Aquaponics is an innovative growing method which combines two different types of growing techniques – aquaculture (farming of aquatic organisms) and hydroponics (cultivating plants). In the spring of 2016, lettuce (Lactuca sativa L. var. crispa, cultivar 'Kireve') was grown in the floating aquaponic system in which the aquaponic solution recirculated between aquaponic units containing African catfish (Clarias gariepinus) and hydroponic units with lettuce. Floating hydroponics was established as a control unit and was filled with standard hydroponic solution for the leafy vegetables production. The aim of this research was to compare morphological characteristics and mineral content of lettuce grown in both systems. Abiotic factors of the air in the greenhouse and of the nutrient solution in growing units were measured throughout the experiment. During the harvest, morphological characteristics of rosettes from both systems were measured and mineral analysis of the leaves was conducted. Lettuce grown in floating hydroponics had higher values of mass, diameter, height of rosettes, number of leaves and root length in comparison to lettuce from the aquaponics system. Also, the lettuce yield in the floating hydroponic (4.1 kg m-2) was significantly higher compared to floating aquaponics (1.7 kg m-2). Hydroponically grown lettuce had a higher content of nitrogen, phosphorus, potassium, iron and copper while lettuce from aquaponics contained more calcium, magnesium, manganese and zinc. Based on the results of this thesis, floating hydroponics is recommended for lettuce production but further research in terms of optimizing conditions of aquaponics production are needed for achieving better results.