium thiosulfate and are subsequently dried, pelleted and packaged. The fish feed can be employed without the fish having diarrhea. As a result, the water in fish breeding tanks does not become immoderately eutrophic and at the same time the daily weight gain of the fish is not affected. An optimum daily growth rate and a fish flesh quality can be achieved without the use of animal and fish-based proteins in the fish food ration. The fish food is also inexpensive and ecologically sustainable and ethically acceptable, since it contributes to the rescue of the remaining fish stocks in waters worldwide.