Investigation of the effects of liquid vermicompost use on system performance in aquaponic systems

This doctoral study was conducted in two phases with the aim of evaluating fish welfare in aquaponic systems and examining the effects of liquid vermicompost application on system performance under indoor conditions. Both experimental studies aimed to obtain comprehensive data sets by focusing on water quality, fish development, and plant performance in aquaponic systems established under different environmental conditions. The first experiment was carried out under greenhouse conditions, where fish and plant development were monitored over 180 days in an experimental setup established in a 4×5 m² area covered with UV resistant transparant greenhouse cover. Two systems were designed as the experimental group (DM) and control group (RAS), and 25 common carp (Cyprinus carpio) individuals were stocked in each system. At the beginning of the experiment, the fish had an average weight of 35.98±2.96 g in the RAS group and 36.06±3.23 g in the DM group, with stocking densities of 3.53±0.02 kg/m³ and 3.54±0.02 kg/m³, respectively. In the DM group, tomato (Lycopersicon esculentum) and lettuce (Lactuca sativa) seedlings were placed in the plant bed. Throughout the study, fish growth performance (length and weight increase, feed conversion ratio, survival rate), water quality parameters (NH₄⁺-N, NH₃-N, NO₂⁻-N, NO₃⁻-N, temperature, pH, oxygen, electrical conductivity, turbidity), and fish blood parameters (WBC, RBC, HGB, HCT, cortisol, Ca²⁺, Na⁺) were monitored. No statistically significant differences were observed between the groups in terms of fish development parameters (P>0.05). However, significant differences were found in feed consumption and stocking density between the groups (P<0.05). The second experiment was designed to investigate the effects of liquid vermicompost supplementation, aiming to compensate for plant nutrient deficiencies in aquaponic system water under indoor conditions. In a system consisting of nine experimental tanks, three groups were established: control (K), foliar application of nutrients (Y), and direct water application of nutrients (S). In each aquaponic system, 25 juvenile common carp (C. carpio) with an average weight of 22.82±7.97 g were stocked, along with a total of 11 plant seedlings 5 pepper, 2 lettuce, and 4 bean plants. Throughout the experiment, lighting with a constant intensity of 171.25 µmol/m²/s was provided to simulate daylight. The liquid vermicompost, which contains essential plant nutrients, was applied to the Y group by foliar spraying and to the S group by direct addition to the system water, both at a concentration of 1 ml/L. No vermicompost was added to the control group water. During the 90-day experimental period, water quality parameters were monitored daily (temperature, pH, oxygen) and every 15 days (conductivity, ammonia, nitrite, nitrate, phosphate, and turbidity). Findings showed that liquid vermicompost had no negative effects on fish behavior or water quality in either application method. Accordingly, it was concluded that the delivery of liquid vermicompost through the system water may be a favorable option to address basic plant nutrient deficiencies in aquaponic systems. As a result, it was observed that the presence of plants in the greenhouse aquaponic system did not have a measurable negative impact on water quality or fish development. In the second experiment, conducted under indoor conditions, the effect of foliar application of liquid vermicompost on plant development was found to be rather limited. Nevertheless, it was determined that the addition of liquid vermicompost at a concentration of 1 ml/L established after preliminary trials would not adversely affect fish welfare, while supporting plant development in terms of vegetative growth and fruit production.