2018 ASHS Annual Conference

Aquaponics is a new emerging agricultural production system that recycles residual nutrients resulted from fish waste for crop production. The culture environment in aquaponics is different from traditional farming, and a good aquaponics system should be designed to meet the growth requirements for fish, microbes, and plants production at the same time. Due to the excellent adaptability to a fluctuating water environment, tilapia (Oreochromis niloticus), a warm-water fish species, is the most popularly grown in commercial and scientific aquaponics systems in the U.S. The temperature environment of warm-water aquaponics system does not match with many vegetables popularly grown in aquaponic systems, most of which are cool-season crop species; however, there is no relevant information regarding this aspect. In order to compare the performance of crop species with different thermal requirements in warm-water aquaponics systems, two warm-season crops, cherry tomato (Solanum lycopersicum) and basil (Ocimum basilicum) and one cool-season crop lettuce (Lactuca sativa), were grown with tilapia for 2 months. Fish were fed once a day by 1% fish fresh weight. Water quality parameters were measured daily. The pH was adjusted by using a mixture of potassium hydroxide and calcium hydroxide (v:v=1:1) at around 7.0. Water was sampled for total ammonium nitrogen (TAN), nitrite, nitrate, and phosphate measurement every three days. At the beginning and harvest, crop growth parameters were measured. Bio-filter mediums were sampled for bacteria DNA extraction by qPCR with amoB as a molecular marker to check the population of ammonia-oxidizing bacteria (AOB) weekly during study period. Data showed that cherry tomato showed significantly higher SPAD than basil and lettuce, while both cherry tomato and basil showed significantly higher photosynthesis rate (Pn) values than lettuce. In addition, there was significant linear correlation between leaf temperature and net photosynthesis in cherry tomato and basil-based aquaponics systems, while no correlation was found in lettuce-based aquaponics systems between the two variables. Further, the results showed that higher leaf temperature increased net photosynthesis rate in cherry tomato and basil-based aquaponics systems, which may be partly explained by their higher thermal requirements. However, there was no significant difference in weekly AOB population density among the treatments, indicating that AOB did not play a critical role in plant growth variations. In summary, warm-season crops showed better growth performance in tilapia-based warm-water aquaponics systems.