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[Extract] Aquaculture selective breeding programs employ a closed nucleus mating strategy whereby animals displaying sought-after characteristics are mated to produce next generation offspring with increased pre-valence of desirable phenotypes. Offspring exhibiting high genetic merit for favorable traits are then usually chosen as candidate parents for the subsequent breeding cycle. The selective breeding process is replicated each succeeding generation in order to accumulate genetic gain within the breeding population. The long term success of these closed breeding systems is dependent on a number of factors: including, the heritability of a trait, the intensity of selection, the additive genetic variance observed in the founding population, and the amount of additive genetic variance maintained over subsequent generations (Falconer et al., 1996; Loughnan et al., 2016). If breeding practices are not properly managed, the number of animals with high relatedness will increase (Gjedrem and Baranski, 2009b), leading to a substantial loss of genetic diversity over subsequent generations (Pante et al.,2001). The maintenance of genetic diversity is critical to accommodate current and future changes in production environments, and if left unchecked, it can lead to inbreeding through increased homozygosity and deleterious fitness consequences associated with inbreeding depression (Pante et al., 2001). This loss of genetic diversity can also hamper progress within the selective breeding program as it limits the amount of genetic variance available for selection (Falconer, 1960).

Our previous conclusions, that manures may be ineffective in raising aquaculture yields above levels attained by daily N and P fertilization, is limited to conditions of soil and water naturally rich in nutrient minerals and carbonates. Manures may be valuable inputs when soil and water are poor in essential nutrients, or of a low pH. Situations exist in which manures are the cheapest source of N and P minerals.

Aquaculture has experienced a burgeoning growth worldwide in the last decade resulting in nearly 50% of seafood originating from aquaculture farms. However, there are less studies on the utilization of the manure produced by aquatic organisms in comparison to warm-blooded livestock. Aquaponics offers more efficient utilization of nutrients and can reduce the operational costs in aquaculture. This paper presents the results of a study to identify the optimal settings to digest fish manure through a microbial-assisted aerobic bioprocess, using endogenous heterotrophic and nitrifying bacteria. The effects of pH (5.5, 6.0 and 6.5), temperature (30, 35 and 40 °C) and duration (1–30 days) on kinetics of nitrogen mineralization were investigated and compared to a control bioreactor (carried out without pH adjustment). The mineralization dynamics for all pH-controlled bioreactors revealed that only ammonification occurred. No nitrification was observed for all three-temperature conditions and throughout the entire bioprocessing period. The mineralization process in the control bioreactor, on the other hand, followed the typical non-inhibited nitrogen mineralization (i.e., release of ammonium followed by oxidation into nitrate). However, nitrate was only observed at temperatures

Geosmin (GSM) and 2-methylisoborneol (MIB) are secondary metabolites of cyanobacteria that are often present in recirculating aquaculture systems (RAS) and are problematic, even at low (ng L−1) concentrations, due to their taste and odor effects on water and accumulation in the lipid tissue of fish. Removal of these compounds is difficult due to their extremely low concentrations and advanced treatment technologies, such as advanced oxidation processes (AOPs) have to be employed. In this study, a novel AOP consisting of immobilized TiO2 in a UV reactor was tested at bench scale for removal of GSM and MIB in both batch and continuous flow modes. Batch reactor application at a full-scale RAS resulted in average GSM and MIB removal efficiencies of 61% and 72%, respectively, with a 6 h treatment time. No significant removal of GSM and MIB was observed in continuous flow mode, most likely due to both lower residence time and low initial concentrations of both compounds. No negative effects were observed on downstream biological wastewater treatment processes, indicating that the proposed UV-TiO2 process can be safely integrated into RAS.

In addition to environmental factors, particle size can interfere with the nitrification process because smaller flocs are less efficient in terms of ammonia and nitrite oxidation. The objective of the present study was to evaluate, in three experiments, the effect of the biofloc size on the nitrification process during the production of the white shrimp Litopenaeus vannamei in a BFT system. In all experiments, 1% of biofloc inoculum from production tanks was used. Water samples were taken to photograph and measure the flocs. Measurements of temperature, salinity, nitrogen compounds and total suspended solids were also carried out in the experiments. In experiment 1, the flocs were separated by sifting the water through mesh nets of 50, 150 and 300 μm in size. In addition, there was a control treatment with integral flocs. In experiment 2, the bioflocs were separated into 300 and 600 μm size classes and were compared with an integral control. Experiment 3 aimed to evaluate the nitrification process in treatments with flocs smaller than 150 μm, in flocs without handling (Control), and in the treatment where flocs were partially filtered in a 50 μm mesh for five days. This treatment resulted in a reduction in the particle size; however, when the meshes were later removed, and the biofloc size increased again. Different from our original hypothesis, the results of these three experiments indicate that the size of the biofloc, as well as the amount of total suspended solids, do not affect the nitrification process in the BFT system. However, all treatments that included manipulation through sifting showed a delay or a decrease in the nitrification activity. Thus, it is likely that, more than the particle size or floc abundance, the rupture of the floc structure affects the distribution and interaction of nitrifying bacteria with reflections in the nitrification process.

Reducing dependency on environmentally unsustainable formulated feeds, most of which include limited reserves of fishmeal as a protein source, is a priority for the aquaculture industry, particularly for intensive culture systems. One approach is to increase nitrogen reuse within the system by feeding nitrogen-rich aquaculture effluent to deposit feeders, thereby closing the aquaculture nitrogen-loop. This study, for the first time and on a laboratory-scale, has reared juveniles of the sea cucumber Holothuria scabra at high densities solely on particulate organic waste from a commercial-scale land-based abalone recirculating aquaculture system. Furthermore, growth rates and biomass yields were increased significantly by adjusting the effluent C:N from 5:1 to 20:1 by adding exogenous organic carbon sources (glucose, starch and cellulose), so fuelling accelerated heterotrophic bacterial production within the redox-stratified tank sediment. Sea cucumber juveniles reared solely on effluent had a biomass density of 711 g m−2 after four months whereas animals reared on starch-amended effluent (the best performing treatment) had a final density of 1011 g m−2. Further optimisation of this approach could increase biomass yields and pave the way for the commercial cultivation of deposit feeding animals on waste streams, thus contributing to more environmentally sustainable aquaculture. Here, the nitrogen that originated from fishmeal is not lost through the discharge of aquaculture effluent; rather, it is immobilised into single cell biomass that is up-cycled into high-value secondary biomass. We demonstrate that sea cucumbers can be produced at high density through the manipulation of the C:N ratio of aquaculture effluent.

Reverse electrodialysis (RED), based on non-precious electrodes, was applied to disinfect domestic aquaculture wastewater. It was found that treatment could be achieved either by an anodic reaction of electro-generated sodium hypochlorite (NaClO) or via a cathodic reaction of electro-generated hydrogen peroxide (H2O2). Without circulation, the disinfection rate was sub-optimal and depended on the anodic and cathodic reactions, reaching 82 ± 5% at the anode (0.3–2.9 mg/L of chlorineDPD, pH 3.2 ± 0.4) and 59 ± 7% at the cathode (2.9–8.7 mg/L of H2O2, pH 10.7 ± 0.3). In contrast, a high removal efficiency of ≥99 ± 1% was obtained when anodic and cathodic solutions were circulated due to the synergetic effect between HClO and H2O2 (0.1–2.1 mg/L of chlorineDPD, 3.9–4.9 mg/L of H2O2, pH 7.8 ± 0.2). Both operating modes resulted in a stable power production of 6 ± 0.5 W/m2. These results support the view that RED can offer a cost-effective and energy-efficient option for disinfecting aquaculture wastewater.

Maintaining low concentrations of nitrogen compounds in aquaculture water is a key requirement for a recirculating aquaculture system (RAS), due to the potential detrimental effects of ammonia or nitrate on fish growth and metabolic activities. Herein, a microbial fuel cell (MFC) was investigated to accomplish the removal of either nitrate or ammonia from real RAS water (with simulated daily nitrate/ammonium accumulation) while generating electricity, via aerobic nitrification in the cathode, electricity/concentration driven transport across anion exchange membrane, and subsequent heterotrophic denitrification in the anode chamber. The experiment went through two stages, nitrate removal (Stage I) and ammonia removal (Stage II). In Stage I when daily nitrate addition was performed to mimic nitrate accumulation (0.050 kg NO3−-N m−3 NCC d−1, NCC: net cathodic chamber volume) in the MFC cathode, a stable current density of 12.48 A m−3 could be achieved with a 73.3% nitrate removal and 91.3% COD removal at the end of day 15. To better mimic ammonium accumulation in the RAS effluent without a biofilter, daily ammonium addition (0.050 kg NH4+-N m−3 NCC d−1) was performed in the cathode in Stage II. The MFC system achieved a total inorganic nitrogen removal rate of 0.051 kg N m−3 NCC d−1, and a COD removal efficiency of 91.8% with a current density of 74.00 A m−3. A preliminary analysis of energy balance indicated that the proposed MFC could potentially achieve energy-positive RAS water treatment with a net energy production of 7.50 × 10−3 kWh m−3 treated RAS water or 0.145 ± 0.031 kWh kg−1 removed nitrogen. The results of this study indicate that MFCs have a potential to treat RAS water with simultaneous energy recovery.

International audience; Constructed wetlands (CWs) are environmentally-friendly methods for mariculture wastewater purification. The hydraulic regime is a key factor in the effectiveness of sub-surface flow CW treatment. The objectives of this study were to investigate the effects of five hydraulic operating regimes (i.e. Intermittent, Continuous, Batch I, Batch II and Batch III) on the purification performance of CW treated with mariculture wastewater and to assess the correlations between enzyme activities (i.e. urease, dehydrogenase) and purification performance of CW. Fifteen pilot sub-surface CWs with Salicornia bigelovii were investigated for the performance of CW as well as urease activity (UA) and dehydrogenase activity (DA). Over the experiment, removal efficiencies of TAN, NO3−-N, TN and COD under five hydraulic operating regimes were 26.6 to 37.2%, −6.0 to 16.5%, 9.4 to 16.8% and 33.9 to 44.6% respectively, corresponding to removal rates of 147.6 to 456.9 mg m−2 d−1, −18.1 to 229.2 mg m−2 d−1, 174.0 to 603.6 mg m−2 d−1 and 501.9 to 1421.6 mg m−2 d−1 respectively. CW with a Batch III operating regime had the best treatment performance, with mean removal efficiencies of TAN, NO3−-N, TN and COD of 37.2%, 16.5%, 14.9% and 34.0% respectively, with the corresponding removal rates of 456.9, 229.2, 603.6 and 873.6 mg m−2 d−1. As for enzyme activities, the UA was significantly higher in CW under Batch II than in Intermittent and Continuous operating regimes and the DA in CW with Batch I was significantly higher than under an Intermittent operating regime. UA and DA had significant positive correlations with COD concentrations but negative correlations with TAN and TN concentrations. The correlation analysis results showed that UA and DA can be an important indicator in evaluating removal performance of CW with Salicornia bigelovii in marine aquaculture wastewater treatment.

Fermented soy pulp (FSP) is currently capturing attention worldwide because of the high price of fish meal and its inconsistent supply in recent years. FSP replaces fish meal as a source of protein and energy towards improved fish health and growth. The protein replacement was employed in this study to assess the growth and health status, digestive enzyme, amino acid profile, and immune-related gene expression of African catfish, Clarias gariepinus. The duration of the feeding experiment was 70 days. Five isonitrogenous. (32% crude protein) diets were prepared with FSP replacing D1 (0% FSP), D2 (25% FSP), D3 (50% FSP), D4 (75% FSP) and D5 (100% FSP) to FM component of the diets. D1 diet with 0% FSP was considered as a control. The fermentation process of FSP was carried out for three weeks. This resulted in the experimental diets having significantly different (p

Population growth increases wastewater production, enhances environmental concerns, and increases wastewater treatment costs. This study aimed to use Anodonta cygnea (freshwater mussels) exposed to some water pollution in a closed cycle to treat wastewater by consuming harmful or undesirable pollutants in water. The results demonstrated that mussels eliminated all microalgae, reduced organic pollutant concentration (chemical oxygen demand removal rate 40% faster than lacked mussels tank), and removed some water hardening minerals such as Calcium (Ca) (more than 77%) and Nickel (Ni) as heavy metal (more than 78%), confirming that freshwater mussels could be helpful in the wastewater treatment cycle. The method can be used as the practical implementation of setting up a semi-natural system for the decentralized wastewater purification relying on the recruitment of mussels. The method also suggests a favorable and eco-friendly treatment mechanism to remove chemical oxygen demand, chemical elements, biological pollutions, and microorganisms.

Biofouling causes major functional and economic problems for aquaculture due to their settlement and subsequent growth on fish-cage netting. As biofouling management is an economic and environmental issue, feasible management practices are clearly required to balance industries and environmental requirements. The most frequent way to control biofouling in aquaculture is by applying Cu-based antifouling paints on fish nets to prevent the undesired growth of biofouling. The most important fish species employed in marine fish farming are cultivated with knotted nylon and ultra-high-molecular-weight polyethylene (UW-polyethylene) nettings. In this study, we examined the effects of two commercial Cu coatings and two manufactured net materials (nylon and UW-polyethylene) on biofouling biomass, community structure, Cu bioaccumulation and the metal composition of fouling assemblages in order to provide farmers with a tool to help reduce the environmental impact of the biocide employed for coating nets. The MDS ordination of the samples coated with both paints on nylon and UW-polyethylene nets showed a gradual modification of community structure associated with rising Cu concentrations. The PCA analysis indicated that the ordination of trace element composition of biofouling varied between concentrations and nets in both paints. The experiments revealed that the fouling biomass decreased following negative exponential regression with an increasing Cu concentration. The increase in fouling biomass with reduced Cu bioaccumulation was greater in nylon than in UW-polyethylene nets. In the nylon nets, the median bioaccumulation on nets (CuF-50) rose with an 0.75- to 0.82-fold increase in the basal biomass. Conversely, biomass increased 0.50- to 0.63-fold the basal or minimum fouling biomass with a full antifouling paint concentration (B0) when CuF-50was calculated in the UW-polyethylene nets. These results suggest that similar reductions in bioaccumulated Cu in both nets could be achieved without sacrificing excessive fouling biomass increases.

Minimizing ammonium is one of the most important concerns in the practice of aquaculture. Chemoautotrophic bacterial nitrification (CBN) and heterotrophic bacterial assimilation (HBA) are the two main ammonium pathways in aquaculture water under light-limited conditions. CBN oxidizes ammonia–nitrogen (NH4+-N) to nitrite–nitrogen (NO2−-N) and finally to nitrate–nitrogen (NO3−-N), and this is the primary strategy employed in recirculating aquaculture systems using fixed-cell bioreactors. Zero-exchange management systems based on HBA and biofloc technology have been developed referred as biofloc aquaculture systems. HBA is encouraged in biofloc aquaculture systems by increasing the C/N ratio. However, NO3−-N build-up was found in many studies examining these systems, with CBN proposed as the responsible mechanism and documenting the factors leading to the occurrence of the CBN process. This paper examines the relative importance of CBN and HBA in biofloc aquaculture systems. A mechanism is proposed and future study aimed at mediating NH4+-N pathways in biofloc aquaculture systems is recommended.

Intensive pond cultivation of Gracilaria may achieve maximal yields by enrichment of seawater with ammonia and CO 2 . In the present study, we examined the use of organic waste material as a source of ammonia and inorganic carbon. A biofiltration system was constructed, consisting of several fermentation tanks and a fluidized bed reactor for the required bioconversion of organic wastes. Gracilaria conferta was cultured in a 30 m 2 pond from which seawater was circulated through the biofiltration system for a period of nine months. As compared to the filtered seawater used for water supply, the outlets of the fermentation tanks and the fluidized bed reactor showed significant increases in dissolved inorganic carbon and ammonia concentrations and significant decreases in oxygen concentrations and redox potentials. The most efficient organic waste compound tested had the highest C/N ratio. No significant differences were found between the Gracilaria yields of the control and biofiltration pond systems. These results might contribute a fundamental improvement in the economy of Gracilaria pond cultivation by water recycling through such a biofiltration system. Statement of relevance The system might contribute a fundamental improvement in the economy of Gracilaria pond cultivation.

Hydraulic retention time (HRT) is one of the most critical operational parameters for solid-phase denitrification. The effect of HRT on solid-phase denitrification reactors (DR) packed with corrugated paperboard was investigated in recirculating aquaculture systems (RAS). Denitrification efficiencies of DR were 81.21–85.05% at HRTs of 0.5–2.0 h. The optimal HRT for denitrification was 2.0 h with a rate of 14.81 mg/(L substrate day). HRT significantly affected the bacterial community structure in DR by changing the population dynamics of the dominant bacteria and denitrifying functional bacteria such as Rhizobiaceae, Desulfovibrionaceae, and Arcobacteraceae. Moreover, the HRT of the DR showed a significant effect on the bacterial community in the nitrification reactor and culture water. Reducing HRT can promote the growth of total bacteria in the DR. However, it revealed a limiting effect on the abundance of key genes of the nitrogen cycle, including the amoA, nirK and nosZ. Under the condition of short HRT, the DR can also achieve a good denitrification effect, which provides feasible management measures for nitrogen removal in RAS.

Biofouling causes a range of problems in aquaculture, and there is a need to validate the effectiveness of antifouling products marketed in the industry. We tested the antifouling performance of four commercial aquaculture netting options at a trout aquaculture operation in the Bras d'Or Lakes, Nova Scotia, Canada. This site has brackish water and a severe mussel (Mytilus edulis) biofouling problem – complete net occlusion can occur within four weeks of the onset of mussel larvae settlement. We tested white and black nylon netting as controls, and four products marketed as having non-toxic antifouling properties: white and black Finsulate®, white Netminder® coating on white nylon netting, and white Dyneema® netting. In 2017, using image analysis measurements of fouling, we found only Netminder® significantly delayed fouling by two weeks over controls. Nonetheless, biofouling on all netting treatments (a mixture of filamentous algae and mussels) reached saturation (i.e. complete net occlusion in the images) within six weeks. After 17 weeks, the Netminder® coated netting supported significantly greater mussel biomass (measured by shell masses). In 2018, a follow-up experiment found that Netminder® caused a one-week delay in exclusively mussel biofouling compared to the white nylon control netting. We conclude that none of the options tested are likely to reduce severe mussel biofouling substantially. However, the benefits of a one-to-two week delay in biofouling caused by Netminder® (including reduced cleaning costs and diminished influence of mussels on water properties and the benthos under the net pens) should be weighed against the cost of application and maintenance for the coating.

The integration of bioremediation systems is one of the most promising techniques to mitigate the environmental impact of aquaculture effluents. Also, it allows nutrient recycling, production diversification, and the creation of high-value by-products. In marine aquaculture, where the implementation of salt-tolerant extractive species is essential, halophyte plants have demonstrated to be optimal candidates for bioremediation of saline aquaculture wastewater. This study aimed to evaluate for the first time the efficiency of Sarcocornia neei (Lag.), a halophyte plant with high adaptability, salinity tolerance and growth potential when irrigated with seawater, in removing nutrients from marine fish aquaculture wastewater and artificial effluents. Two experiments were carried out. In the first one, the growth rate, removal of inorganic nutrients, and accumulation of organic compounds in deep-water hydroponics and sand-substrate systems were evaluated in artificial effluents with different nitrogen and phosphate loads during 70 days. In the second, due to the better performance achieved by S. neei in deep-water systems, its nitrogen removal efficiency and productivity rates were evaluated in deep-water aquaponics with marine aquaculture wastewater and artificial effluents at higher nitrogen loads during 61 days. The highest productivity rates achieved by S. neei (14.41 ± 0.78 kg m−2) were obtained in deep-water culture units, reaching 100% plant survival, suggesting that this species is more suitable for its implementation in this type of system. Significant total ammonia nitrogen removal rates were obtained by the plants, achieving a maximum in sand-substrate systems (0.68 ± 0.41 g m−2 day−1). The results of nitrate removal rates obtained by S. neei (11.25 ± 31.38 g m−2 day−1) make this species an ideal potential candidate for the removal of this compound present in marine RAS effluents. Accumulation of organic compounds was corroborated by obtaining a significant increase (p These results indicated that S. neei is a good candidate for its use as a biofilter for marine aquaculture wastewater. Further investigations should be done to analyze possible influences on growth rates and nutrient removal efficiency by adding essential micronutrients, adjusting effluent salinity, and implementing different plant densities. Also, further studies could be interesting to determine the feasibility of long-term integration of a bioremediation system with S. neei associated with marine aquaculture effluents, approaching its application to industrial-scale production systems.

The oxygen demand, acidification potential, and waste loads of carbon dioxide, nitrogen, and phosphorus from feed were determined for production of channel catfish Ictalurus punctatus, tilapia Oreochromis spp., Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, and whiteleg shrimp Litopenaeus vannamei. Loads of these variables in culture systems (system loads) at typical FCRs ranged from 1090 to 1500 kg t− 1 for feed oxygen demand, 270–440 kg t− 1 for acidification potential, 1186–1885 kg t− 1 for carbon dioxide, 35.9–63.5 kg t− 1 for nitrogen, and 6.1–15.9 kg t− 1 for phosphorus. Using these estimates as representative of feed-based aquaculture and literature data on the proportions of system waste loads typically discharged to the environment (environmental loads), the approximate amounts of waste generated globally by feed-based aquaculture were estimated to be small in comparison to estimates of global anthropogenic waste. Nevertheless, aquaculture should lessen its environmental waste load, and the benefit of improving FCR in reducing waste load was illustrated. Statement of relevance This research will be important in efforts to assess the pollution potential of aquaculture facilities. This will be especially important for aquaculture certification efforts.

Cost effective harvesting of biomass is a major challenge in microalgal industries as it involves the recovery of small sized algal cells from large volumes of culture medium. The present work evaluated the potential of chitosan and aluminium sulfate (AS) in the flocculation of the marine picoalga, Picochlorum maculatum MACC3 using response surface methodology based optimization of flocculation conditions. The viability and integrity of the flocculated cells were assessed using Evan's blue staining and scanning electron microscopy. Under optimized conditions, flocculation efficiency of > 95% was achieved with a chitosan concentration of 63 mg L− 1 at pH 8.5, and aluminium sulfate concentration of 150 mg L− 1 at pH 9.7 with algal biomass concentration of 1.5 g L− 1. Based on flocculation efficiency, cell viability and cell integrity chitosan was selected as an efficient flocculant for biomass harvesting of P. maculatum. The flocculated biomass of this newly isolated nutritionally rich microalga can be further explored for feed applications in aquaculture after accomplishing studies under laboratory and field conditions.

Cost of effluent treatment, water quality maintenance and feeds constitute most of aquaculture's operational costs, and influence its sustainability. The present study examined the effectiveness of periphyton for biofiltration of mariculture effluents. Marine periphyton was allowed to spontaneously develop on a plastic net substrate, in experimental bioreactors that were fed with effluents from fish mariculture ponds. Biomass development and nutrient uptake were followed over four seasons. Attention was given to the orientation and area of the net substrate, season and additional operational factors. The highest specific growth rate (SGR) of 27% day− 1 was measured during the second week of periphyton growth in the summer. Mean daily periphyton production rates in the spring and autumn were 2.4 and 1.8 g (ash-free dry weight) m− 2 day− 1, respectively. The vertical orientation of the net substrate was overall advantageous over the horizontal orientation. Increasing the substrate area of vertically oriented nets in the biofilter increased the removal efficiency of total ammonia nitrogen (TAN) up to 80%, and allowed more biomass production in the biofilter. Multiple polynomial regression models suggest strong effect of biomass weight and effluent retention time on the removal efficiency of TAN and dissolved inorganic nitrogen (DIN). The removal rates of TAN and DIN in these experiments were between 0.11 and 1.2 g N m− 2 (substrate area) day− 1 for periphyton at the age of 7 and 42 days, respectively. Marine periphyton seems to be a simple, low cost and sustainable component, which can perform biofiltration/rehabilitation of water quality and potentially serve as feed for fish and shrimp.

The development of microalgae culture technology has been an integral part of the production of commercially important species in aquaculture. This has been the reason to make great efforts in order to understand several aspects of the microalgae production. The detailed research on monitoring cell growth, which is considered a fundamental part for the use of microalgae in aquaculture, has been, however, overlooked. In this paper, a calibration curve is proposed; correlating the specific absorbance and measured cell density by cell counting (cells mL − 1 ), from four microalgae species important for aquaculture. The final result allows the prediction of cell counting from absorbance using cells mL − 1 = β 1 2 − 4 β 2 β 0 − Abs 1 2 − β 1 / 2 β 2 which is valid for Abs β 0 − β 1 2 /(4 β 2 ). The adjusted determination coefficients ( r 2 adj ) were 0.998, 0.995, 0.991, and 0.998 for Chaetoceros calcitrans , Isochrysis affinis galbana (T-Iso), Nannochloropsis gaditana and Phaeodactylum tricornutum , respectively. The results showed that the obtained equations can be used with an error of less than 5% for microalgae densities of up to 1.01 × 10 7 cells mL − 1 , 2.11 × 10 7 cells mL − 1 , 8.52 × 10 7 cells mL − 1 , and 1.67 × 10 7 cells mL − 1 in the abovementioned species, respectively. Statement of relevance A rapid, simple and specific spectrophotometric methodology for biomass measurements of four microalgae species with high importance in aquaculture was developed. The specific wavelength for the maximum absorbance was established for each of the studied species. With the methodology described here, the harvest time will be easier to identify in facilities where these algae are cultured, and can be also easily tested in other monocultures. In addition, a predictive model was satisfactory and useful for a wide range of cell densities yielding a methodology with high potential for automation. A useful tool was developed for cell counting of microalgae in aquaculture.

Biofilters composed of Ulva or periphyton reveal great potential in removal of excess nitrogen in mariculture effluent while producing protein-rich edible biomass. However, TAN depletion is requisite to improve nitrate removal performance. In the current study we compared the contribution of Ulva fasciata and periphyton in removal of nitrogen, particularly in the form of nitrate, from fishpond effluent. For this purpose, we integrated U. fasciata or periphyton as a secondary biofilter downstream to a primary U. fasciata biofilter, and measured growth and nutrient removal performance in each of these two-step biofilters and in their constitutuent biofiltration units. The upstream U. fasciata biofilters removed nearly all TAN from fishpond effluent, leaving less than 5 μM of TAN but excess NO3-N in the effluent leaving these biofilters for the downstream biofilters. The downstream U. fasciata biofilter removed 76% of NO3-N from its inlet water. While this was about three times more efficient than its periphyton counterpart, the periphyton's specific removal rate of this nutrient (1.5 g NO3-N g−1 DW d−1) was much faster than that of U. fasciata. Overall, integration of two sequenced U. fasciata biofilters (‘Ulva-Ulva’) yielded more biomass and removed more nitrogen than the Ulva-periphyton biofilter (removing 25 vs. 18 g N wk.−1, respectively). Despite the differences in N removal rate and efficiency, the protein level in upstream U. fasciata and downstream periphyton was relatively similar (~25% DW), while somewhat lower in the downstream U. fasciata. Results of the current study favour the two-step U. fasciata biofilter, but periphyton's faster specific removal of NO3-N and its contribution to oxygen generation should not exclude further improvement of this technology.

A high-rate nitrogen removal process is required to maintain the water quality in aquaculture tanks used to produce high-density fish populations in recirculating aquaculture systems. In this study, a combined pilot-scale system of down-flow hanging sponge (DHS) reactors and upflow sludge blanket (USB) reactors was applied as a nitrogen removal system for a longtooth grouper Epinephelus bruneus recirculating aquaculture system. The DHS reactors demonstrated high total ammonium nitrogen (TAN) removal efficiencies and the TAN concentration in the aquaculture tank was maintained at 0.32 ± 0.12 mg-N·L−1. The USB reactor fed with sodium acetate acted as a denitrification unit and adjusted the pH through denitrification reaction. All E. bruneus survived the entire experimental period and the daily weight gain rate of 0.6%·day−1 was comparable to that in marine aquaculture. This result shows that the DHS-USB system to be a novel applicable system for nitrogen removal processes in recirculating aquaculture systems and further study at a large scale should be recommended.

In response to increasing demand for aquaculture products and strict new regulations on organic matter and nitrogen discharge, inland closed recirculating aquaculture systems (RASs) are being developed as a viable eco-sustainable alternative to traditional aquaculture (e.g. ponds, raceways and cages) because of their minimal environmental impact and controlled operation. Fish feed is virtually the only source of carbon and nitrogen to the system. It is estimated that 20 to 30% of the feed nitrogen and 50% of the feed carbon are assimilated or utilized by the fish, while the rest is released to the water. Understanding the fate and utilization of these elements can help optimize RAS efficiency and economics. The fate of carbon and nitrogen was studied by mass balance in a novel near-zero discharge ( 2 and the rest (5%) remained as nondegradable carbon in the UASB. Using the UASB can save up to 12% of the system's energy demands, both directly as energy (methane) input and indirectly by reducing the system's oxygen demand. Of the feed nitrogen, 29% was assimilated by the fish and bacteria in the nitrification reactor and 40–50% was removed in the denitrification reactor, of which 10–20% was removed by anammox. Lastly, ~ 20% of the nitrogen was removed in the UASB reactor, likely by precipitation. It was demonstrated that the system was operating at high stocking density, with almost complete nitrogen and carbon removal and energy recovery. Statement of relevance The fate of carbon and nitrogen was studied by mass balance in a novel near-zero discharge (

The accuracy and precision of different methods for detecting the endpoint of the total alkalinity titration and the typical accuracy and precision obtained for alkalinity analyses by a large sample of laboratories were investigated. The optimum, endpoint for total alkalinity titrations decreased from pH 5.0 at 10 mg l − 1 alkalinity to pH 4.2 for 300 mg l − 1 alkalinity or more. The appropriate color changes for bromocresol green-methyl red (BG-MR) and methyl orange (MO) indicators also varied with the initial total alkalinity of samples. Despite differences in pHs at endpoints for samples of different alkalinities, when the best endpoint pH, best color of BG-MR and MO, or the endpoint of methyl purple were used in titrations of standard solutions, there were few differences between measured alkalinities and standard alkalinities — the accuracy was better than ± 3 mg l − 1 . Results of spike and recovery tests on aquaculture pond water samples also revealed that an accuracy of ± 3 mg l − 1 alkalinity could be achieved on either unfiltered or filtered samples by all four methods of acceptable endpoint detection. Although precision of measurements could not be consistently maintained below ± 1 mg l − 1 , coefficients of variation for repeated measurements usually were less than 3% for all methods of endpoint detection. Nevertheless, this degree of precision was adequate to achieve good accuracy that is the major concern in water analysis. Variations in alkalinity measurement that could result from improper selection of endpoint pH (or color) were rather small — usually not more than ± 5 mg l − 1 . In an interlaboratory comparison of alkalinity determinations on standard solutions, most laboratories reported inaccurate alkalinities. These inaccuracies were greater than possible endpoint variations. The most likely sources of error contributing to poor results by the different laboratories were improperly standardized acid for alkalinity titrations, reliance on burets or other titrating devices with coarse calibrations, and use of excessively small sample volumes. Moreover, it was clear that most of the participating laboratories did not have a satisfactory method of quality control. Statement of relevance Alkalinity is important as a source of carbon for photosynthesis, as a buffer, and as a general index of productivity. Thus, it is often measured, but by several different methods of endpoint detection. This study provides useful information of the reliability of alkalinity analyses and recommends how to maintain acceptable precision and accuracy of the procedure.

Nitrate is typically removed from aquaculture effluents using heterotrophic denitrification reactors. Heterotrophic denitrification reactors, however, require a constant input of readily available organic carbon (C) sources which limits their application in many aquaculture systems for practical and/or economic reasons. A potential alternative technology for removing nitrate currently applied for treating surface and drainage water is based on using wood by-products as a carbon source for denitrification. Using lab-scale horizontal-flow woodchip filters, the current study investigated the potential of optimizing woodchip reactors for treating aquaculture effluent. A central composite design (CCD) was applied to assess the effects of simultaneously changing the empty bed contact time (EBCTs of 5.0–15.0 h; corresponding to theoretical hydraulic retention times of 3.3–9.9 h) and bicarbonate (HCO 3 − ) inlet concentration (0.50–1.59 g HCO 3 − /l) on the removal rate of NO 3 − N, and additional organic and inorganic nutrients, in effluent deriving from an experimental recirculating aquaculture system (RAS). Volumetric NO 3 − N removal rates ranged from 5.20 ± 0.02 to 8.96 ± 0.19 g/m 3 /day and were enhanced by adding bicarbonate, suggesting that parts of the removal was due to autotrophic denitrification. The highest N removal rate (8.96 ± 0.05 g/m 3 /day) was achieved at an EBCT and HCO 3 − combination of 15 h and 1.59 g HCO 3 − /l. Bicarbonate inlet concentration as a single factor had the strongest effect on N removal rates followed by the interaction with EBCT, and EBCT 2 (quadratic term). The study thus indicates that woodchip beds may be applied and optimized for removing nitrate from aquaculture effluents. Statement of relevance This study is a relevant contribution to research in aquaculture as it presents an alternative method for removing nitrates from aquaculture effluents especially for less intensive fish farms. Furthermore, it shows how this method can be optimized to yield higher removal rates of nitrate.

Environmentally responsible disposal of solid organic wastes from land-based brackish and marine recirculating aquaculture systems is critical for promoting widespread acceptance and implementation, but conversion efficiency of saline sludge to biomethane is generally low. We describe the development of a microbial consortium that can convert marine organic fish waste solids to biomethane at over 90% efficiency. The halotolerant microbial consortium, which was developed by sequential transfer in seawater with fish waste, is optimized for low COD:N ratios typical of organic fish waste and does not require addition of amendments such as organic carbon or nutrients. Temperatures for maximum rates of conversion range from 26 to 35 °C. Five predominant phylotypes identified in the microbial consortium by denaturing HPLC were isolated. Two isolates included anaerobic fermentative bacteria identified as a strain of Dethiosulfovibrio and a strain closely related to Fusobacterium spp., which both hydrolyze and ferment proteins, peptides and amino acids. The other three isolates included an acetate-utilizing methanogenic archaeon identified as a strain of Methanosarcina and two hydrogen-utilizing methanogenic archaea identified as strains of Methanogenium and Methanoplanus . Bioconversion rates of sterile fish waste with the reconstituted microbial consortium containing all five isolates were equivalent to rates observed with the original enriched consortium after one sequential transfer. The results demonstrate unequivocally that halotolerant consortia of bacteria and archaea can be developed for bioconversion of saline organic solid waste with high efficiencies equivalent to those attained with non-saline waste systems. Understanding the microbial community composition is critical for management of solid organic waste from land-based marine aquaculture systems and to maintain or restore microbiota during start up and throughout the production process. Statement of relevance Appropriate disposal of solid organic wastes from land-based brackish and marine recirculating aquaculture systems is critical for promoting widespread acceptance and implementation. We demonstrate that halotolerant consortia of bacteria and archaea can be developed for bioconversion of saline fish waste with high efficiencies equivalent to those attained with non-saline waste systems.

Recirculating aquaculture systems (RAS) using biofloc biofilters can address the high accumulation of nitrate (NO3−-N) and total suspended solids (TSS) in in-situ biofloc technology (BFT) aquaculture systems. A RAS was divided into the following four zones: reaction zones of the BFT biofilters, settling zones of the BFT biofilters, culture tanks, and a buffer tank. During the 95-day experimental period, the water quality parameters and microbial communities in different zones of the RAS were compared. The NO3−-N, nitrite (NO2−-N), total ammonia nitrogen (TAN), and TSS in the culture tanks were continuously controlled at average concentrations of 9.84 ± 5.15, 0.28 ± 0.15, 0.10 ± 0.18, and 96.92 ± 33.82 mg·L−1, respectively. Because denitrification produced alkalinity in the BFT biofilters, the alkalinity of the culture tanks reached an appropriate concentration of 109.40 ± 10.57 mg CaCO3·L−1 without intentional adjustment. The concentrations of NO3−-N, NO2−-N and TAN in the reaction zones were significantly lower than those in the influent (buffer tank) and culture tanks. However, there was no significant difference found for major water quality parameters between the reaction zones and the settling zones. There was also some removal of soluble reactive phosphate by the BFT biofilters, although there was no significant difference between the biofilters and influent. Microbial communities in the reaction zones were more diverse than those in the culture tanks, buffer tank and settling zones. Denitrifiers, nitrifying bacteria and important functional microbial populations for phosphorus removal were all present in the reaction zones, and at higher levels than those in other zones. Nitrogen and phosphorus removal were mainly achieved in the reaction zones of the BFT biofilters, and the microbial communities in the other three zones were similar. Besides, Scortum barcoo grew from an individual weight of 347.7 ± 73.0 to 472.1 ± 106.2 g, achieving a final stocking density of 32.81 kg·m−3 at the end of the experiment.

The presence of high concentrations of ammonia, nitrite, and nitrate is a big challenge for the aquaculture industry to sustain fishery production, hence need to be treated in an economically feasible and environmentally friendly way. In the present study, a consortium of three bacterial isolates I4, I6, and I12, identified as Bacillus cereus, Bacillus amyloliquefaciens, and Pseudomonas stutzeri respectively, were assembled for the biodegradation of ammonia and nitrite in aquaculture wastewater. The consortium was employed as a bioaugmentation agent in tanks stocked with Oreochromis mossambicus fingerlings. During the experimental period of 15 days, under controlled conditions of temperature and light, the values of tested parameters were found to be increasing in both treatment and control tanks. The residual concentration of ammonia in the tanks treated with the consortium was always lower (4.8 ± 0.068 μML−1) than that of the control tanks without any bacteria (7.29 ± 0.292 μML−1). Increased residual concentration of nitrite and nitrate in the treatment tanks (6.9 ± 0.59 and 4.16 ± 0.58 μML−1 respectively) compared to the control tanks (0.28 ± 0.201 and 0.394 ± 0.964 μML−1 respectively) confirmed the efficiency of the consortium to convert ammonia to nitrite and further to the less toxic nitrate. Moreover, their values were never reached to the toxic level in the treatment tanks with a survival rate of 97.2 ± 0.58%, whereas in the control tanks death of fishes due to ammonia toxicity was observed (55 ± 0.25%). The study proved that the microbial consortium of Bacillus cereus, Bacillus amyloliquefaciens, and Pseudomonas stutzeri was efficient in reducing ammonia, nitrite, and nitrate in aquaculture wastewater and hence can be employed as a bioaugmentation agent to above-mentioned parameters in the aquaculture wastewater before discharging into the open system to reduce the environmental problems as well as to reuse the water.

Marine pollution from aquaculture wastewater is a widespread and increasing ecological problem. Algae, with their ability to remove surplus nutrients from wastewater, are a good tool for achieving more sustainable aquaculture. In this study, the capability of different biomasses of Chaetomorpha linum and Cladophora prolifera for the bioremediation of nutrient-rich (ammonium, nitrate and phosphate) seawater was compared. The results suggest that 10 g L−1C. linum is an excellent candidate for aquaculture wastewater bioremediation. However, the bioremediation efficiency of C. linum was significantly affected by seasonality, with the greatest performance in nutrient removal exhibited by algae harvested in summer. C. linum harvested in winter and acclimated to lab conditions for two months, significantly improved the removal efficiency of both ammonium and nitrate, while worsening that of phosphate. Irrespective of season and acclimation, the simultaneous presence of ammonium and nitrate in seawater strongly inhibited nitrate removal. Thus, we propose the use of a two-step system, tested at the laboratory scale, in which nutrient-enriched seawater can pass through two different algal ponds. C. linum was able to achieve almost complete removal of ammonium in 24 h in the first step, while the second step improved both nitrate and phosphate removal efficiency. The two-step system is an effective innovation for the use of algae in bioremediation of aquaculture wastewaters.

Removal of total ammonium nitrogen (TAN) is essential during transportation of live seafood due to its high toxicity to aquatic cultures. Recirculating TAN removal system has been proposed and installed for the transportation of live seafood, while TAN removal performance often deteriorates at low temperature range (10–20 °C) due to the decrease of nitrifying activity. The authors have previously developed down-hanging sponge (DHS) reactors as a recirculating TAN removal system, which is a trickling filter system that uses polyurethane-sponge media to retain nitrifying biomass. The present study aimed to examine TAN removal performance of DHS reactor operated at 10 and 20 °C, and the following 4 DHS reactors were operated for the purpose; the DHS reactor operated 1) at 20 °C, 2) at 20 °C with addition of powdered activated carbon (AC) as an additional biomass carrier, 3) at 10 °C, and 4) at 10 °C with AC (designated as 20 °C-DHS, 20 °C-DHS-AC, 10 °C-DHS, and 10 °C-DHS-AC reactors, respectively). The DHS reactors were operated for 472 d with feeding of artificial seawater media, and TAN loading rates increased stepwisely up to 200 mg-N L-sponge media−1 d−1. TAN removal performance was examined by determining the concentrations of TAN, nitrite and nitrate in influent and effluent. Additionally, amplicon sequencing of prokaryotic 16S rRNA gene sequence was performed at Day 34, 212 and 374 to identify the nitrifying bacteria involved in the TAN removal. Both the 20 °C-DHS and 20 °C-DHS-AC reactors showed 200 mg-N L-sponge media−1 d−1 of TAN removal rate, whereas the 10 °C-DHS reactor showed only 15 mg-N L-sponge media−1 d−1. Notably, the addition of AC enhanced TAN removal performance of the DHS reactor operated at 10 °C. The 10 °C-DHS-AC reactor showed 60 mg-N L-sponge media−1 d−1 of TAN removal rate, which was 4-folds higher than those found in the 10 °C-DHS reactor. The amplicon sequencing analysis revealed that ammonia-oxidizing (i.e., Nitrosomonas) and nitrite-oxidizing (Nitrospira and Nitrospina) bacteria (AOB and NOB, respectively) proliferated in the operated DHS reactors, and the relative abundance of those AOB and NOB were greater in the DHS reactors with AC addition (i.e., the 20 °C-DHS-AC and 10 °C-DHS-AC reactors). Intriguingly, temperature difference (20 °C and 10 °C) resulted in occurrence of different NOB communities, and Nitrospira and Nitrospina were prominent in the DHS reactors operated at 20 °C and 10 °C, respectively. DHS reactor is capable of removing TAN even at 10 °C, which is applicable as a recirculating TAN removal system for transportation of live seafood.

Disease outbreaks are a major concern in aquaculture. This is particularly true in intensive recirculating aquaculture systems (RASs), due to the high rearing densities in a system where high concentrations of organic matter are produced with minimal water exchange. This study assessed the survivability of the common fish pathogen Streptococcus iniae in a solid-removal unit of a RAS, the upflow anaerobic sludge blanket (UASB). A PCR detection method, along with an improved protocol for the extraction of high-quality DNA from sludge samples, were utilized for this purpose. This method enabled detection of S. iniae at a minimum concentration of 7.6 × 10 5 CFU mL − 1 raw sludge. We examined the survivability of S. iniae in batch digesters, which consisted of sealed serum bottles filled with sludge from the UASB reactor, and in laboratory-scale flow-through UASB reactors that were continuously fed with fish waste sludge. Results demonstrated a gradual decrease in the intensity of the PCR-amplified product to the point of no detection in either batch or UASB digesters, suggesting that the conditions present in the UASB reactor are not favorable for S. iniae . The PCR-based detection method was successfully applied to sludge from a commercial RAS enabling detection of potentially pathogenic bacteria. Statement of relevance The manuscript addresses the control of bacterial disease-causing agent in a near-zero discharge aquaculture system which contains a novel solid removal unit. The bacteria studied is S. iniae , a significant disease-causing agent in aquaculture. The potential threat of disease outbreaks increases with the intensification of the culture system, such as the one described and analyzed in this study. This intensification is of high relevance to the industry, as it reduces environmental contamination due to fish production as well as enables fish culture in places distant from a natural water source.

The aquaculture industry needs a stable supply of feed resource materials in sufficient quantities and quality for future growth, in particular the fatty acids eicosapentaenoic acid (dha) and docosahexanoic acid (DHA) which so far have been ensured by inclusion of fish oil. About 70% of the available fish oil is being used in aquafeeds, but the global supply of fish oil is limited and emerging omega-3 markets are competing with the aquaculture industry for this valuable resource. New sources of dha and DHA must be fully developed to cover the global demand, and marine microalgae are regarded as a promising alternative as the primary producer of all the EPA and DHA in marine food webs. Industrial cultivation of phototrophic microalgae is conducted in open pond systems or closed photobioreactor systems, designed to maximize the utilization of light energy and to achieve efficient uptake of nutrients and CO 2 . The economics of microalgae production heavily depend on the photosynthetic productivity, and there are ongoing efforts to increase the microalgae productivity following different strategies. The first is to exploit the cultivation conditions to direct the metabolism towards lipid production. The second is to improve biomass productivity or lipid yield by mutagenesis and selective breeding, and the third strategy is to improve strains by genetic modifications to optimize light absorption and increase the biosynthesis of EPA and DHA. The inclusion of whole microalgae cells in aquafeeds will require sufficient processing to ensure maximum nutritional uptake, involving dewatering and cell disruption in order to maximize the bioavailability of nutrients. The roadmap of microalgae to become a sustainable aquafeed resource must include interdisciplinary research and development efforts along the whole value chain to achieve biomass production in an industrial scale. A techno-economic analysis of microalgae production was conducted based on biological and technical parameters from the literature under various scenarios, showing that biological productivity, geographical locations and production technology are important factors to lower production cost. The production cost of EPA and DHA equivalents revealed the lowest cost for flat panel photobioreactors in locations with clear sky conditions. Sensitivity analysis showed that optimizing photosynthetic efficiency and doubling of the EPA and DHA yield could reduce the cost to 11.9 USD per kg of total EPA and DHA equivalents. Our findings suggest that focused research efforts can contribute to achieve economically sustainable production of microalgae rich in EPA and DHA for use in aquafeed in the near future.

Denitrification on internal carbon sources offers the advantage to control nitrate levels in recirculating aquaculture systems (RAS) by using the fecal carbon produced within the husbandry system. However, it is not clear to which extent fecal carbon can be utilized by the microbial community within a denitrification reactor. Especially fibers can hamper the bioavailability of carbon in fecal waste. Therefore, this study investigated the nitrogen removal capacity of a denitrification reactor using fecal waste with a high fiber content as the only carbon source in RAS. Furthermore, we investigated to which extent fibers were utilized as a carbon source within the reactor. Four identical small-scale RAS (V = 460 L) were stocked with 25 rainbow trout of ~ 110 g, and operated at a water exchange rate of ~ 200 L/kg of feed DM. Two RAS served as controls without denitrification and two RAS were upgraded with an upflow sludge blanket denitrification reactor (V = 10.5 L). During the six weeks of experiment, we determined COD (chemical oxygen demand, measure for organic carbon) and N balances for all systems and analyzed the composition of the collected solids. The denitrification reactors were able to remove 19 g N/kg of feed DM, or 48% of the metabolic nitrogen waste produced by the fish. Based on the COD balances, 44% of the supplied fecal COD was degraded in the reactor. Hemicellulose and cellulose degradability was ~ 50%, accounting for 45% to the total degraded COD. Under steady state conditions, 4.4 g of biodegradable COD needed to be oxidized to reduce 1 g of nitrogen, indicating respiratory COD losses of approximately 50%. This experiment successfully demonstrated that denitrification on internal carbon sources using a high fiber diet could remove half of the nitrogen waste produced by the fish. Although fibers limited carbon bioavailability, half of the cellulose and hemicellulose present in the fecal waste was utilized in the denitrification reactor.

The lime requirement of ponds can be determined by direct titration with standard sulfuric acid of the amount of alkalinity neutralized by the exchangeable acidity displaced from a bottom soil sample equilibrated with a solution of 1.0 N in potassium ion and 0.04 N in bicarbonate (2 mg CaCO3 equivalent mL− 1). This procedure, called the K-bicarbonate method here, provided precise estimates of lime requirement that were 9.6% to 27.2% (average = 12.9%) greater than those obtained by the method currently recommended for use on pond soils. It is likely that the K-bicarbonate method neutralizes more of the exchangeable acidity in pond bottom soil samples than does the current method recommended for pond bottom soils and thereby provides a more reliable estimate of lime requirement. Moreover, the K-bicarbonate method does not require a hazardous chemical, a mechanical shaker, or a pH meter as does the current method for pond lime requirement. The cost per analysis also is cheaper by the K-bicarbonate method than with the method currently recommended for pond soils.

article i nfo Seaweed IMTA biofilter Ulva lactuca Aeration Economics A strong aeration evens out light exposure, facilitates solute diffusion and increases yield in macroalgae cultivation. It is also responsible however, for up to 85% of the operating cost in the treatment of fish pond effluents. Optimizing and reducing excess aeration can therefore diminish the overall operation cost in monoculture and in Integrated Multi Trophic Aquaculture (IMTA). Biofiltration efficiency and crude biochemical composition of Ulva lactuca ponds were compared at two aeration regimes (continuous and 15 s min -1 intermittent aeration) in

There is a critical need in U.S. public aquaculture and fishery management programs for an immediate-release sedative, i.e. a compound that can be safely and effectively used to sedate fish and subsequently, allow for their immediate release. AQUI-S® 20E (10% active ingredient, eugenol; any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government) is being pursued for U.S. approval as an immediate-release sedative. As part of the approval process, data describing animal safety and efficacy are needed. Essential to conducting studies that generate those data, is a method to accurately and precisely determine AQUI-S® 20E concentrations in exposure baths. Spectrophotometric and solid phase extraction (SPE)–high pressure liquid chromatography (LC) methods were developed and evaluated as methods to determine AQUI-S® 20E (eugenol) concentrations in water, methods that could be applied to any situation where eugenol was being evaluated as a fish sedative. The spectrophotometric method was accurate and precise (accuracy, > 87%; precision, 86%; precision

The rapid removal of suspended solids from aquacultural systems is of utmost importance in maintaining healthy stock and system stability and in addressing environmental concerns. This research tested a new approach, successfully manipulating fecal density to the point of floatation. Fecal casts floating at the water's surface can be transported quickly to a removal device. The speed of removal minimizes opportunity for leaching, and exposure to shear forces and turbulence caused by mechanical devices and fish motion. Waste thereby persists as larger particles, which are easier to remove by traditional microscreens or skimming apparatus. Four different low-density feed additives were tested in different dosages and gradings on duplicate groups of rainbow trout, in order to appraise the effects on fecal density, and on growth and health of fish stock. The control groups received the same basal diet without additives, which resulted in fecal densities in the upper ranges expected for commercial trout diets at 1.04 g cm − 3 and 1.05 g cm − 3 for water-soaked and intestinal feces, respectively. Five of the additive diets significantly reduced the density of both intestinal and water-soaked feces, with the most effective (cork; 0.5–1 mm; 2%) leading to floating feces (4.39% to 1.00 g cm − 3 and 5.12% to 0.98 g cm − 3 for intestinal and water-soaked feces, respectively). The larger grade of cork granules performed significantly better than the smaller grade. The possibilities for reducing levels of effective cork incorporation and enhancing effects on density by other quality improvements are discussed. Feed efficiency and fish health were not impaired by the additives. It is suggested that the systematic manipulation of fecal density with low-density additives may achieve economic and ecological advances and offer a new and effective means of managing and optimizing waste output from aquaculture. The effects of floating feces on removal efficiency, leaching effects, water quality and operating costs in aquacultural systems have to be further explored.

Bivalve aquaculture currently utilizes two main farming practices: intertidal (beach) and deep-water (suspended) culture. Although suspended culture offers a number of advantages during both nursery and grow-out phases, two commonly encountered issues – shell deformities and biofouling – lead to reduced seed and final product quality in some species and preclude other species from being cultured in suspension. None of the existing strategies for controlling these issues is efficient and fully reliable. In this study we tested the efficiency of two new methods for controlling biofouling and shell deformities in suspended culture of bivalves using basket cockle Clinocardium nuttallii as a model species. The first method involved a short-term increase in bivalve stocking density during peak plankton concentrations and biofouling settlement periods. The second method comprised adding artificial growth medium (expanded clay aggregate) to culture enclosures. Both high-density and growth medium treatments significantly reduced the incidence of C. nuttallii shell deformities compared to the control treatment (by 86 and 72%, respectively). This finding suggests that clam shell deformities in suspended culture primarily develop due to the lack of structural support normally offered by the substratum. Both treatments also significantly reduced barnacle fouling rate (by 67 and 83%, respectively). Additionally, growth medium treatment led to a significant reduction in tube worm fouling, as well as combined fouling rate and intensity, but it was less effective in controlling sponge fouling. Overall, both high-density and growth medium treatments showed promise in reducing the incidence of shell deformities and the amount of biofouling on C. nuttallii in suspended culture. These treatments are inexpensive, environmentally-friendly, readily available to shellfish growers, and may be further refined and adapted for a variety of cultured bivalve species. They have the potential to improve the efficiency of suspended grow-out systems and extend the option of suspended culture to bivalve species currently grown on the beach only.

Minimal-exchange, intensive culture systems require little, if any, water exchange and have high animal stocking densities. Intensive nutrient inputs lead to an abundant community of microorganisms. These microbes are partially contained within suspended “biofloc” particles and contribute to water quality maintenance and provision of supplemental nutrition to the culture species. Optimal function of minimal-exchange, intensive systems is likely dependent on the structure of the microbial communities within them. This document offers a short review of microbial groups important for intensive marine aquaculture and descriptions of three methods for quantifying their abundance. The document also describes an experiment during which these methods were used to monitor the effects of partial biofloc removal on microbe abundance. The first method uses light microscopy, with the option of epifluorescence, along with a ranking system to enumerate the abundance of microbial taxa. The second method exclusively uses epifluorescence to illuminate chlorophyll and cyanobacteria pigments. Images are taken of each fluorescing group of pigments and processed using image analysis software to quantify the respective abundance of the two pigment types. Using the third method, changes in bacterial abundance were determined by gas chromatographic measurement of bacteria-specific fatty acids in solvent extracted water column lipids. Using these techniques, it was determined that removing solids from the culture water significantly (P ≤ 0.01) reduced the abundance of nematodes, rotifers, cyanobacteria, and bacteria. Understanding microbial composition and the effects that management protocols have on that composition may help system managers make better informed decisions.