Performance Evaluation of Hydroponic Grow-Outs in An Innovative Coldwater Aquaponic System Featuring Rainbow Trout and Lettuce

A 45-day trial was carried out to assess the production performance of different hydroponic media in a novel do-it-yourself (DIY) low-tech re-circulating aquaponic system for temperate regions with rainbow trout (Oncorhynchus mykiss) and lettuce (Lactuca sativa). Rainbow trout juveniles (average weight of 35.59 g) were stocked in the experimental units at 2.8 kg.m-3 and fed with commercial floating pelleted feed at 8 % of their body weight in three treatments and a control. The lettuce saplings were randomly planted in the river stone bed (T1), crushed stone bed (T2), raft/deep water culture (DWC) unit (T3) and control (C) soil bed (fortified with NPK fertiliser) with equivalent planting intervals of 42 saplings.m-2. The system, designed with low-tech simplicity, was managed without alkalinity correction and depended entirely on plant growth and metabolism for biofiltration. The water quality parameters such as temperature, pH, dissolved oxygen (DO), dissolved free CO2, hardness, total alkalinity, ammonium, nitrite, and nitrate varied significantly (P < 0.05) among the treatments compared to the control. The final individual weight, biomass gain, specific growth rate (SGR), and feed conversion ratio (FCR) of rainbow trout were significantly better (P < 0.05) in media beds (crushed stone and river stone) compared to control and DWC systems. The final mean weights of rainbow trout in river stone (12.33 ± 0.002 g and crushed stone (12.39 ± 0.054 g) treatments were significantly higher (P < 0.05) than in DWC (12.1 ± 0.023 g) and control (12.09 ± 0.002 g) treatments. The production of lettuce was significantly greater (P < 0.05) in all three treatments (river stone: 4.33 ± 0.123 g, crushed stone: 4.53 ± 0.09 g and DWC: 4.31 ± 0.163 g) compared to the control (3.31 ± 0.172 g). The DWC including the media bed systems facilitates the improved performance of lettuce saplings in terms of final height and leaf number. These results show that a low-tech media bed system without a supplementary biofiltration unit can achieve sustainable production of both fish and vegetables in temperate hilly terrains.