Location: Cool and Cold Water Aquaculture Research
2020 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
Over the course of the five-year project #8082-31320-002-00D 2014-present period, significant progress was made on the two main objectives and their respective subobjectives which aligned with Components 3 & 4 of the 2015-2019 NP 106 Aquaculture Action Plan: 3. Health of Aquatic Animals, and 4. Sustainable Production Systems.
Progress towards Objective 1: Developing technically advanced, environmentally compatible, and sustainable closed production systems and techniques, included comparative economic and environmental analyses of land-based versus net pen Atlantic salmon production. The Conservation Fund Freshwater Institute (TCFFI) scientists used performance data from Atlantic salmon growout trials in conjunction with engineering design experience for planning and comparing land-based RAS to ocean net pen systems. Working with scientists at SINTEF (Trondheim, Norway), an analysis of the economics and environmental impact of land-based versus net pen production of Atlantic salmon was completed. Analysis indicates that the annual operating cost, for the modeled scale of 3,300 metric tonnes annual production, is approximately equal for land-based production and net pen production at $4.37 per kg of head-on gutted product; however, the capital cost of the land-based model system is approximately $54,000,000 compared to approximately $30,000,000 for the net pen system. Analysis of the environmental impact of the two production methods using life cycle assessment indicated that land-based salmon produced close to a U.S. market that uses an average U.S. electricity mix would have a much lower carbon footprint than fresh salmon produced in Norway in net pen systems that are shipped to the same market by airfreight. However, when land-based production is sited where electricity is provided by hydropower, the carbon footprint of the two production methods are approximately equal when transportation is ignored.
TCFFI scientists continued efforts to break barriers to scale-up of land-based closed-containment aquaculture. Although production of Atlantic salmon in land-based RAS offers an environmentally sustainable approach to meeting domestic demands for seafood, harvest strategies must be developed that ensure the product quality that consumers expect. TCFFI scientists determined that concerns about off-flavor in 4 kg Atlantic salmon can be mitigated by pre-disinfecting tank systems with hydrogen peroxide and using systems that do not contain hard-to-clean locations, such as aeration media, during the final 6-10 days of fish rearing; compounds associated with off-flavor were consistently reduced to levels which are below human tasting limits. Following these standard operating practices will maximize product quality for Atlantic salmon and other species that have been cultured in water recirculating systems.
To improve the environmental sustainability of land-based RAS production systems, TCFFI scientists evaluated the use of woodchip bioreactors for the removal of nutrients and suspended solids from fish farm effluents. As with all intensive agricultural systems, fish farms produce waste that has the potential to impact the surrounding environment. Certain aquatic environments, such as Chesapeake Bay and the Mississippi River basin, have become significantly impacted by the agricultural release of nutrients and other effluent components into their ecosystems. Woodchip bioreactors are trenches containing woodchips which in turn fuel heterotrophic bacteria that remove nitrogen (N) and total suspended solids (TSS) from passing effluent. TCFFI researchers established that woodchip bioreactors can capture the NO3-N and TSS (7.2 – 32.6 and 3.2 – 101 g per m3 of woodchips per day, respectively) from aquaculture effluent streams to minimize nutrient discharge into surrounding waterways. Our researchers also completed a cost and engineering assessment of a full, commercial-scale woodchip bioreactor to assist aquaculture producers with implementation of this technology. Based on these findings, the woodchip bioreactor is currently being recommended to fish farmers as a relatively low cost, low maintenance technology to treat aquaculture effluent and reduce environmental impacts and wastewater treatment costs.
Progress towards Objective 2: Improving salmonid performance, health and well-being in land-based systems through research on nutrition, rearing environment, and control of pathogens and fin erosion, included establishing safe limits for environmental parameters in Atlantic salmon RAS. Determining optimal environmental parameters for raising Atlantic salmon in freshwater RAS is critical to supporting the growth of land-based salmon production in the US. TCFFI scientists have defined safe levels 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; however, an upper nitrate-nitrogen limit for Atlantic salmon in freshwater RAS has yet to be defined. TCFFI researchers also identified optimal levels of dissolved oxygen and carbon dioxide, and have 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 US producers in the nascent RAS Atlantic salmon industry to raise healthy, well-performing salmon.
TCFFI continued to assess Atlantic salmon being raised to market weight in land-based systems using sustainable diets. The use of alternative protein sources in fish feed continues to increase as concerns persist surrounding the sustainability and cost of using ocean-harvested fish as protein and oil for fish feed. Furthermore, commercial farms are beginning to use land-based systems that recirculate water and allow production of market-size Atlantic salmon adjacent to markets, with less disease, and without perceived negative impacts on the marine ecosystem. TCFFI research has shown that a novel fishmeal-free diet fed to Atlantic salmon in RAS resulted in greater waste production but provided equal salmon growth, feed conversion, and survival compared to a traditional fishmeal-based diet. The fishmeal-free diet did not use any capture fisheries ingredients that were directly purposed for production of aquafeeds, thus resulting in a “zero to one” wild fish in to farmed fish out ratio and indicating the fishmeal-free diet was highly sustainable. These findings were adapted to larger-scale salmon production, for which we provided the first evidence that Atlantic salmon can be effectively raised to market-size while consuming a sustainable diet in a commercially relevant land-based system. This research provides infrastructure requirements and rearing strategies that increase Atlantic salmon production efficiency yet alleviate environmental impacts and reliance upon capture fisheries.
TCFFI scientists gained an increased understanding of the microbial agents associated with bacterial gill disease in rainbow trout. Bacterial gill disease (BGD) is a common and often devastating disease affecting aquaculture worldwide; however, our understanding of the opportunistic bacteria associated with BGD is surprisingly incomplete. We instigated natural BGD without direct pathogen challenge in rainbow trout via environmental manipulation, and used 454 pyrosequencing to determine the bacteria on BGD-affected and unaffected individuals. We found that Flavobacterium branchiophilum, the putative sole agent of BGD, as well as F. succinicans, were associated with BGD-affected fish. These novel results will inform further research on the natural occurrence of BGD in fish farm settings, and will provide information for researchers seeking to develop more efficacious therapeutants and/or vaccines for BGD.
Growth and fillet quality in commercially available rainbow trout were assessed at TCFFI. Determining if commercially available rainbow trout exhibit variable growth performance and fillet quality in RAS is critical to identifying genetic lines that maximize profitability. In collaboration with ARS researchers, TCFFI scientists determined that there was considerable variation in growth performance between genetic lines of rainbow trout; the fastest growing line reached 3 kg while the slowest line lagged 30% behind. These findings indicate that farmers interested in maximizing product yield on either a fractional (percent yield) or absolute basis (total biomass) should familiarize themselves with the growth potential of available stocks before purchasing eggs or fish for their operations. In contrast, indices of fillet quality such as the nutrient profile, texture, and color did not differ among commercial genetic lines. Therefore, a farmer or processor who values optimal fillet quality above growth-related traits can be more flexible in their genetic stock selection. Researchers also defined changes in processing yields and indices of fillet quality at different harvest weights throughout the production cycle, providing valuable data that RAS producers can use to predict growth trajectories and fillet characteristics.
Accomplishments
1. Use of all-female triploid Atlantic salmon in land-based recirculation aquaculture systems (RAS) eliminates pre-harvest sexual maturation. The use of all-female Atlantic salmon in land-based aquaculture systems (RAS) increases production. The early rate of maturation in male salmon reduces growth performance and down-grades fillet quality. ARS extramurally-funded scientists in Shepherdstown, West Virginia, showed that female salmon grew well in RAS from 1 kg to less than 5 kg harvest weight and that the all-female salmon did not exhibit maturation at harvest. This study showed that rearing all-female Atlantic salmon is an effective approach for land-based Atlantic salmon producers to improve the economic viability of this industry greatly.
2. Quantification of biomass loss during purging and processing. Eliminating off-flavor from farmed fish. Fish reared in recirculation aquaculture systems (RAS) develop an off-flavor that can be eliminated by implementing a purging period before harvest. ARS-funded scientists in Shepherdstown, West Virginia, withheld feed for six to 14 days during the purge period, resulting in a weight loss of 2 to 10 percent weight, but removed the off-flavors. These findings provide RAS salmon producers with critical data regarding harvest yield predictions, thus contributing to economic stability by increasing the accuracy of biomass production models.
Review Publications
Lepine, C.A., Christianson, L., Mcisaac, G., Summerfelt, S. 2019. Denitrifying bioreactor inflow manifold design influences treatment of aquacultural wastewater. Aquacultural Engineering. 88:102036. https://doi.org/10.1016/j.aquaeng.2019.102036.
Good, C., Davidson, J., Straus, D.L., Harper, S.B., Marancik, D., Welch, T.J., Peterson, B.C., Pedersen, L., Lepine, C., Redman, N., Meinelt, T., Liu, D., Summerfelt, S. 2020. Assessing peracetic acid for controlling post-vaccination Saprolegnia spp.-associated mortality in juvenile Atlantic salmon Salmo salar in freshwater recirculation aquaculture systems. Aquaculture Research. 00:1-4. https://doi.org/10.1111/are.14567.
