674 Bulgarian Journal of Agricultural Science, 26 (No 3) 2020, 674–679 Use of Lemna minuta Kunth. for composition of sustainable diets and infuence on hydrochemical, technological and blood biochemical parameters in common carp (Cyprinus carpio L.) cultivated in aquaponics Katya Velichkova 1 , Ivaylo Sirakov 1 and Petya Veleva 2 1 Trakia University, Faculty of Agriculture, Department of Biology and Aquaculture, Students Campus, 6014 Stara Zagora, Bulgaria 2 Trakia University, Faculty of Agriculture, Department of Agricultural Engineering, Students Campus, 6014 Stara Zagora, Bulgaria * Corresponding author: genova@abv.bg Abstract Velichkova, K., Sirakov, I. & Veleva, P. (2020). Use of Lemna minuta Kunth. for composition of sustainable di- ets and infuence on hydrochemical, technological and blood biochemical parameters in common carp (Cyprinus carpio L.) cultivated in aquaponics recirculation systems. Bulg. J. Agric. Sci., 26 (3), 674–679 The purpose of this study was to investigate the infuence of aquaponically grown L. minuta used as a part of bioflter in recirculation aquaculture systems, with its subsequent inclusion in the composition (50 and 100% content of daily feed ratio) in sustainable diets on hydrochemical, biochemical blood and technological parameters in common carp (Cyprinus carpio L.) fngerlings cultivated in aquaponics recirculation systems.At the end of the experiment were calculated average fnal weight, specifc growth rates, feed conversion ratio, meat quality and blood biochemical parameters. The inclusion of up to 100% duckweed (L. minuta) in feed for common carp fngerlings decreases the quantity of ammonium, nitrite, nitrate and phosphate accordingly with 66%, 71.4%, 38.8% and 44.1%compared with the quantities of these parameters found for experimental groups fed with feed without inclusion of L. minuta. The carps fed with inclusion of up to 50% duckweed showed better growth of fsh, SGR and FCR compared with fsh fed with a diet without substitution of duckweed. Keywords: aquaponic recirculation system; blood parameters; carp; growth; Lemna minuta Introduction The usage of expensive and defcit components for the composition of feed for hydrobionts imposes the search of al- ternative components. This problem in the last years is of pri- mary importance for the aquaculture sector. The rapid devel- opment of aquaculture in the world leads to the bigger needs of fsh meal and its price rising (Hardy & Tacon, 2002). This has a detrimental efect on the populations of open-water fsh from which fshmeal is made. Increasingly sought appropriate and cheap raw materials to replace the fsh meal, but with good nutritional content.Many researchers investigated the usage of diferent plants with high nutritional value like beans (Azaza et al., 2009), soy (Deng et al., 2006), sunfower (Rinchard et al., 2002), cereals (Stoyanova & Delchev, 2014; Stoyanova & Kuneva, 2018), vegetables (Mundheim et al., 2004). The plants from genera Lemna probably could be the answer to the posed challenges from the aquaculture sector because they contain more than 50% protein (Sirakov & Velichkova, 2018). Duckweed is the smallest fowering plant in the world witch fast growing and easily adapt to various aquatic condition. Also, they used for water treatment and bioremediation (Velichkova & Sirakov, 2019). Duckweed was very efective in the removal of nutrients, soluble salts, organic matter, heavy metals and in