Commercial Aquaculture Systems Research Articles

Metagenome sequencing and recovery of 444 metagenome-assembled genomes from the biofloc aquaculture system

Biofloc technology is increasingly recognised as a sustainable aquaculture method. In this technique, bioflocs are generated as microbial aggregates that play pivotal roles in assimilating toxic nitrogenous substances, thereby ensuring high water quality. Despite the crucial roles of the floc-associated bacterial (FAB) community in pathogen control and animal health, earlier microbiota studies have primarily relied on the metataxonomic approaches. Here, we employed shotgun sequencing on eight biofloc metagenomes from a commercial aquaculture system. This resulted in the generation of 106.6 Gbp, and the reconstruction of 444 metagenome-assembled genomes (MAGs). Among the recovered MAGs, 230 were high-quality (≥90% completeness, ≤5% contamination), and 214 were medium-quality (≥50% completeness, ≤10% contamination). Phylogenetic analysis unveiled Rhodobacteraceae as dominant members of the FAB community. The reported metagenomes and MAGs are crucial for elucidating the roles of diverse microorganisms and their functional genes in key processes such as nitrification, denitrification, and remineralization. This study will contribute to scientific understanding of phylogenetic diversity and metabolic capabilities of microbial taxa in aquaculture environments.

In vitro assessment of copper naphthenate against the free-living stages of Ichthyophthirius multifiliis

Ichthyophthirius multifiliis is an important freshwater teleost pathogen that often leads to significant economic losses to food and ornamental fish industry. The purpose of this study was to assess the acute toxicity of copper naphthenate to the free-living stages of I. multifiliis (theronts and protomonts). The results obtained showed that the administration of low doses (4, 6, 8, 10 mg/l) of 2.4 % copper naphthenate during a 4 h exposure killed nearly all free-living stages of I. multifiliis (theronts, protomonts). The demonstrated in vitro efficacy of copper naphthenate suggests its great potential to control I. multifiliis infections in commercial aquaculture systems.

Comparison of Different Biofilter Media During Biological Bed Maturation Using Common Carp as a Biogen Donor

This experiment analysed the operation of submerged and dripping biological filters with three types of filling: commercial fitting HXF12KLL (CF), two innovative polypropylene aggregates (PPA) and polyethylene screw caps for PET bottles (PSC). The experiment determined the time needed to reach full filter functionality at the maturation stage, the time needed to start successive stages of the nitrification process and the maximum concentration of each nitrogen compound in water in the recirculation systems. The filter operation characteristics after the maturation stage were also examined. These issues are crucial during the preparation and launch of new aquaculture facilities. A literature analysis indicated that the ability of biological filters to oxidise nitrogen compounds is affected by a number of factors. Studies conducted at various centres have covered selected aspects and factors affecting the effectiveness of biological filters. During this study, the model fish common carp (Cyprinus carpio) was used. The current experiment involved examination of biological filter maturation and operation during the carp fry rearing stage, which allowed the biofilter operation characteristics to be determined. At the third day of the experiment, the ammonium concentration reached approximately 3 mg NH4-N/dm3. It remained at this level for 10 days and later decreased below 0.25 mg NH4-N/dm3. The maximum nitrite concentration ranged from 11.7 mg/dm3 to 20.9 mg NO2-N/dm3 within 9 to 20 days and later decreased with time. Nitrate concentrations were seen to increase during the experiment. The all applied biofilter media showed possibility to be used in commercial aquaculture systems.

Exercise improves growth, alters physiological performance and gene expression in common carp (Cyprinus carpio)

It has been suggested that induced swimming has the potential to improve the growth performance of fish. We tested this hypothesis by measuring growth, metabolic efficiency and physiological capacity of common carp (Cyprinus carpio). Fish were swum at different exercise regimes: 0.0 (control), 1.5 and 2.5 body lengths per second (BL/s) in 1600 L recirculating raceways for 4 weeks. The results showed a significant increase in weight gain, specific growth rate, improved feed conversion efficiency, and a higher hepatosomatic index for 2.5 BL/s exercised fish compared to control. Glycogen, protein and lipid energy stores in hepatic and muscular tissue showed limited differences among experimental groups. Likewise, plasma [Na+], [K+] and [Cl−] remained stable at all swimming regimes. Expression of genes controlling energy metabolism and growth (IGF-I axis, cytochrome oxidase) and stress response (cortisol receptor, heat shock protein 70) revealed clear regulatory roles as the mRNA transcript levels of IGF-I and growth hormone receptors in hepatic tissue were up-regulated in fish exercised for 3–4 weeks at 2.5 BL/s. Oxygen consumption rate and swimming performance (Ucrit) for each experimental group were evaluated in parallel in Blazka-type swim-tunnels (3.9 L) and showed no training effect while prolonged swimming at 1.5 and 2.5 BL/s facilitated ammonia excretion and prevented build-up of plasma ammonia. Overall, these data suggest that sustained exercise at 2.5 BL/s enhanced growth and physiological fitness without compromising energy metabolism or ion-regulation. Our study provides a prospective of implementing exercise as a tool to increase fish production efficiency in commercial aquaculture systems.

The Inner Workings of the Outer Surface: Skin and Gill Microbiota as Indicators of Changing Gut Health in Yellowtail Kingfish.

The mucosal surfaces and associated microbiota of fish are an important primary barrier and provide the first line of defense against potential pathogens. An understanding of the skin and gill microbial assemblages and the factors which drive their composition may provide useful insights into the broad dynamics of fish host–microbial relationships, and may reveal underlying changes in health status. This is particularly pertinent to cultivated systems whereby various stressors may led to conditions (like enteritis) which impinge on productivity. As an economically important species, we assessed whether the outer-surface bacterial communities reflect a change in gut health status of cultivated Yellowtail Kingfish (Seriola lalandi). Active bacterial assemblages were surveyed from RNA extracts from swabs of the skin and gills by constructing Illumina 16S rRNA gene amplicon libraries. Proteobacteria and Bacteroidetes were predominant in both the skin and gills, with enrichment of key β-proteobacteria in the gills (Nitrosomonadales and Ferrovales). Fish exhibiting early stage chronic lymphocytic enteritis comprised markedly different global bacterial assemblages compared to those deemed healthy and exhibiting late stages of the disease. This corresponded to an overall loss of diversity and enrichment of Proteobacteria and Actinobacteria, particularly in the gills. In contrast, bacterial assemblages of fish with late stage enteritis were generally similar to those of healthy individuals, though with some distinct taxa. In conclusion, gut health status is an important factor which defines the skin and gill bacterial assemblages of fish and likely reflects changes in immune states and barrier systems during the early onset of conditions like enteritis. This study represents the first to investigate the microbiota of the outer mucosal surfaces of fish in response to underlying chronic gut enteritis, revealing potential biomarkers for assessing fish health in commercial aquaculture systems.

Effect of environmental conditions and management strategies in commercial aquaculture systems on juvenile milkfish (Chanos chanos) quantified by scale cortisol

Event Abstract Back to Event Effect of environmental conditions and management strategies in commercial aquaculture systems on juvenile milkfish (Chanos chanos) quantified by scale cortisol Inken Hanke1, 2*, Bart Ampe3, 4, Andreas Kunzmann1, Astrid Gärdes1 and Johan Aerts2, 3 1 Leibniz Centre for Tropical Marine Research (LG), Germany 2 Ghent University, Faculty of Pharmaceutical Sciences, Belgium 3 Institute for Agricultural and Fisheries Research (ILVO), Belgium 4 Institute for Agricultural and Fisheries Research (ILVO), Animal Sciences Unit, Belgium The global intensification of commercial aquaculture production has become an increasing threat for the performance and growth of cultured fish. Besides suboptimal management strategies, such as high stocking densities, fish have to cope with changing environmental conditions, as commonly encountered in outdoor systems. In a previous experimental study, we observed a significant increase in stress response mediated by the hypothalamic-pituitary-interrenal (HPI) axis and quantified by ontogenetic and regenerated scale cortisol, when exposing juvenile milkfish to a single stimulus of minute and gradual temperature increase (manuscript currently under review). In this study, we evaluated for the first time the stress response of juvenile milkfish in a commercial aquaculture setting by using ontogenetic scale cortisol. Fish were collected from four different cages, from the beginning of the mariculture park, nearby channel inlet to the open ocean (F1, F2), along the Guiguiwanen Channel in mid (F3) and the end region (F4) of the mariculture park in Bolinao (Philippines). Ontogenetic scales of 6 fish per cage/sampling point were analyzed for cortisol and environmental conditions were monitored after 86 (D86) and 100 days (D100) of culture time. For all stations, scale cortisol was significantly higher at D100. Hereby, significant differences in scale cortisol levels were observed between stations per sampling as well as in daily incorporation of scale cortisol. Highest scale cortisol levels were recorded at F4, where fish were kept at the highest stock density. On the other hand, fish from F1 exhibited the highest rate of daily incorporated scale cortisol. Subsequently, when taking into account the existing culture conditions, scale cortisol levels showed that management strategy as well as location of the cage in the mariculture park/along the channel had a significant effect on the stress level of fish. This is to our knowledge the first study on chronic stress in milkfish. Hereby, the use of scale cortisol was shown to be effective, making it a powerful tool in optimizing aquaculture systems as well as in monitoring gradual climate changes in wild stock. Keywords: Scale cortisol, stress response, Aquaculture, temperature, Milkfish Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018. Presentation Type: Oral Presentation Topic: Aquaculture Citation: Hanke I, Ampe B, Kunzmann A, Gärdes A and Aerts J (2019). Effect of environmental conditions and management strategies in commercial aquaculture systems on juvenile milkfish (Chanos chanos) quantified by scale cortisol. Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00081 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Apr 2018; Published Online: 07 Jan 2019. * Correspondence: Ms. Inken Hanke, Leibniz Centre for Tropical Marine Research (LG), Bremen, Germany, Inken.Hanke@leibniz-zmt.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Inken Hanke Bart Ampe Andreas Kunzmann Astrid Gärdes Johan Aerts Google Inken Hanke Bart Ampe Andreas Kunzmann Astrid Gärdes Johan Aerts Google Scholar Inken Hanke Bart Ampe Andreas Kunzmann Astrid Gärdes Johan Aerts PubMed Inken Hanke Bart Ampe Andreas Kunzmann Astrid Gärdes Johan Aerts Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Three Draft Genome Sequences of Vibrio coralliilyticus Strains Isolated from Bivalve Hatcheries.

ABSTRACTReported here are the genome sequences of three Vibrio coralliilyticus isolates RE87, AIC-7, and 080116A. Each strain was isolated in association with oyster larvae in commercial aquaculture systems. These draft genomes will be useful for further studies in understanding the genomic features contributing to V. coralliilyticus pathogenicity.

The denitrification characteristics of Pseudomonas stutzeri SC221-M and its application to water quality control in grass carp aquaculture.

To reduce ammonium and nitrite in aquaculture water, an isolate of the denitrifying bacterium Pseudomonas stutzeri, SC221-M, was obtained. The effects of various nitrogen and carbon sources, the ratio of carbon to nitrogen and temperature on bacterial growth, denitrification rates and the expression levels of nirS and nosZ in SC221-M were studied. The following conditions were determined to be optimal for growth and denitrification in SC221-M: NaNO2 as the nitrogen source, sodium citrate as the carbon source, a carbon to nitrogen ratio range of 4–8, and a temperature range of 20–35°C. Subsequently, SC221-M and the Bacillus cereus BSC24 strain were selected to generate microbial preparations. The results showed that addition of the microbial preparations decreased various hydrochemical parameters, including total dissolved solids, ammonium, nitrite, total nitrogen and the chemical oxygen demand. Nitrogen removal rates were highest on day 9; the removal rates of BSC24, SC221-M, a mixed preparation and a 3× mixed preparation were 24.5%, 26.6%, 53.9% and 53.4%, respectively. The mixed preparation (SC221-M+BSC24) was more effective at removing nitrogen than either the SC221-M or BSC24 preparation. Roche 454 pyrosequencing and subsequent analysis indicated that the control and other groups formed separate clusters, and the microbial community structure in the water changed significantly after the addition of microbial preparations. These results indicate that the addition of microbial preparations can improve both the water quality and microbial community structure in an experimental aquaculture system. P. stutzeri strain SC221-M and its related microbial preparations are potential candidates for the regulation of water quality in commercial aquaculture systems.

Experimental Transmission of Infectious Pancreatic Necrosis Virus from the Blue Mussel, Mytilus edulis, to Cohabitating Atlantic Salmon (Salmo salar) Smolts

Integrated multitrophic aquaculture (IMTA) reduces the environmental impacts of commercial aquaculture systems by combining the cultivation of fed species with extractive species. Shellfish play a critical role in IMTA systems by filter-feeding particulate-bound organic nutrients. As bioaccumulating organisms, shellfish may also increase disease risk on farms by serving as reservoirs for important finfish pathogens such as infectious pancreatic necrosis virus (IPNV). The ability of the blue mussel (Mytilus edulis) to bioaccumulate and transmit IPNV to naive Atlantic salmon (Salmo salar) smolts was investigated. To determine the ability of mussels to filter and accumulate viable IPNV, mussels were held in water containing log 4.6 50% tissue culture infective dose(s) (TCID50) of the West Buxton strain of IPNV ml(-1). Viable IPNV was detected in the digestive glands (DGs) of IPNV-exposed mussels as early as 2 h postexposure. The viral load in mussel DG tissue significantly increased with time and reached log 5.35 ± 0.25 TCID50 g of DG tissue(-1) after 120 h of exposure. IPNV titers never reached levels that were significantly greater than that in the water. Viable IPNV was detected in mussel feces out to 7 days postdepuration, and the virus persisted in DG tissues for at least 18 days of depuration. To determine whether IPNV can be transmitted from mussels to Atlantic salmon, IPNV-exposed mussels were cohabitated with naive Atlantic salmon smolts. Transmission of IPNV did occur from mussels to smolts at a low frequency. The results demonstrate that a nonenveloped virus, such as IPNV, can accumulate in mussels and be transferred to naive fish.

The interaction of infectious salmon anaemia virus (ISAV) with the blue mussel,Mytilus edulis

Integrated multi-trophic aquaculture (IMTA) is an alternative approach to mono-culture aquaculture that reduces environmental impacts of commercial aquaculture systems by combining the cultivation of fed species with extractive species. Shellfish play a critical role in IMTA systems by filter-feeding particulate-bound organic nutrients. They may also increase or decrease disease risk on farms by serving as reservoirs or barriers for important finfish pathogens such as infectious salmon anaemia virus (ISAV). This study aimed to optimize culture and molecular assays in shellfish tissues and to determine the fate of ISAV in mussels, Mytilus edulis. To determine detection limits, qRT-PCR and culture assays in both CHSE- and ASK cells were optimized in ISAV-inoculated mussel tissue homogenates. Both qRT-PCR and culture assays performed in ASK cells had comparable detection limits of 102.8 TCID50 mL−1. The ISAV RNA genome was consistently detected in digestive gland tissue of ISAV-exposed mussels. Viable ISAV was not detected in mussel tissues by culture analysis in CHSE- and ASK cells. The fact that qRT-PCR analysis resulted in positive cycle threshold (CT) values that corresponded to the detectable range of ISAV in ASK culture assays suggests that little to no viable ISAV particles are present in the mussel tissues.

Ingestion of Lepeophtheirus salmonis by the blue mussel Mytilus edulis

Integrated multi-trophic aquaculture (IMTA) is an exciting alternative approach to mono-culture aquaculture that reduces environmental impacts of commercial aquaculture systems by combining the cultivation of fed aquaculture species (finfish) with extractive aquaculture species (e.g., shellfish and seaweed). This increases the sustainability and profitability of finfish culture as the organic particulate wastes can be removed by the shellfish extractive component and dissolved inorganic nutrients are extracted by the seaweed component. Shellfish play a critical role in an IMTA system by extracting particulate bound organic nutrients; however they may also influence pathogen dynamics by serving as a reservoir or as a barrier for finfish pathogens, depending on pathogen physiologies. The sea louse, Lepeophtheirus salmonis, has recently made a spectacular comeback as a major parasitic pest of farmed Atlantic salmon (Salmo salar L.) in the Northeast of the United States. The re-emergence of this parasite is due to development of louse resistance to SLICE™, the drug of choice for treating L. salmonis infestations over the last decade. Incorporation of mussel crops on salmon farms may be an alternative method to reduce the infectious pressure of sea lice on farms if mussels can consume copepodids, the planktonic and infectious stage of sea lice. Our study demonstrated that mussels can remove copepodids from the water column. Individual mussels were exposed to copepodids (200 copepodids l−1) for 30- and 60-min durations. Copepodids were observed in the buccal cavity and in stomach contents. Molecular analyses confirmed the presence of copepodids in mussel stomach contents.

A molecular and multivariate approach to the microbial community of a commercial shallow raceway marine recirculation system operating with a Moving Bed Biofilter

Information on commercial aquaculture systems bacterial communities is scarce. The present study was performed in a turbot shallow raceway recirculating aquaculture system throughout 221 days after initial fish stocking. The dynamics of bacteria attached to a Moving Bed Biofilm Reactor and the distribution of the system culturable planktonic heterotrophic bacteria were assessed. Different levels of free heterotrophic bacteria were found over time: ≤2.6 × 104 CFU mL−1 in incoming and ozonated water and ≥1.5 × 106 CFU mL−1 in raceway and biofilter water. 16S rRNA gene sequencing of nine strains persistently isolated from the system affiliated with Bacteroidetes, α-Proteobacteria or γ-Proteobacteria. Polymerase chain reaction-denaturating gradient gel electrophoresis (PCR-DGGE) data showed temporal and spatial segregation of attached biofilter community. The first 32 days were the most important for bacterial establishment with higher culturable bacteria biomass loadings and higher community diversity. Multivariate canonical correspondence analysis of PCR-DGGE showed that the most common aquaculture water quality descriptors explained 70% of the DGGE pattern variability.

Comparing denitrification rates and carbon sources in commercial scale upflow denitrification biological filters in aquaculture

Aerobic biological filtration systems employing nitrifying bacteria to remediate excess ammonia and nitrite concentrations are common components of recirculating aquaculture systems (RAS). However, significant water exchange may still be necessary to reduce nitrate concentrations to acceptable levels unless denitrification systems are included in the RAS design. This study evaluated the design of a full scale denitrification reactor in a commercial culture RAS application. Four carbon sources were evaluated including methanol, acetic acid, molasses and Cerelose™, a hydrolyzed starch, to determine their applicability under commercial culture conditions and to determine if any of these carbon sources encouraged the production of two common “off-flavor” compounds, 2-methyisoborneol (MIB) or geosmin. The denitrification design consisted of a 1.89 m 3 covered conical bottom polyethylene tank containing 1.0 m 3 media through which water up-flowed at a rate of 10 lpm. A commercial aquaculture system housing 6 metric tonnes of Siberian sturgeon was used to generate nitrate through nitrification in a moving bed biological filter. All four carbon sources were able to effectively reduce nitrate to near zero concentrations from influent concentrations ranging from 11 to 57 mg/l NO 3–N, and the maximum daily denitrification rate was 670–680 g nitrogen removed/m 3 media/day, regardless of the carbon source. Although nitrite production was not a problem once the reactors achieved a constant effluent nitrate, ammonia production was a significant problem for units fed molasses and to a less extent Cerelose™. Maximum measured ammonia concentrations in the reactor effluents for methanol, vinegar, Cerelose™ and molasses were 1.62 ± 0.10, 2.83 ± 0.17, 4.55 ± 0.45 and 5.25 ± 1.26 mg/l NH 3–N, respectively. Turbidity production was significantly increased in reactors fed molasses and to a less extent Cerelose™. Concentrations of geosmin and MIB were not significantly increased in any of the denitrification reactors, regardless of carbon source. Because of its very low cost compared to the other sources tested, molasses may be an attractive carbon source for denitrification if issues of ammonia production, turbidity and foaming can be resolved.

Gill ATPase activities of silver perch, Bidyanus bidyanus (Mitchell), and golden perch, Macquaria ambigua (Richardson): Effects of environmental salt and ammonia

The Australian freshwater fish, silver and golden perch, are increasingly being used for aquaculture. Addition of salt to water is commonly used in commercial aquaculture to reduce stress attributed to high ammonia concentrations. The activities in gill homogenates of ouabain-sensitive Na +/K +-ATPase and NEM-sensitive ATPases (as a measure of H +-ATPases) of silver and golden perch were measured after maintaining the fish in water containing different salt and ammonia concentrations. Six treatments were applied in a 2 × 3 factorial design: two salt treatments, low salt (LS) of 2.5 g l − 1 and high salt (HS) 5 g l − 1 , and three ammonia treatments, no added ammonia (NA), low ammonia (LA), 3 mg total ammonia nitrogen (TAN) l − 1 and high ammonia (HA), 5 mg TAN l − 1 . In both species, activity of Na +/K +-ATPase was lowest in fish kept in the LSNA treatment (7.4 ± 0.4 μmol Pi mg protein − 1 h − 1 for silver perch and 3.1 ± 0.6 for golden perch) and highest in the HSHA treatment (15.2 ± 1.0 μmol Pi mg − 1 protein h − 1 for silver and 8.4 ± 1.2 for golden perch). In both species there was a significant increase ( P < 0.001) in Na +/K +-ATPase activity with increase in salt concentration and with an increase in ammonia concentrations. A significant interaction ( P < 0.036) between salt and ammonia on Na +/K +-ATPase activity was observed in silver but not in golden perch. In contrast, the lowest activity for NEM-sensitive ATPase was observed in the HSNA treatment (1.0 ± 0.2 μmol Pi mg − 1 protein h − 1 for silver and 1.5 ± 0.4 for golden perch) and highest in LSHA treatment (2.9 ± 0.4 μmol Pi mg − 1 protein h − 1 for silver and 3.6 ± 1.2 for golden perch). In both species there was a significant decrease in NEM-sensitive ATPase activity with increase in salt concentration and an increase in activity with increase in ammonia ( P < 0.003). In silver perch, a significant interaction between the treatments was observed ( P < 0.02). The results suggest that in these species of freshwater fish the Na +/K +-ATPase has a role in salt and ammonia homeostasis and that the NEM-sensitive ATPases are more active in fish kept in water with a lower salt content. It is possible that the increase in ammonia resistance when salt is added to the environmental water in commercial aquaculture systems may be due to the effects of salt on gill Na +/K +-ATPase activity rather than the NEM-sensitive ATPases.

Denitrification in aquaculture systems: an example of a fuzzy logic control problem

Nitrification in commercial aquaculture systems has been accomplished using many different technologies (e.g. trickling filters, fluidized beds and rotating biological contactors) but commercial aquaculture systems have been slow to adopt denitrification. Denitrification (conversion of nitrate, NO 3 − to nitrogen gas, N 2) is essential to the development of commercial, closed, recirculating aquaculture systems (<1 water turnover 100 day −1). The problems associated with manually operated denitrification systems have been incomplete denitrification (oxidation–reduction potential, ORP>−200 mV) with the production of nitrite (NO 2 −), nitric oxide (NO) and nitrous oxide (N 2O) or over-reduction (ORP<−400 mV), resulting in the production of hydrogen sulfide (H 2S). The need for an anoxic or anaerobic environment for the denitrifying bacteria can also result in lowered dissolved oxygen (DO) concentrations in the rearing tanks. These problems have now been overcome by the development of a computer automated denitrifying bioreactor specifically designed for aquaculture. The prototype bioreactor (process control version) has been in operation for 4 years and commercial versions of the bioreactor are now in continuous use; these bioreactors can be operated in either batch or continuous on-line modes, maintaining NO 3 − concentrations below 5 ppm. The bioreactor monitors DO, ORP, pH and water flow rate and controls water pump rate and carbon feed rate. A fuzzy logic-based expert system replaced the classical process control system for operation of the bioreactor, continuing to optimize denitrification rates and eliminate discharge of toxic by-products (i.e. NO 2 −, NO, N 2O or H 2S). The fuzzy logic rule base was composed of >40 fuzzy rules; it took into account the slow response time of the system. The fuzzy logic-based expert system maintained nitrate-nitrogen concentration <5 ppm while avoiding any increase in NO 2 − or H 2S concentrations.

Apparent ammonia-nitrogen production rates of white sturgeon ( acipenser transmontanus) in commercial aquaculture systems

Ammonia production rates of white sturgeon ( Acipenser transmontanus) were measured at three commercial farms in the Sacramento, California area. Mean daily ammonia-nitrogen production (RNH3) values ranged from 1.5 to 27.6 mg total ammonia-nitrogen (TAN) (kg fish) −1 h −1 for sturgeon ranging in size from 0.09 to 3.8 kg. Peak hourly average ammonia production rates were observed to occur 2–6 h after the consumption of a meal, reaching values as high as 1.4 times the mean daily values. Multiple regression analysis determined that 87% of the variations in the RNH3 values could be attributed to variations in protein ration, and the protein ration was the only variable considered which was significant in predicting the mean daily ammonia production rates.