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1.
Steroid hormones have been shown to accumulate in recirculation aquaculture system (RAS) water over time; however, their influence on the reproductive physiology of fish within RAS remains unknown. Whether ozonation impacts waterborne hormone levels in RAS has likewise not been fully evaluated. To this end, a controlled 3-month study was conducted in 6 replicated RAS containing a mixture of sexually mature and immature Atlantic salmon Salmo salar to determine whether ozone, as typically applied in RAS to improve water quality, is associated with a reduction in waterborne hormones. Post-smolt Atlantic salmon (1253 ± 15 g) were stocked into each RAS; 109 of 264 fish placed in each system were sexually mature males, and 5 were mature females. Water ozonation, controlled using an ORP set-point of 290–300 mV, was applied with the pure oxygen feed gas within the low-head oxygenators of 3 randomly selected RAS, while the remaining 3 RAS did not receive ozone. The RAS hydraulic retention time was 6.9 ± 0.3 days. Study fish were raised under these conditions for 12 weeks; during weeks 10 and 12, triplicate water samples were collected from the following locations in each RAS: i) culture tank, ii) makeup water, iii) pre-biofilter, iv) post-biofilter, and v) post-gas conditioning. Concentrations of 3 waterborne hormones – testosterone, 11-ketotestosterone (11-KT), and estradiol (17β-estradiol) – were quantified using enzyme immunoassays (EIA). Estradiol was significantly reduced by ozonation; testosterone and 11-KT were also reduced by ozonation, although these reductions were not observed across all sampling locations and events. Testosterone and 11-KT concentrations, however, were significantly reduced following water passage through the biofilters of both ozonated and non-ozonated RAS. The results of this study demonstrate the potential for ozone to be used in RAS as a means of preventing the accumulation of steroid hormones. Further research is required to assess whether reducing hormones in this manner impacts precocious sexual maturation in RAS-produced Atlantic salmon. 相似文献
2.
Turbot, Psetta maxima, represent a valuable and growing subsector of global finfish aquaculture, although bacterial infections such as edwardsiellosis have adversely affected the industry in recent years. During an experiment designed to investigate the effect of direct ozonation on fish performance in RAS, a bacterial disease outbreak (Edwardsiella tarda) occurred, presenting an opportunity to record additional effects of experimental ozonation regimes on performance of turbot grown in RAS. This short note thus collates phenomenological information on survival, growth and water quality parameters recorded during a 91 day experiment with juvenile fish. Alongside antibiotic therapy, a high ozone treatment (360 mV) improved survival of stock compared to those in a non-ozonated control (200 mV) and significantly so compared to low ozone treatment (320 mV). Both experimental treatments reduced total heterotrophic and Vibrio sp. bacterial loading and nitrite concentration in culture water compared to the control. Experimental ozone treatment also suggested a trend for improved growth and feed intake. Although no confirmed link or mechanism between ozonation and reduced impacts of bacterial infection are proven in this study, the observations add further evidence to the body of work demonstrating beneficial effects of ozonation on water quality, survival and growth of farmed fish. 相似文献
3.
In recirculating aquaculture systems (RAS), the crucial step of eliminating toxic N compounds like ammonia and nitrite is mediated via nitrifying microorganisms and takes place in biofilters. In this study, analyses of microorganisms colonizing biocarriers of nine moving-bed biofilters of three different RAS operated with freshwater, brackish or marine process water uncovered site specific communities. Illumina-based amplicon sequencing of the V4-region of the 16S rRNA gene revealed a high microbial diversity with 1000–2500 species-level operational taxonomic units (OTUs) in all biofilters with the highest diversity in the brackish RAS. Proteobacteria, Bacteriodetes, Plantomycetes, Chloroflexi and Nitrospirae represented the most abundant phyla. 76 out of 674 known genera occurred in all nine biofilters and were defined as core-taxa, including nitrifying bacteria (Nitrosomonas and Nitrospira) as well as members of the (heterotrophic) genera Planctomyces, Blastopirellula, Nannocystis and Lewinella. Nitrifying communities composed of different, closely related and so far uncultured members of Nitrosomonas and Nitrospira were identified, strongly indicating that several potentially novel ammonia and nitrite oxidizing species are present in RAS biofilters. Relatives of known comammox Nitrospira were detected in the brackish biofilters, revealing 94–99 % identity of the 16S rRNA gene sequence to Ns. inopinata. Salinity tolerance tests with biocarriers derived from biofilters of the three distinct RAS showed an unexpected broad physiological flexibility with regard to salinity. Nitrification performance of freshwater nitrifiers was drastically reduced with increasing salinity and nearly completely inhibited at 15 PSU, while the brackish and marine nitrifiers showed a high resistance and maintained nitrification activity in a broad range of salt concentrations. This data can help to improve the nitrification process in RAS with changing salinity of the process water. 相似文献
4.
Biological filtration, or biofiltration, is the key technology in recirculating aquaculture systems. Sequencing microbead biofilters, in which the media maintains a continuous up-and-down movement, are based on traditional microbead filters but offer superior filtration properties. The performance characteristics of a sequencing microbead biofilter installed in a recirculating aquaculture system for rearing Barcoo perch at 29 ± 1 °C were examined. The total ammonia-nitrogen (TAN) concentrations and the nitrite-nitrogen concentrations during a 52-day culture period were maintained blow 1.6 mg/L and 0.9 mg/L. In order to ensure efficient biofiltration, the optimal actual application of hydraulic retention time was determined to be approximately 3–5 min. The water flow produced by the reciprocating motion of the media served to wash away suspended solids, ensuring the occurrence of optimal nitrification processes. Additionally, the reciprocating motion of the media enhanced ammonia treatment efficiency significantly by improving the transport of nutrients and nitrification activity. Compared to a static situation the ammonia removal rate increased by 27% based on the application of up-and-down reciprocating movement. The biofilm on the microbead forms as a compact, complex, and homogeneous structure, consisting of numerous microscopic thin sheets. Additionally, a multitude of pores, interstitial voids, and vertical channels were widely observed to convey obviously advantageous properties in support of fluid passage, thus enhancing mass transfer and ultimately contributing to biofiltration effectiveness. The optimum biofilm thickness for providing efficient biofiltration was determined to be approximately 70 μm for this filter. 相似文献
5.
Particulate and dissolved nitrogen (N) waste components are removed in recirculating aquaculture systems (RAS) using different cleaning technologies, and to dimension and optimize their removal efficiency requires that the expected daily load of the different waste forms can be estimated. Using a laboratory, mass-balance approach, the current study examined the effects of commercially applied feeding levels on the loading of different N waste forms, including daily fluctuations in dissolved total nitrogen (TN), total ammonia nitrogen (TAN), urea-N, and non-characterized, dissolved N deriving from juvenile rainbow trout (Oncorhynchus mykiss). In addition, the study examined whether there was a removal of urea-N across a moving bed biofilter operated as end-of-pipe under commercial conditions. The laboratory, mass-balance study showed that there were no effects of feeding levels (1.3, 1.5 or 1.7% of the biomass per day ) on the excretion of dissolved N components, which constituted the majority of total N waste (>81.6% on average). The excretion of urea-N and non-characterized, dissolved N components constituted 12–13% and 9–11%, respectively of dissolved TN. The excretion of urea-N was largely constant and independent of the daily feeding practice, whereas that of non-characterized N appeared to reflect the daily feeding activity, following the trends in TN and TAN. The time limited feeding regime applied in the laboratory study resulted in a pulse in the excretion of TAN that a biofilter may be unable to fully level out, potentially resulting in unnoticed, critical water quality conditions in intensive RAS during certain times of the day. Particulate N waste constituted a minor fraction of total N waste (<18.4% on average), and the actual loading depended on the digestibility of dietary protein/nitrogen. Results from the commercially operated, nitrifying biofilter showed that urea-N was removed at a rate of 0.014 g N m2 day−1. Compared to the removal of TAN (0.208 g N m2 day−1), the moving bed biofilter was 1.07 times more active in removing dissolved N than immediately expected when only considering TAN. 相似文献
6.
Steven T. Summerfelt Mark J. Sharrer Scott M. Tsukuda Michael Gearheart 《Aquacultural Engineering》2009,40(1):17-27
A continuous water disinfection process can be used to prevent the introduction and accumulation of obligate and opportunistic fish pathogens in recirculating aquaculture systems (RAS), especially during a disease outbreak when the causative agent would otherwise proliferate within the system. To proactively prevent the accumulation of fish pathogens, ozonation and ultraviolet (UV) irradiation processes have been used separately or in combination to treat water in RAS before it returns to the fish culture tanks. The objective of the present study was to determine the process requirements necessary to disinfect the full RAS flow, using ozonation followed by UV irradiation, just before the flow was returned to the fish culture tank(s). We found that a proportional-integral (PI) feed-back control loop was able to automatically adjust the concentration of ozone (O3) generated in the oxygen feed gas (and thus added in the low head oxygenator) in order to maintain the dissolved O3 residual or ORP at a pre-selected set-point. We determined that it was easier and effective to continuously monitor and automatically control O3 dose using an oxidative reduction potential (ORP) probe (in comparison to a dissolved ozone probe) that was located at the outlet of the O3 contact chamber and immediately before water entered the UV irradiation unit. PI control at an ORP set-point of 450 and 525 mv and a dissolved O3 set-point of 20 ppb provided almost complete full-flow inactivation of heterotrophic bacteria plate counts (i.e., producing <1 cfu/mL) and improved water quality (especially color and %UVT) in a full-scale recirculating system. Achieving this level of treatment required adding a mean dose of approximately 29 ± 3 g O3 per kg feed. However, because water is treated and reused repeatedly in a water reuse system, the mean daily O3 demand required to maintain an ORP of 375–525 mV (or at 20 ppb dissolved O3) was 0.34–0.39 mg/L, which is nearly 10 times lower than what is typically required to disinfect surface water in a single pass treatment. These findings can be used to improve biosecurity and product quality planning by providing a means for continuous water disinfection in controlled intensive RAS. 相似文献
7.
循环海水养殖系统硝化滤器中氨氧化微生物分析 总被引：2，自引：0，他引：2
研究循环水养殖硝化滤器载体上附着生物膜的微生物群落结构可以为提高其处理速率和效率,并为特异性工程菌构建提供依据。采用改良的AFLP方法分析了循环水养殖硝化滤器载体上附着的氨氧化细菌16S rRNA基因和氨单加氧酶amoA基因片段及其系统发育情况。结果表明:分析16S rRNA基因得到的序列片段比分析amoA基因片段得到了更多信息,准确度较高,可作为分析循环水养殖硝化滤器氨氧化菌群组成的有效方法。克隆测序所得序列与网上公布数据比对,可见存在于循环水养殖硝化滤器载体上的氨氧化细菌与Nitrosomonas cryotolerans、Nitrosomonas oligotropha、Nitrosospira tenuis、Nitrosomonas marina相似度达100%,与Nitrosomonas aestuarii相似度为87%。大部分属于亚硝化单胞菌属(Nitrosomonas),仅少数序列属于亚硝化螺菌属(Nitrosospira)。采用16S rRNA基因和amoA片段分析方法得到的附着于封闭循环海水养殖硝化滤器载体上的氨氧化细菌主要为变形菌(Proteobacteria)的β-亚类的亚硝化单胞菌属(Nitrosomonas)和少量的亚硝化螺菌属(Nitrosospira)氨氧化细菌,以及一定数量的γ-亚类氨氧化细菌。 相似文献
8.
When operating water recirculating systems (RAS) with high make-up water flushing rates in locations that have low alkalinity in the raw water, such as Norway, knowledge about the required RAS alkalinity concentration is important. Flushing RAS with make-up water containing low alkalinity washes out valuable base added to the RAS (as bicarbonate, hydroxide, or carbonate), which increases farm operating costs when high alkalinity concentrations are maintained; however, alkalinity must not be so low that it interferes with nitrification or pH stability. For these reasons, a study was designed to evaluate the effects of alkalinity on biofilter performance, and CO2 stripping during cascade aeration, within two replicate semi-commercial scale Atlantic salmon smolt RAS operated with moving bed biological filters. Alkalinity treatments of nominal 10, 70, and 200 mg/L as CaCO3 were maintained using a pH controller and chemical dosing pumps supplying sodium bicarbonate (NaHCO3). Each of the three treatments was replicated three times in each RAS. Both RAS were operated at each treatment level for 2 weeks; water quality sampling was conducted at the end of the second week. A constant feeding of 23 kg/day/RAS was provided every 1–2 h, and continuous lighting, which minimized diurnal fluctuations in water quality. RAS hydraulic retention time and water temperature were 4.3 days and 12.5 ± 0.5 °C, respectively, typical of smolt production RAS in Norway.It was found that a low nominal alkalinity (10 mg/L as CaCO3) led to a significantly higher steady-state TAN concentration, compared to when 70 or 200 mg/L alkalinity was used. The mean areal nitrification rate was higher at the lowest alkalinity; however, the mean TAN removal efficiency across the MBBR was not significantly affected by alkalinity treatment. The CO2 stripping efficiency showed only a tendency towards higher efficiency at the lowest alkalinity. In contrast, the relative fraction of total inorganic carbon that was removed from the RAS during CO2 stripping was much higher at a low alkalinity (10 mg/L) compared to the higher alkalinities (70 and 200 mg/L as CaCO3). Despite this, when calculating the total loss of inorganic carbon from RAS, it was found that the daily loss was about equal at 10, and 70 mg/L, whereas it was highest at 200 mg/L alkalinity. pH recordings demonstrated that the 10 mg/L alkalinity treatment resulted in the lowest system pH, the largest increase in [H+] across the fish culture tanks, as well as giving little response time in case of alkalinity dosing malfunction. Rapid pH changes under the relatively acidic conditions at 10 mg/L alkalinity may ultimately create fish health issues due to e.g. CO2 or if aluminium or other metals are present. In conclusion, Atlantic salmon smolt producers using soft water make-up sources should aim for 70 mg/L alkalinity considering the relatively low loss of inorganic carbon compared to 200 mg/L alkalinity, and the increased pH stability as well as reduced TAN concentration, compared to lower alkalinity concentrations. 相似文献
9.
One of the challenges that Recirculating Aquaculture Systems (RAS) are still facing is the risk that in RAS fish grow less than in flow-through systems due to the accumulation of substances originating from feed, fish or bacteria associated with the water re-use. The present study investigated whether RAS with high and low accumulation levels of these substances affect feed intake and growth of Nile tilapia Oreochromis niloticus, African catfish Clarias gariepinus, and European eel Anguilla Anguilla. One-hundred and twenty individuals of each species were used (start body weights: Nile tilapia 264.8 ± 8.3 g; African catfish 253.2 ± 2.1 g and European eel 66.6 ± 1.3 g). For a period of 39 days, growth and feed intake were compared between high and low accumulation RAS. HIGH accumulation RAS was designed for maximal accumulation of substances in the water by operating the system at nearly-closed conditions (30 L/kg feed/d), using mature biofilters and high feed loads; and (2) LOW accumulation RAS was designed to be a proxy for flow-through systems by operating at high water exchange rates (1500 L/kg feed/d), new biofilters and low feed load. HIGH accumulation RAS induced a reduction in feed intake (42%) and growth (83%) of Nile tilapia, as compared to systems that are a proxy for flow-through conditions. This effect was not observed in European eel and African catfish. The cause of this reduced feed intake and growth rate of Nile tilapia is still unclear and should be addressed in further studies. 相似文献
10.
Denitrification reactors have proven their functionality in commercial recirculation aquaculture systems (RAS). Nevertheless, clogging occurs due to the low hydraulic loads necessary to accomplish anoxic conditions for a successful denitrification process in RAS, which hampers the adjustment of stable working conditions within fixed bed denitrification reactors. Reactors working on the basis of activated sludge demand careful hydraulic control and/or complex configurations for sludge retention.To develop a low-maintenance denitrification reactor, an enclosed moving bed filter, driven by recirculation of the inherent, oxygen poor gas was designed. A Self cleaning Inherent gas Denitrification reactor (SID-reactor) of 0.65 m3, which offered a moving bed volume of 0.39 m3 was connected with a RAS of semi-industrial scale for pike perch (Sander lucioperca) production. This species indicates suboptimal environmental conditions (as e.g. NO3-N concentrations above approximately 68 mg l−1) by prompt reduction of the feed intake. In different experimental series, the SID-reactor was operated with denatured ethanol, methanol, acetic acid or glycerin as carbon sources and changing operational modes.Clogging was prevented by a 40 second inherent gas recirculation twice an hour, which provided continuous, maintenance free operation with marginal energy demand. With inlet (RAS) and outlet NO3-N concentrations in the range of 49 mg l−1 and 12 mg l−1, mean denitrification rates of 199 g to 235 g NO3-N per m3 moving bed volume and day were determined for all tested carbon sources. Negative effects on the feed intake of the reared pike perch were detected with all carbon sources except methanol. Changing the mode of operation to continuous circulation of the filter bed at inlet NO3-N concentrations of 26 mg l−1, the denitrification performance reached 451 g NO3-N per m3 moving bed volume and day. The SID-reactor allowed for the reduction of freshwater exchange in the pike perch RAS from 600 l to 70 l (−88%) and the sodium bicarbonate buffer from 182 g to 31 g (−83%) per kg of administered food. The easy and reliable operation of the SID-reactor could help to establish controlled denitrification as a routine purification step in RAS. 相似文献
11.
Alessandro Del&#x;Duca Dionia Evangelista Cesar Thiago Archangelo Freato Raíza dos Santos Azevedo Edmo Montes Rodrigues Paulo Csar Abreu 《Aquaculture Research》2019,50(9):2537-2544
The aim of this study was to evaluate variability of nitrifying bacterial community in the biofilm and in the water of a recirculating aquaculture systems (RAS) in a tilapia farming in order to determine if nitrification process is dependent, or not, of nitrifying bacteria abundance. Biofilm and water samples were collected periodically for 30 days and analysed with the fluorescent in situ hybridization (FISH) technique, used to quantify ammonia‐oxidizing bacteria (AOB) and nitrite‐oxidizing bacteria (NOB). Ammonia presented the peak in the first week, while the nitrite's maximum was recorded in the second week. Nitrate increased steadily, indicating nitrification activity. Total bacterial abundance in biofilm increased continuously, while in water, it did not change significantly. In the biofilm, number of AOB was high at beginning, decreased after few days and increased again following augment of ammonia. Number of NOB also showed an increase in abundance in biofilm following the increment of nitrite and nitrate. In water, AOB and NOB did not show major variability. Relative abundance of nitrifying bacteria represented more than 30% of total bacteria in biofilm at beginning of the experiment. Their contribution decreased to >3% in last days. It indicates that nitrifying bacteria are biofilm colonizers, and that their activity seems to be directly related to the concentration of nitrogen compounds. However, contribution of nitrifying bacteria did not vary much along the time. We may conclude that the biofilm‐nitrifying bacteria plays major role in nitrification process in RAS and that the activity of these organisms is dependent of their abundance in response to the concentration of nitrogen compounds. 相似文献
12.
A new physico-chemical process for ammonia removal from fresh-water recirculated aquaculture systems (RASs) is introduced. The method is based on separating NH4+ from RAS water through an ion-exchange resin, which is subsequently regenerated by simultaneous chemical desorption and indirect electrochemical ammonia oxidation. Approach advantages include (1) only slight temperature dependence and no dependence on bacterial predators and chemical toxins; (2) no startup period is required and the system can be switched on and off at will; and (3) the fish are grown in much lower bacterial concentration, making the potential for both disease and off-flavor, lower. A small pilot scale RAS was operated for 51 d for proving the concept. The system was stocked by 105 tilapia fish (initial weight 35.8 g). The fish, which were maintained at high TAN (total ammonia nitrogen) concentrations (10–23 mgN L−1) and fish density of up to 20 kg m−3, grew at a rate identical to their established growth potential. NH3(aq) concentrations in the fish tank were maintained lower than the assumed toxicity threshold (0.1 mgN L−1) by operating the pond water at low pH (6.5–6.7). The low pH resulted in efficient CO2 air stripping, and low resultant CO2(aq) concentrations (<7 mg L−1). Due to efficient solids removal, no nitrification was observed in the fish tank and measured nitrite and nitrate concentrations were very low. The system was operated successfully, first at 10% and then at 5% daily makeup water exchange rate. The normalized operational costs, calculated based on data derived from the pilot operation, amounted to 28.7 $ cent per kg fish feed. The volume of the proposed process was calculated to be ∼13 times smaller than that of a typical RAS biofilter. The results show the process to be highly feasible from both the operational and economical standpoints. 相似文献
13.
In intensive recirculating aquaculture systems (RAS) ortho-phosphate (ortho-P) is one of the main accumulating substances, but effects of chronically elevated concentrations on fish health and production performance are still unknown. Therefore 120 juvenile turbot (Psetta maxima) were exposed to ortho-P concentrations of 3 mg/L (control – C), 26 mg/L (low – LP), 52 mg/L (medium – MP) and 82 mg/L (high – HP) for 56 days and fed until satiation with a commercial diet. Health status and feed conversion ratio (FCR) were not significantly affected by treatment (p > 0.05). Specific growth rates (SGR) and daily feed intake (DFI) of C were not considered significantly different from LP, MP and HP treatments, however LP showed significant higher DFI and SGR than HP (p < 0.05). Using non-linear regression between SGR and ortho-P concentrations, 27 mg/L ortho-P was found as the optimum for turbot growth. Although not reflected in blood plasma P levels (p > 0.05) a potential aqueous P uptake might result in metabolic benefits leading to the observed growth enhancement in the LP treatment.In a second experiment 114 juvenile turbot were exposed to ortho-P concentrations of 2 mg/L (C2) and 25 mg/L (LP2) for 63 days and fed until satiation with a low P diet (4.6 g digestible-P/kg diet). Overall production performance was low due to low voluntary feed intake. Whereas the FCR was unaffected by treatment (p > 0.05), significantly higher feed intake and biomass gain were observed for LP2 compared to C2 (p < 0.05). LP2 treatment showed a trend for higher protein retention efficiency and lower whole body lipid content (p < 0.1). The dry matter, ash, Phosphorus, Calcium and protein content in whole body did not significantly vary between treatments (p > 0.05).In conclusion the accumulation of ortho-P in RAS does not negatively affect health of turbot. Elevated ortho-P seems to have slight positive effects on production performance of juvenile turbot. Further research to quantify dietary P requirements for turbot in general, as well as for turbot raised under elevated ortho-P conditions in RAS is strongly required. 相似文献
14.
The ability to consistently and cost-effectively reduce nitrate-nitrogen loads in effluent from recirculating aquaculture systems would enhance the industry's environmental stewardship and allow improved facility proximity to large markets in sensitive watersheds. Heterotrophic denitrification technologies specifically employing organic carbon found in aquaculture system waste offer a unique synergy for treatment of land-based, closed-containment production outflows. For space-efficient fluidized sand biofilters to be used as such denitrification reactors, system parameters (e.g., influent dissolved oxygen and carbon to nitrogen ratios, C:N) must be evaluated to most effectively use an endogenous carbon source. The objectives of this work were to quantify nitrate removal under a range of C:Ns and to explore the biofilter bacterial community using three replicated fluidized sand biofilters (height 3.9 m, diameter 0.31 m; fluidized sand volume plus biofilm volume of 0.206 m3) operated at a hydraulic retention time of 15 min and a hydraulic loading rate of 188 L/min m2 at The Conservation Fund Freshwater Institute in Shepherdstown, West Virginia, USA. Nitrate reduction was consistently observed during the biofilter study period (26.9 ± 0.9% removal efficiency; 402 ± 14 g NO3-N/(m3 biofilter d)) although nitrite-N and total ammonium nitrogen concentrations slightly increased (11 and 13% increases, respectively). Nitrate removal efficiency was correlated with carbonaceous oxygen demand to nitrate ratios (R2 > 0.70). Nitrate removal rates during the study period were moderately negatively correlated with influent dissolved oxygen concentration indicating it may be possible the biofilter hydraulic retention time was too short to provide optimized nitrate removal. It is reasonable to assume that the efficiency of nitrate removal across the fluidized sand biofilters could be substantially increased, as long as organic carbon was not limiting, by increasing biofilter bed depths (to 6–10 m), and thus hydraulic retention time. These findings provide a low-cost yet effective technology to remove nitrate-nitrogen from effluent waters of land-based closed-containment aquaculture systems. 相似文献
15.
Commercial production of Atlantic salmon smolts, post-smolts, and market-size fish using land-based recirculation aquaculture systems (RAS) is expanding. RAS generally provide a nutrient-rich environment in which nitrate accumulates as an end-product of nitrification. An 8-month study was conducted to compare the long-term effects of “high” (99 ± 1 mg/L NO3-N) versus “low” nitrate-nitrogen (10.0 ± 0.3 mg/L NO3-N) on the health and performance of post-smolt Atlantic salmon cultured in replicate freshwater RAS. Equal numbers of salmon with an initial mean weight of 102 ± 1 g were stocked into six 9.5 m3 RAS. Three RAS were maintained with high NO3-N via continuous dosing of sodium nitrate and three RAS were maintained with low NO3-N resulting solely from nitrification. An average daily water exchange rate equivalent to 60% of the system volume limited the accumulation of water quality parameters other than nitrate. Atlantic salmon performance metrics (e.g. weight, length, condition factor, thermal growth coefficient, and feed conversion ratio) were not affected by 100 mg/L NO3-N and cumulative survival was >99% for both treatments. No important differences were noted between treatments for whole blood gas, plasma chemistry, tissue histopathology, or fin quality parameters suggesting that fish health was unaffected by nitrate concentration. Abnormal swimming behaviors indicative of stress or reduced welfare were not observed. This research suggests that nitrate-nitrogen concentrations ≤ 100 mg/L do not affect post-smolt Atlantic salmon health or performance under the described conditions. 相似文献
16.
This study investigated the effects of three microscreen mesh sizes (100, 60 and 20 μm) on water quality and rainbow trout (Oncorhynchus mykiss) performance compared to a control group without microscreens, in triplicated recirculating aquaculture systems (RAS). Operational conditions were kept constant during a 6-week period where the microscreens were manually rinsed three times a day. The effects of microscreen cleaning frequency and nitrification performance were subsequently assessed.Compared to the control group, microscreens removed particles, reduced particulate organic matter, and increased β-values. Particulate parameters reached steady-state in all treatment groups having microscreens at the end of the trial. The time to reach equilibrium seemingly increased with increasing mesh size but the three treatment groups (100, 60 and 20 μm) did not significantly differ at the end of the trial. Increased backwashing frequency over a 24-h period had no further significant effects on the parameters measured. The results demonstrated the role and importance of a microscreen, and showed that mesh size, within the range tested, is less important at long operations under constant conditions.Fish performed similarly in all treatments. Preliminary screening of trout gills did not reveal any pathological changes related to microscreen filtration and the resulting water quality. Biofilter performance was also unaffected, with 0′-order nitrification rates (k0a) being equivalent for all twelve systems (0.148 ± 0.022 g N m−2 d−1).Mechanisms for RAS equilibrium establishment, within and between systems with different mesh sizes, are discussed. 相似文献
17.
The long term effects of moderate elevation ORP (oxidation–reduction potential) around 300–320 mV on the growth, hematological parameters and the ability of European seabass (Dicentrarchus labrax) to react against bacterial infection was studied in recirculating aquaculture systems (RASs). Two RASs, one with a moderate ozonation (RAS-O3) and a control (RAS-C) were used in this experiment. After 60 days, seabass reared in the RAS-O3 were more able to react against a Vibrio anguillarum infection. It was in spite of the fact that seabass in the RAS-O3 showed decreased feed intake, feed conversion rate, growth rate and modified hematological parameters compared with the fish in RAS-C. It is obvious that an ORP level of 300–320 mV is too high for seabass to adapt in terms of the growth performance and the hematological parameters. However the increased ORP resulted in a better ability of the fish to react against bacterial infection. Our results strongly suggest that ORP for seabass in RAS should be elevated but not exceeding 300 mV and a slightly increased and well controlled ORP level (above 240–270 mV) has a positive effect on the disease resistance of fish. For the future, molecular methods could be utilized to identify which functional groups of microbe are contributing to the ORP effect and investigate how ORP influenced fish physiology in RASs. 相似文献
18.
Germán Merino Eduardo Uribe Gaspar Soria Elisabeth von Brand 《Aquacultural Engineering》2009,40(2):95-103
Northern scallop Argopecten purpuratus aquaculture relies on an efficient all year-round larval supply. Larvae are generally produced in closed aquaculture systems (CAS) using the batch techniques with periodical water changes. For instance, survival rates are greatly variable and can range from 0 to 80% making production of scallop larvae uncertain. The main goal of this study was to determine the feasibility of rearing scallop larvae in a recirculating aquacultural system (RAS), and secondarily to compare scallop larval growth rate and time length to reach the settling stage when reared with a traditional Chilean CAS technique and in a novel RAS technique in an industrial-like approach.Several batches of larvae were cultured in CAS and RAS. Larvae were fed on Isochrysis galbana cultured in 35-L tubular photobioreactors. Growth rates were significantly different (F11,2840 = 274.66; p < 0.001). All scallop larvae cultured in CAS showed lower growth rates ranging within 4.49 and 7.30 μm day?1 and protracted period of culture until settlement (at least 10 more culture days) than those reared in RAS (growth rates between 9.56 and 13.15 μm day?1). However, final survival (from D-larvae until settlement) of larvae reared in CAS showed higher values than those values recorded for larvae cultured on RAS. Higher growth rates observed in RAS could be attributed to a reduction in daily manipulation of the animals and/or more feed availability as well as higher temperatures and a steady state conditions in water quality. Even though, the reduction in time for rearing larvae until settlement in RAS was high, the comparison between systems is more significant in view of the reduction in make up seawater from 100% of system volume (CAS) to less than 10% of system volume (RAS). Therefore, RAS was independent from daily water quality variation from natural seawater by increasing water retention time, and with that improve water quality steady state conditions. Results of this research show that a more efficient use of water and heating systems than generally used in the Chilean hatchery industry is achievable. This is an important result since it could lead to significant reductions in the cost of operating a scallop hatchery, however further work is required to accurately compare the two systems (CAS and RAS). The main result from this research is that scallop larvae can be cultivated using recirculating aquaculture systems (RAS) as a method to increase production. The information reported in this paper will be useful for the improvement of scallop larvae culture techniques under controlled conditions. 相似文献
19.
In zero-exchange superintensive culture systems, flocculated particles (bioflocs) accumulate in the water column. Consequently, some control over the concentration of these particles must be performed. The objective of this study is to evaluate the effects of three concentrations of bioflocs on microbial activity, selected water quality indicators and performance of Litopenaeus vannamei in a tank system operated with no water exchange. A 44-day study was conducted with juvenile (6.8 g) shrimp stocked in twelve 850 L tanks at a stocking density of 459 shrimp m−3. Biofloc levels were expressed as three presets of total suspended solids (TSS) concentrations, as follows: 200 mg L−1 (T200), 400–600 mg L−1 (T400–600), and 800–1000 mg L−1 (T800–1000). TSS levels were controlled by attaching a 40 L settling tank to each culture tank. Reduction of TSS to concentrations close to 200 mg L−1 decreased the time of bacterial cell residence and significantly reduced the nitrification rates in the water (P < 0.05). The tanks in the T200 treatment had a greater variability of ammonia and nitrite (P < 0.05), which led to the need to increase the C:N ratio of the organic substrate to control ammonia through its assimilation into heterotrophic bacterial biomass. But the higher production of heterotrophic bacteria in T200 (P < 0.05) increased the dissolved oxygen demand. Nitrification rates were higher (P < 0.05) in tanks with TSS concentrations above 400 mg L−1, and ammonia and nitrite were significantly lower than in the T200 tanks. We suggest that ammonia and nitrite in the T400–600 and T800–1000 tanks were controlled primarily by nitrifying bacteria, which provided higher stability of these parameters and of dissolved oxygen. Regarding shrimp performance, the reduction of TSS to levels close to 200 mg L−1 was associated with better nutritional quality of bioflocs. Nevertheless, differences in biofloc levels and nutritional quality were not sufficient to affect the weight gain by shrimp. The rate of shrimp survival and the final shrimp biomass were lower (P < 0.05) when the TSS concentrations were higher than 800 mg L−1. Analysis of the shrimps’ gills showed a higher degree of occlusion in the T800–1000 treatment (P < 0.05), which suggests that the shrimp have an intolerance to environments with a solids concentration above 800 mg L−1. Our results show that intermediate levels of bioflocs (TSS between 400 and 600 mg L−1) appear to be more suitable to superintensive culture of L. vannamei since they create factors propitious for maintaining the system’s productivity and stability 相似文献
20.
Degradation of urea,ammonia and nitrite in moving bed biofilters operated at different feed loadings
This study investigated how removal rates of urea, ammonia, and nitrite in laboratory scale moving bed biofilters were affected by long-term feed loading. To generate different loadings, five identical freshwater flow-through systems (100 l/h) with rainbow trout (Oncorhynchus mykiss) were fed increasing fixed rations of a commercial diet. The filtered effluent from each system was lead through a moving bed biofilter installed end-of-pipe. After an acclimatization period of four months, the moving bed biofilters were spiked separately with urea, ammonia and nitrite in batch mode in three successive trials to investigate degradation kinetics. Results showed that urea, in addition to ammonia and nitrite, was degraded although the substrate limited/dependent removal rate of urea (first order kinetic) was lower than that of ammonia and nitrite. Degradation of urea could be described as first order kinetics below 2.5 mg N/l. Degradation of total ammonia nitrogen (TAN) and nitrite was substrate independent (zero order kinetic) above 2 mg N/l and subsequently substrate dependent as substrate concentrations in the bulk water declined. The transition zone from zero to first order degradation was elevated with increase in long-term biofilter loading. For ammonia and nitrite, a significant increase in the zero order removal rate constants related to long-term loading were observed up to a long-term feed loading of 207 g/d, corresponding to 69 g feed/m2 filter media/d and an TAN + urea-N concentration of 2.70 mg N/l. Long-term feed loading had no obvious effect on first order removal rate constants of any of the three nitrogenous compounds. Degradation of urea resulted in generation of ammonia demonstrating that urea degradation contributes to the ongoing nitrification activity in aquaculture biofilters. For all three types of spiking (urea, ammonia and nitrite) accumulation of nitrate was observed in the moving bed biofilters, sustaining that nitrification had occurred. 相似文献