Aquaponics has received considerable attention in recent years as a bio-integrated model for sustainable food production. Tilapia and lettuce are the most commonly used combination among aquaponics producers, hobbyists and educators. Therefore, the goal of this literature review was to aggregate the knowledge on the current status of tilapia/ lettuce production, fish densities, systems configuration, common lettuce varieties, and identify research gaps. Among the forty reviewed publications, 72.5% were using Nile tilapia, 17.5% were using red, 2.5% were using red Mozambique, 5% were using rocky mountain strain and 5% of the articles stated that they used tilapia without reporting the species. Throughout the reviewed publications, tilapia initial density used ranged from 0.34 to 28.4 kg/m3, which depended on the purpose of the study, experimental size and design. Nile and red tilapia final yields were in the range of 12.58 to 28.50 and 9.81 to 50.45 kg/m3 , respectively. For the hydroponic unit, 55% of the publications used deep water culture (DWC), 35% used nutrient film technique (NFT), and only 10% used media bed (MB). Culture period was up to 8 months, but these long culture periods used staggered fish production. Harvest schedules were determined based on target lettuce size and experimental design (~4-5 weeks). Basil, cucumber and cherry tomato were used in aquaponic systems to optimize efficiency. Some of the gaps this review identified includes fish culture data (i.e., fish initial weight, density, duration, and/ or yield) , which were not completely presented in multiple articles. The optimum ratio between fish feeding rate and plant growing area (57 g of feed/day/m2) was originally calculated at the University of Virgin Island and published in 1988 using Bibb lettuce. This ratio has been used by farmers and researchers as a rule of thumb for years. However, this recommended ratio did not take into account other factors such as fish species, protein content of the diet, plant species/ variety, plant density, biological filtration, and air flow in the grow bed. Hence, the current review is suggesting that fish to plant ratio and fish density needs to be re-evaluated. As there is a thermal preference mismatch between tilapia and lettuce , there is a need to evaluate the optimum temperature for both to obtain the highest grow th performance. Nowadays, it is recognized that the genetic quality of farmed stocks must be routinely improved and protected. Therefore, feeding frequency, feeding amount and stocking densities in aquaponic systems should be continuously revaluated with the improved strains of tilapia as well as heat tolerant varieties of lettuce.
Keywords: fish density, lettuce varieties, fish feed, fish/ plant ratio, aquaponic system.