Lyudmila Nikolova, Kostadin Dochin
An experiment on slaughter characteristics of bighead carp (Hypophthalmichtys nobilis Rich.) reared in polyculture of the same age, based on natural feeding in the ponds, was carried out at the Institute of Fisheries and Aquaculture – Plovdiv, Bulgaria. Some of the ponds (First Group) were not fertilized and others (Second Group) were supplemented with manure at the rates corresponding to the standards of organic production. The structure of polyculture was one and the same in all the ponds: K1 – one-year old common carp (Cyprinus carpio L.) – 500 pcs.ha-1 (half being scale carp and the other half – mirror carp); Tp1 – oneyear old bighead carp (Hypophthalmichtys nobilis Rich.) – 300 pcs.ha-1; Ð1 – one-year old grass carp (Ctenopharyngodon idella Val.) – 100 pcs.ha-1. The bighead carp reached a live weight of 0.766 kg under the experimental conditions, the fishes in the ponds fertilized with manure being about 13.6% heavier compared to fishes in the ponds of the other group. It was established that the slaughter yield and the relative share of the fillet in bighead carp were in average 54.3% and 35.4%, respectively, and, pond fertilization and the amount of phytoplankton did not have a statistically significant effect on fish development. The pond had a significant effect exerted through its area and by overgrowing with macrophytes. Infestation increase by up to 30% had a positive effect on the weight of the cleaned carcass, the fillet and the slaughter output.