The use of fish waste to produce silage is a practical approach to decrease its discharge into the environment and obtain a liquid organic fertilizer (LOF) for aquaponics (AP) system. The aim of this study was to investigate the elemental composition of fish silage produced from rainbow trout (Oncorhynchus mykiss) waste using two species of lactic acid bacteria (LAB), including Lactobacillus casei and Lactobacillus plantarum and the impacts of adding the best biological fish silage (BFS) in terms of its elemental contents as a water additive on growth performance of Nile tilapia (Oreochromis niloticus) and basil (Ocimum basili- cum) plant in a coupled AP system. The results showed that that calcium, magnesium, phosphorus, iron, zinc, and manganese concentrations significantly increased during 21 days of microbial fermentation of fish waste in the control and the LAB groups (p<0:05). The concentrations of magnesium, iron, manganese, and zinc in the LAB groups were significantly higher than the control (p<0:05). Nile tilapia (O. niloticus) fish and basil (O. basilicum) plant were cultured in two AP systems without and with adding BFS obtained from rainbow trout waste using L. plantarum, referred to AP system (control) and AP-BFS, respectively. The results showed that the growth performance parameters of Nile tilapia fish, including the final weight, weight gain rate (WGR), average daily gain (ADG), specific growth rate (SGR), and food conversion ratio (FCR) improved in the AP-BFS system by 12.22%, 23.89%, 20%, 16.26%, and 19.86% compared to the AP group (p<0:05). The dry matter and crude protein contents of whole-body fish increased significantly in the AP-BFS system compared to the AP group (p<0:05). The morphological and biomass indices of basil plants, including total plant fresh weight, leaf, shoot and root fresh weight, shoot height, root length, and number of leaves, nodes, and buds per plant in the AP-BFS system were significantly higher than the AP group (p<0:05). The phosphorus, potassium, and iron contents of plant tissues were significantly higher in the AP-BFS than the AP system (p<0:05). Nitrate concentration was significantly lower in the AP-BFS system than the AP system (p<0:05). In conclusion, the use of LAB for production of fish silage improved nutrient recovery from rainbow trout waste. Adding BFS to the AP system improved the growth performance of Nile tilapia fish and basil plants.

Keywords