Location: Aquatic Animal Health Research
2024 Annual Report
Objectives
1. Develop, evaluate, and improve fish production systems for aquaponics.
Component 6: Problem Statement 6A
2. Develop, evaluate, and improve plant production systems for aquaponics.
Component 6: Problem Statement 6B
3. Develope environmentally and economically sustainable aquaponic systems.
Component 6: Problem Statement 6C
Approach
Auburn University faculty and their associated research team and ARS investigators will work collaboratively on both the aquatic animal and plant components in an effort to improve the yield and efficiencies of aquaponics production systems. Topics of interest to be explored include the optimization of: aquaculture system type, fish feeds, stocking densities, alternative aquatic species (e.g., high-value species such as pompano, red drum, cobia, marine shrimp, etc.), oxygenation strategies, animal and plant disease management, plant yields, improving nutrient and water use efficiencies, postharvest product quality, and salt tolerance.
Progress Report
Aquaponics integrates aquaculture (fish production) with hydroponics (growing plants in a soil-less environment) where waste produced by the fish can be utilized by the plants as nutrients. However, adding supplemental nutrients to enhance plant production is common. Frass, which is the manure of insects and the substrate used to culture them, can be used to enhance fish and plant production. Depending upon the culture substrate used to grow the insects, it may be possible to enhance both plant and fish growth with a dietary approach in an aquaponic system. ARS researchers in Stuttgart, Arkansas, in collaboration with researchers at the University of Arkansas at Pine Bluff (UAPB) and ARS researchers in Auburn, Alabama, evaluated channel catfish juveniles which were fed diets with, or without, 10% black solider fly larvae (BSFL) frass in an aquaponic system. Each aquaponic system had two different plant bed types, floating raft and media and were used to grow stevia and lavender. Channel catfish grew significantly better when fed a diet containing 10% BSFL frass compared to fish fed a diet that did not contain frass. Further, intestinal histomorphology showed reduced inflammation. The proximate composition of channel catfish was unaffected by diet, while both stevia and lavender had significantly more biomass when frass was added to the system, while plants grown in media beds were larger than plants grown in a floating raft subsystem. Frass significantly increased phosphorus in both stevia and lavender at week 8. Higher water calcium, magnesium, and nitrate levels may have allowed for higher growth rates as these nutrients are essential for proper plant health and growth. The significant increase of catfish growth was likely due to the upregulation of genes responsible for growth, mitigating intestinal inflammation, and significantly enhancing diet intake. Thus, it may be recommended that feeding catfish with BSFL frass and culturing stevia and lavender in media beds can substantially improve overall productivity.
There is a need for secondary schools to provide more authentic, hands-on experiences in science, technology, engineering, and mathematics (STEM) and, specifically, project-based investigation (PBI) environments in the classroom. This has been identified by the Next Generation Science Standards (NGSS) which informs teachers on useful teaching methods that could be utilized in the classroom. However, many high school students do not have a high value or understanding of science or the many disciplines that encompass the field of study. Thus, if secondary schools can teach scientific disciplines in a fun, hands-on, educational manner, this could improve student’s opinions of science and possibly get them interested in embarking on a career in the sciences. Aquaponics is a good candidate for hands-on classroom teaching since it involves many STEM disciplines, as well as ecology and environmental science. ARS researchers in Stuttgart, Arkansas, in collaboration with researchers at Kentucky State University, investigated how, and to what extent, a 10-week, hands-on aquaponics unit affected high school students’ understanding of standard-based ecological relationships and concepts concerning interactions in ecosystems and, specifically, the phenomena carrying capacity and bacterial nitrification process. Three different student groups who participated in the authentic, hands-on APBI curriculum (i.e., treatment groups) and a control group were given a pre- and post-content-aligned test which measured changes in students’ ecological knowledge. The results in this study revealed that the aquaponics curriculum was an effective method to provide meaningful learning and content understanding of standard-based ecological concepts and relationships. The evidence from this study suggests that authentic instructional experiences can facilitate students’ understanding of standard-based ecological concepts and knowledge of ecosystems, as the three treatment group students showed significantly higher mean difference (improvement) sum scores after taking the pre- and post-content-aligned assessment when compared to the control group. Overall, the gain in understanding can be attributed to the project-enhanced unit implemented in this study. The implications of this study suggest that hands-on aquaponics teaching curriculum can create learning environments that promote student learning of scientific concepts. In addition, hands-on projects can offer engaging curricula that can improve students’ interest in the sciences.
ARS Researchers in Auburn, Alabama, have planned, designed, and constructed a 2000-L freshwater, coupled, multi-tiered aquaponic demonstration system in which red swamp crayfish serve as the organismic nutrient source for a variety of vegetables and spice plants. As the water temperature is maintained at 27oC, numerous cool-temperature and warm-temperature plants were placed into the system to determine which species would be most appropriate for being grown aquaponically. Plants used in the system included: dill, Romaine lettuce, Bonnie spinach, kale, oregano, sweet basil, Thai basil, purple basil, rosemary, sage, sweet corn, Bush early girl tomatoes, red Husky tomatoes, green okra, ghost peppers, serrano peppers, and sea purslane. Suitable plants that were most appropriate to the conditions of the system are the three varieties of basil, sage, both varieties of tomatoes, green okra, rosemary, sea purslane, oregano, and serrano peppers. Concurrent with the design and construction of the freshwater aquaponic system, a 2000-L coupled brackish-water (11 ppt) aquaponic system was designed and constructed to grow halophytes and marine shrimp (pacific white shrimp). The halophyte presently being aquaponically grown is sea purslane; however, sea asparagus propagation and cultivation efforts are being planned and will also be grown in the system. Additionally, ARS researchers in Auburn, Alabama, are designing and constructing an outdoor, 4000-L coupled, freshwater aquaponic system with four 3-m plant trays.
Research collaborators at Auburn University have found that brackish wastewater from shrimp production is a good nutrient source for plants grown in an aquaponic system.
Research collaborators at Auburn University reported that optimal hydraulic retention time for aquaculture effluent in a nutrient film technique system used for lettuce production is six days. They found that longer times led to decreased yield due to the need to replenish plant nutrients, but shorter times did not increase yields.
Research collaborators at Auburn University reported that solution pH control is not necessary for cucumber production in a decoupled aquaponics system as long as potassium and iron supplementation are provided. This allows for less intensive maintenance and monitoring of pH in these systems, reducing monitoring and labor requirements.
Research collaborators at Auburn University stated that split-root systems can be used to improve salinity tolerance of kale for brackish water aquaponics; while split-root systems positively influence flavor and sensory profiles of tomatoes grown in brackish aquaponics and high-salinity hydroponics.
Accomplishments
1. Aquaponics allows for production of commercial densities of sweet potato slips. Aquaponics allows for production of commercial densities of sweet potato slips. Sweet potatoes are the sixth-most produced crop in the world and are increasingly being recognized as a 'super food' due to their high content of health-promoting carotenoids, vitamins, and minerals. The storage roots are grown in soil and while the roots can be used again as planting material, there is a point when this practice is no longer viable due to the accumulation of viruses and mutations that limit their production. In response, virus-indexed planting material, known as 'slips', are produced via apical meristem culture and are then vegetatively multiplied. These first-generation slips are often cultured in greenhouses to accelerate their growth and thus allow a longer growing season for their later storage root production. Sweet potato farmers rely on obtaining a sufficient amount of slips and thus, sweet potato slip production is itself an industry. Nevertheless, shortages are still common. Aquaponics integrates aquaculture (fish production) with hydroponics (growing plants in a soilless environment) where the wastes produced by fish are utilized by the plants as nutrients. Therefore, some of the potential benefits to aquaponics includes improved sustainability by reducing water usage/ discharge as well as enhancing food security as aquaponic systems can be operated in virtually any setting, including urban areas. In collaboration with researchers at the University of Arkansas at Pine Bluff, ARS researchers at Auburn, Alabama, conducted an 8-wk study where sweet potato slips were cultured at commercial densities in an aquaponic system which received weekly additions of insect wastes, in addition to nutrients supplied by the culture of Nile tilapia in the system. Water quality and sweet potato slip production/sugar/mineral contents were unaffected and were optimized in the aquaponic system.
2. Sunlight, and resulting algal growth, is not detrimental to plants grown aquaponically. Most previous aquaponic research has been conducted outdoors in tropical climates or within greenhouses in subtropical climates. However, the use of aquaponic technologies in more northerly latitudes or in urban areas will require greater environmental control and will likely be conducted in greenhouses or in insulated buildings with artificial lighting to supplement or replace natural light. However, in areas where natural sunlight could be used, the feeling was that algal growth resulting from the natural light, would be detrimental to plant growth as the algae would more rapidly absorb nutrients in the aquaponic system. Collaborators at Auburn University reported that illumination of fish tanks with natural sunlight improves fish growth performance compared to the conventional aquaponics practice of keeping fish in a dark/ shaded environment. Illumination results in algae growth that supplements fish feed for filter feeders, like tilapia. Until now, the presumption was that plant growth would be harmed by algal growth in the fish tank due to nutrient competition, but data indicate this not accurate. In one tomato trial, there was no effect caused by light source, while another experiment had significant increases in fruit production where the fish tank was exposed to natural sunlight.
3. Decoupled aquaponic systems may be more appropriate for growing larger fish. Decoupled aquaponic systems may be more appropriate for growing larger fish. The majority of aquaponic studies use small systems with small fish over short time durations. These data may fail to capture data reflecting the impact of fish size on plant performance. When using media bed substrate culture for tomato production, coupled operation of aquaponics is beneficial when fish were small. Coupled operation also led to higher nutrient status of plant tissues than decoupled operation, even after fish were larger. However, accumulation of sludge in the grow bed resulted in poor water drainage once fish had become larger (and produced more solids and nutrients). This led to root asphyxia and poor yields in tomatoes in coupled systems when fish were large. Collaborative researchers at Auburn University conducted a study which indicated that decoupled systems perform much better when fish are larger as the aquaponic system can utilize intermittent irrigation. This allows plant roots to have access to oxygen and avoid hypoxic conditions. Thus, it is recommended that aquaponic systems either use highly effective solids removal systems or switch to decoupled operation once fish become larger.
4. Pine bark makes for a readily-available substrate for cucumbers in an aquaponic system. Using aquaculture effluent (AE) to fertigate plants is gaining popularity worldwide. However, in substrate-based systems, the choice of substrate is essential due to their effects on crop productivity. Differences in the retention of nutrients by substrates makes it necessary to assess suitability for use in AE. Collaborative researchers at Auburn University conducted a study to evaluate greenhouse-grown Beit Alpha cucumber (Cucumis sativus L. ‘Socrates’) performance fertigated with AE in pine bark or perlite substrates, grown either as one plant or two plants per pot. A 2x2 factorial arrangement in a randomized complete block design with four replications for each season was used. The substrate effect on yield in depended on the density and season. The pooled yield over seasons showed pine bark had a significantly higher yield than perlite by 11% in one plant per pot, but lowered by the same amount in two plants per pot. In a second study, pine bark significantly reduced the leachate pH in both plant densities and reduced the leachate conductivity by 15% in two plants per pot. Foliar boron (B) was occasionally below sufficiency while manganese (Mn) was above sufficiency in pine bark due to its inherently low pH. Based on the data, it appears that the effect of substrates on cucumber yield fertigated with AE is dependent on the season and the number of plants per pot. Therefore, due to the local (Southern region of the United States) availability of pine bark, it could be a potential substitute for perlite, especially when using one plant per pot. In addition, pine bark could be used as an intermediate substrate to reduce the pH in AE for downstream use.
5. More frequent water exchanges and iron supplementation improves lettuce growth in a nutrient film aquaponic system. Nutrient film technique (NFT) is a popular, ergonomic, hydroponic system, but is not often used in commercial aquaponic systems due to lower efficiency in overall nutrient removal. Collaborative researchers at Auburn University conducted experiments to assess if NFT lettuce production could be improved by exchanging aquaculture effluent more frequently, and if so, determine the optimal water exchange rate. Aquaculture effluent (AE) was taken from a biofloc-based Nile tiapia production system. Treatments consisted of increasing hydraulic retention time (HRT/d): four-, eight-, twelve-, or sixteen-day water exchanges arranged in a randomized complete block design with five blocks. In one trial (Trial 1) where iron (Fe) was not supplemented, there was one replication. There were three replications for the second trial with iron supplementation. The analysis of lettuce plant size index and chlorophyll index (SPAD units) in Trial 1 were statistically different among the HRTs beginning 14 days after planting, exhibiting negative linear trends with increasing HRT; however, most foliar micronutrients were borderline sufficient, and all treatments showed foliar Fe deficiency. After iron supplementation (Trial 2), lettuce plant chlorophyll and size index exhibited quadratic trends with increasing HRT on 14 and 21 DAP, respectively. In Trial 2, plant fresh mass decreased linearly from 162.1 g/head to 147.1 g/head, with increasing HRT. Furthermore, iron supplementation eliminated Fe deficiencies in the plants albeit only up to 14 DAP. Our findings suggest that shorter hydraulic retention times provide a solution to using the NFT system in aquaponics especially with iron supplementation.
Review Publications
James, J., Dahl, S., Teichert-Coddington,, D., Kelly, A., Creel, J., Beck, B.H., Butts, I., Roy, L. 2024. Cohabitation of red swamp crayfish (Procambarus clarkii) and Pacific white shrimp (Litopenaeus vannamei) cultured in low salinity water. Aquaculture Reports. 36:102081. https://doi.org/10.1016/j.aqrep.2024.102081.
Romano, N., Webster, C.D., Datta, S.N., Pande, S.J., Fischer, H., Sinha, A., Huskey Jr, G., Rawles, S.D., Francis, S. 2023. Black soldier fly (Hermetia illucens) frass on sweet-potato (Ipomea batatas) slip production with aquaponics. Horticulturae. 9. Article 1088. https://doi.org/10.3390/horticulturae9101088.
Kalvakaalva, R., Prior, S.A., Smith, M., Runion, G.B., Ayipio, E., Blanchard, C., Wall, N., Wells, D., Hanson, T.R., Higgins, B.T. 2022. Direct greenhouse gas emissions from a commercial pilot-scale aquaponics system. Journal of the ASABE. 65(6):1211-1223. https://doi.org/10.13031/ja.15215.
Kalvakaalva, R., Smith, M., Ayipio, E., Blanchard, C., Prior, S.A., Runion, G.B., Wells, D., Blersch, D., Adhikari, S., Prasad, R., Hanson, T., Wall, N., Higgins, B.T. 2023. Mass-balance process model of a decoupled aquaponic system. Journal of the ASABE. 66(4):955-967. https://doi.org/10.13031/ja.15468.
Kalvakaalva, R., Smith, M., Prior, S.A., Runion, G.B., Ayipio, E., Blanchard, C., Wells, D., Blersch, D., Adhikari, S., Prasad, R., Hanson, T., Higgins, B.T. 2023. Life cycle assessment of a decoupled biofloc aquaponics facility across seasons. Journal of Cleaner Production. 429:139356. https://doi.org/10.1016/j.jclepro.2023.139356.