Environmental efficiency of recirculating water supply installations in the artificial breeding of noble crayfish

The aim of the study was to assess the effectiveness of a closed water-cycle technology that reduces the impact on natural water bodies and promotes the rational use of water resources. Experimental, analytical and statistical methods were used in the study: biometric measurements, hydrochemical monitoring, behavioural observations and correlation analysis. At the beginning of the experiment, the mean length of the juveniles was 1.2 cm and the weight 1.8 g, whereas by the end of the observations these indicators had increased to 5.1 cm and 11.7 g respectively. Survival remained within 85-100%, which indicated optimal cultivation conditions. The water temperature was stably maintained at 21-22°C, and the oxygen concentration fluctuated within 6.8-7.1 mg/l, ensuring normal metabolism of hydrobionts. Hydrochemical analysis showed the effective functioning of the biofilter: the concentration of ammonium nitrogen decreased from 0.35 to 0.07 mg/l, nitrites from 0.15 to 0.03 mg/l, and nitrates from 4.8 to 2.8 mg/l. Water transparency increased from 42 to 55 cm, and pH stabilised at 7.5, which indicated completion of the stage of biological stabilisation of the environment. Behavioural indicators also confirmed successful adaptation: activity of the juveniles increased from 2.1 to 4.6 points, the stress level decreased from 3.8 to 1.8 points, and cannibalism fell to 0.9%. After transfer to a natural water body, crayfish survival was 72%, the mean weight 133 g, and the proportion of females with eggs reached 65%, which confirmed the natural reproductive capacity. Economic calculations showed production profitability of 55.2% at a cost price of 138 UAH/kg and a net profit of 2050 UAH/m²/year. Energy consumption of the system was low – 3.6 kWh/day, saving of water resources – 92%, and the environmental effect – a 40% reduction in the catch of natural populations. The practical significance of this study lies in the possibility of using its results for the introduction of energy-efficient technologies for rearing noble crayfish on farms and in industrial enterprises in Ukraine