Effects of feed loading rate on growth of Bibb lettuce (Lactuca sativa) with nile tilapia (Oreochromis niloticus) in aquaponic systems

Fish feed is a highly variable recurring expense for aquaponic farmers. Financially viable aquaponic businesses require maximizing output while minimizing expenditures. Since fish feed is the primary nutrient input for both fish and plant growth, it is important that the “feed:plant ratio” is sufficient but also economical. The standard loading rate for most aquaponic systems is 60 g of feed/m 2 plant area/ day (g/m 2 /day). However, it is unclear if this loading rate is the most cost effective for this specific enterprise. This study compared a range of feed loading rates for aquaponic production of Bibb lettuce ( Lactuca sativa var. capitate). Utilizing six replicated aquaponics systems, six treatments were evaluated in terms of total biomass production of Bibb lettuce over three production cycles. Nile tilapia ( Oreochromis niloticus ) were fed a 32% protein feed at loading rates of 15, 30, 45, 60, 75, and 90 g/m 2 /day based on the growing area of the hydroponic unit (2.7 m 2 ). The 15 g/m 2 /day treatment had significantly less total biomass of plant production (4693.7 ± 397 g) than all other treatments, which did not differ from each other. Feed Conversion Ratio of plants (FCR plant ) and Plant to Fish Mass Ratio for experiment (PFRM exp ) were calculated and determined that treatments 30, 45, 60, and 75 were within the standard operating performance for protein and energy retention from feed. Treatments 15 and 90 fell outside of the standard performance likely due to low nutrient and micronutrient concentrations, suboptimal pH and temperatures, and/or buildup of mineral salts.