Location: Cool and Cold Water Aquaculture Research
2017 Annual Report
Objectives
Objective 1. Develop technically advanced, environmentally compatible, and sustainable closed production systems and techniques
Sub-objective 1.1 Optimize the cost and effectiveness of technologies to remove nitrogen and phosphorus from recirculating aquaculture systems and their effluent.
a) Optimize system water quality and evaluate salmonid performance when using membrane biological reactors to digest biosolids, remove nitrate, and practically eliminate water flushing requirements in each water recirculating system module.
b) Evaluate effectiveness of woodchip bioreactors for treating the effluent from water recirculating systems.
Sub-objective 1.2 Increase the energy efficiency of CO2 degassing technologies.
Sub-objective 1.3 Use refinements in water treatment process design and economies of scale to decrease the capital cost required per tonne of fish produced within water recirculating systems.
Objective 2: Improve salmonid performance, health and well-being in land-based systems through research on nutrition, rearing environment, and control of pathogens and fin erosion.
Sub-objective 2.1 Field-test rainbow trout germplasm resources when reared to 2kg harvest size within intensive water reuse systems and ID top performing individuals and families.
Sub-objective 2.2 Compare the effects of alternate protein (zero fish meal) versus fishmeal-based diets on growth performance and welfare of select families of Troutlodge rainbow trout when reared to 2 kg. We will also measure water quality, water treatment process performance, and waste production rates in recirculating aquaculture systems operated at low flushing rates.
Sub-objective 2.3 Identify strategies to minimize losses of Atlantic salmon smolt to Saprolegnia infections following vaccination in water recirculating systems.
Approach
The ability to provide U.S. consumers with high-quality, sustainably-produced seafood hinges upon research that supports increased domestic aquaculture production and the development of new and improved technologies. This proposed work encompasses several USDA ARS Action Plan components, primarily technology development for sustainable production systems (Component 4), alternative protein
investigation (Component 2), and disease prevention (Component 3). The first objective, which is focused on recirculating aquaculture system (WRAS) technology development, will investigate two water qualityimprovement technologies: (1) low-cost woodchip bioreactors for nitrate removal from aquaculture effluents, and (2) membrane biological reactors that produce a clean filtrate for reuse in the WRAS, which eliminates makeup water flushing and the point-source discharge. Refinement of water treatment processes and use of economies of scale to reduce capital costs of WRAS will also be a key focus. This
work will also investigate a new and potentially more energy efficient and cost-effective carbon dioxide stripping technology. Within the second overarching objective, we will evaluate the performance of commercially available rainbow trout strains (fingerling to 2 kg) cultured in WRAS, and will identify
strategies to minimize Saprolegnia infections in Atlantic salmon smolt cultured in WRAS after vaccinations. In addition, pressing societal concerns about the sustainability of fish feed and the rising cost of fish meal provide the emphasis to compare the effects of alternate protein (zero fish meal) and
fishmeal-based feed formulations on trout health and performance, waste production, and water quality. Through this work plan, we are eager to support the USDA in their forward-thinking efforts.
Progress Report
The overall goal of this project is to develop and improve technologies that enhance sustainability and reduce the environmental impacts of the modern U.S. fish farming industry. Progress was made within both specific research objectives that support this overall goal.
Objective 1 aims to develop technically advanced, environmentally compatible, and sustainable closed production systems and techniques. In response to increasing eutrophication from high nitrogen (N) and phosphorus (P) inputs, nutrient reduction goals have been established in areas including the Mississippi River basin and Chesapeake Bay watershed. Both point source aquaculture effluents and diffuse agronomy nutrient sources are suitable for innovative nutrient removal technologies. We evaluated the novel combination of denitrifying bioreactors, where carbon filled trenches consisting of woodchips fuel heterotrophic denitrification, and phosphorus filters where media remove dissolved P by adsorption and/or precipitation processes. Our findings demonstrated innovative compatibility and increased effectiveness when these two nutrient removal systems were combined. Effectively paired nutrient removal technologies will help meet established water quality goals in impaired watersheds.
High levels of suspended solids in aquaculture effluents create plugging and hydraulic problems in woodchip bioreactors operated over extended periods or at short hydraulic retention times. To extend the performance of woodchip bioreactors used to treat high-solids-content aquaculture wastewaters, an ongoing study evaluating an improved flow distribution system will determine treatment efficiency and deviation in hydraulic grade line due to plugging after long-term operation. We also assessed the ability of membrane biological reactors to produce a clean filtrate for reuse in the fish production system (sub-objective 1.1a). By digesting biosolids produced by the fish and removing nitrate, this technology eliminated makeup water flushing requirements and the point-source discharge, allowing more flexibility in locating and permitting fish farms.
Also in support of objective 1, cost and engineering assessments were completed to further characterize the feasibility and economics of specific technologies for recirculating aquaculture systems. We determined that denitrification woodchip bioreactors are a cost-effective and relatively low maintenance technology to remove nitrogen and suspended solids from fish farm effluents, thereby reducing environmental impact. In addition, we examined the cost of carbon dioxide stripping with a low lift aeration unit operated within a sump at several hydraulic retention times (sub-objective 1.2). This low-lift aeration technology reduced the fixed and variable costs for CO2 removal, because the process can be readily optimized according to demand and improves energy efficiency compared with more traditional cascade aeration columns. We also continued our engineering assessment of recirculating aqaculture systems (RAS) system design and scale to further improve the economics of land-based closed-containment systems for salmon production (sub-objective 1.3). We updated the biological planning for a facility to produce 3,000 tonnes per year of salmon using growth data from ongoing growth trials with all-female salmon. All-female strain salmon reduce the negative cost implications of early maturing male salmon in mixed sex groups by 5-10%. The updated bioplanning was used in the economies of scale analysis for designs that produce 500, 1,000, and 5,000 tonnes of salmon per year. The modular nature of RAS facility designs indicates limited economies of scale beyond 3,000 tonnes. These findings address several of the largest technology challenges facing domestic producers by providing new technology to reduce capital costs, improve energy efficiency, reduce water requirements, and increase nutrient removal at these farms.
The aim of Objective 2 is to identify culture practices to improve the performance of Atlantic salmon and rainbow trout produced in water recirculating systems. The intensity of water recirculation in these production systems produces a nutrient-rich environment with a diverse microbiome. As a basic requirement, the water treatment system must use nitrification to convert relatively toxic ammonia nitrogen into less toxic nitrate nitrogen. However, chronic nitrate limits have not been established for Atlantic salmon; therefore, we conducted a study to determine long-term chronic effects of two nitrate levels to post-smolt Atlantic salmon. Nitrate-nitrogen levels of 100 mg/L did not negatively affect Atlantic salmon growth, maturation, or health and were therefore deemed safe for Atlantic salmon culture under the conditions of this study. These criteria ultimately reduce production costs due to reduced water use, heat retention, and lower capital investment for nitrate removal. We also conducted a study assessing daily continuous, low-dose peracetic acid (PAA) administration as a strategy to replace ozone in water recirculating systems, through a comparison of water quality, fish health, performance, and welfare, and fillet off-flavor content. PAA was found to reduce accumulation of true color, but did not provide the dramatic improvements in water quality that can be achieved with continuous low-dose ozonation. Collectively, these studies better define water quality criteria requirements and treatment methods for salmonid health and welfare in closed or semi-closed systems.
Proliferation of iron bacteria and slime forming bacteria populations pose a significant threat to fish health and the operating efficiency of aquaculture systems, as accumulation of these bacterial biofilms can lead to biofouling and clogging of heat exchangers, aeration systems, chilling equipment, and other important aquaculture system components. We evaluated the effectiveness of ultraviolet irradiation for the treatment of iron bacteria and slime forming bacteria in aquaculture source water. Inactivation of iron bacteria by ultraviolet (UV) treatment was successful; however, the effect of UV on slime forming bacteria was inconclusive. This research provides the groundwork for a possible solution to the ubiquitous threat of iron bacteria biofouling in aquaculture systems. In addition, we studied a novel bacterial agent, Flectobacillus roseus, that demonstrated ability to colonize RAS to levels that where detrimental to fish health. F. roseus has only been identified recently in Asian aquaculture and has been responsible for the disease condition known as flectobacillosis. We cultured F. roseus from replicated RAS, and worked with ARS scientists to demonstrate that rainbow trout maintain high F. roseus-specific circulating antibodies following exposure to high waterborne bacterial counts. This collaboration is ongoing and will ultimately investigate the pathogenicity of F. roseus to rainbow trout without previous exposure to the bacteria. These findings demonstrate that a single bacterial species can dominate a RAS culture tank microbiome and that F. roseus could cause disease and mortality in such situations.
These studies are providing new technologies, tools, and information contributing to improved precision culture systems to meet current and future fish production needs of domestic fish farmers and diverse consumers, while minimizing the environmental footprint of production and enhancing fish welfare.
Accomplishments
1. Establishing safe limits for environmental parameters in Atlantic salmon RAS. Determining optimal environmental parameters for raising Atlantic salmon in water recirculation aquaculture systems (RAS) is critical to supporting the growth of land-based salmon production in the U.S. ARS extramural researchers in Shepherdstown, West Virginia defined the safe upper limit of nitrate-nitrogen, an end-product of biofiltration that accumulates as the level of water reuse increases, that Atlantic salmon can be exposed to without negative effects on growth performance, survival, or welfare indicators. Researchers also identified optimal levels of dissolved oxygen and carbon dioxide and described ideal swimming speeds that produce the best Atlantic salmon performance. Collectively, these findings defined acceptable ranges for parameters of water quality that are critical for U.S. producers in the nascent RAS Atlantic salmon industry to raise healthy, well-performing salmon.
Review Publications
Good, C., Davidson, J. 2016. A review of factors influencing maturation of atlantic salmon salmo salar with focus on water recirculation aquaculture system environments. Journal of the World Aquaculture Society. 47(5):605-632.
Cleveland, B.M., Leeds, T.D., Rexroad III, C.E., Summerfelt, S., Good, C., Davidson, J., May, T., Crouse, C., Wolters, W.R., Plemmons, B., Kenney, P. 2017. Genetic line by environment interaction on rainbow trout growth and processing traits. North American Journal of Aquaculture. 79:140-154. doi:10.1080/15222055.2016.1271846.
Christianson, L.E., Lepine, C., Sibrell, P.L., Penn, C.J., Summerfelt, S.T. 2017. Denitrifying woodchip bioreactor and phosphorus filter pairing to minimize pollution swapping. Water Research. 121:129-139.
Davidson, J., Summerfelt, R., Barrows, F., Gottsacker, B., Good, C., Fischer, G., Summerfelt, S. 2016. Walleye Sander vitreus performance, water quality, and waste production in replicated recirculation aquaculture systems when feeding a low phosphorus diet without fishmeal versus a traditional fishmeal-based diet. Aquacultural Engineering. 75:1-13.
Watten, B.J., Mudrak, V.A., Echevarria, C., Sibrell, P.L., Summerfelt, S.T., Boyd, C.E. 2017. Performance and application of a fluidized bed limestone reactor designed for control of alkalinity, hardness and pH at the Warm Springs Regional Fisheries Center. Aquacultural Engineering. 77:97-106.
