CARP FISH REARING IN AUTOCHTHONOUS POLYCULTURE OF ONE AND THE SAME AGE (CYPRINUS CARPIO L., ARISTICHTHYS NOBILIS RICH. AND CTENOPHARYNGODON IDELLA VAL.)

For the needs of organic fish farming at the Institute of Fisheries and Aquaculture-Plovdiv, the levels of natural fish productivity of carp fish, bred in polyculture, based on a natural nutritive basis (an “autochthonous polyculture”) have been investigated. The experiment has been carried out in six fish ponds with a total area of 1.59 ha: three fish ponds – with organic manure applied (3000 kg.ha -1 of cattle manure), three fish ponds (no organic manure applied). Before flooding the ponds with water, 300 kg.ha -1 of quicklime has been applied, and during the vegetation period – an additional quantity of 150 kg.ha -1 . The quantity of the organic manure and quicklime used has been conformed with the requirements for organic fish farming. The polyculture structure has been the following: one-year old carp-500 pcs.ha -1 ; one-year old bighead carp - 300 pcs.ha -1 and one-year old grass carp-100 pcs.ha 1 , with an average single fish weight (ASFW) in the fish-stocking of ponds, respectively – 0.031; 0.021 and 0.038 kg. During the vegetation period the quality of water has been within the technological standards. The ponds have ensured a good natural nutritive basis. The organic manure applied has not contributed to fish productivity increase. From the experimental ponds max 720 kg.ha -1 of total yield and 693 kg.ha -1 of total gain have been obtained. The carp gain has reached up to 368 kg.ha -1 (final ASFW of 0.768 kg);of the bighead carp–345 kg.h -1 (final ASFW of 1.171 kg); of the grass carp – 118 kg.ha -1 (final ASFW of 1.300 kg).