Freshwater Aquarium Research Articles

The efficacy of MS-222 as anaesthetic agent in four freshwater aquarium fish species

Summary The efficacy of anaesthetic tricaine methanesulfonate (MS-222) was evaluated in four freshwater aquarium fish species, Zebrafish (Danio rerio), Guppy (Poecilia reticulata), Discu (Symphysodon discus) and Green swordtail (Xiphophorus helleri). The correct dose of anaesthetic should induce the plane 4 of anaesthesia in less than 180 s, recovery in less than 300 s and must survive when exposed during 30 min to anaesthetic. Fishes were exposed to six concentrations of anaesthetic (75, 100, 125, 150, 200 and 250 mg L−1) and the time of fish reaching plane 4 of anaesthesia, post exposure recovery, and the percentage of survival when fish were subject to 30 min in the anaesthetic were recorded. The optimal doses varied according to the species: D. rerio – 75, 100 and 125 mg L−1, P. reticulata – 125, 150 and 200 mg L−1, S. discus – 75 and 100 mg L−1 and X. helleri – 125 and 150 mg L−1. The induction time generally decreased significantly with increasing concentration of MS-222 for all of the species evaluated. The recovery time had a tendency to increase with the increase of the MS-222 concentration for D. rerio, P. reticulata and S. discus. On the other hand, X. helleri recovery time decreased with the increase of MS-222 concentration. MS-222 proved to be effective in anaesthesia for all the freshwater ornamental species studied. The main results clearly show that the optimal dose to anesthetize is fish species dependent and it is completely wrong to extrapolate optimal anaesthetic concentrations between different species.

The Health Risk from Drinking Spring and Bottled Artesian Water of Central Russia

Indicators of quality and safety, as well as the useful properties of spring water, artesian bottled water and water from a municipal water supply systems are assessed. All the investigated samples of bottled drinking well water satisfy regulatory requirements for defined quality parameters. Biotesting analysis of the samples of water using two test organisms: crustacean Daphnia Magna and freshwater aquarium fish Poecillia Reticulata Peters confirmed the presence of different pollutants in spring water. Risks of oral use of investigated water are calculated. In terms of the quality of groundwater for the study area is characterized by Russian acceptable level of risk, which indicates a moderate anthropogenic pressure on ecosystems and the environment.

Morphological and genetic evidence for multiple evolutionary distinct lineages in the endangered and commercially exploited red lined torpedo barbs endemic to the Western Ghats of India.

Red lined torpedo barbs (RLTBs) (Cyprinidae: Puntius) endemic to the Western Ghats Hotspot of India, are popular and highly priced freshwater aquarium fishes. Two decades of indiscriminate exploitation for the pet trade, restricted range, fragmented populations and continuing decline in quality of habitats has resulted in their ‘Endangered’ listing. Here, we tested whether the isolated RLTB populations demonstrated considerable variation qualifying to be considered as distinct conservation targets. Multivariate morphometric analysis using 24 size-adjusted characters delineated all allopatric populations. Similarly, the species-tree highlighted a phylogeny with 12 distinct RLTB lineages corresponding to each of the different riverine populations. However, coalescence-based methods using mitochondrial DNA markers identified only eight evolutionarily distinct lineages. Divergence time analysis points to recent separation of the populations, owing to the geographical isolation, more than 5 million years ago, after the lineages were split into two ancestral stocks in the Paleocene, on north and south of a major geographical gap in the Western Ghats. Our results revealing the existence of eight evolutionarily distinct RLTB lineages calls for the re-determination of conservation targets for these cryptic and endangered taxa.

Uncovering an obscure trade: Threatened freshwater fishes and the aquarium pet markets

While the collection of fish for the aquarium pet trade has been flagged as a major threat to wild populations, this link is tenuous for the unregulated wild collection of endemic species because of the lack of quantitative data. In this paper, we examine the extent and magnitude of collection and trade of endemic and threatened freshwater fishes from India for the pet markets, and discuss their conservation implications. Using data on aquarium fishes exported from India, we try to understand nature of the trade in terms of species composition, volume, exit points, and importing countries. Most trade in India is carried out under a generic label of “live aquarium fish”; yet despite this fact, we extracted export data for at least thirty endemic species that are listed as threatened in the IUCN Red List. Of the 1.5million individual threatened freshwater fish exported, the major share was contributed by three species; Botia striata (Endangered), Carinotetraodon travancoricus (Vulnerable) and the Red Lined Torpedo Barbs (a species complex primarily consisting of Puntius denisonii and Puntius chalakkudiensis, both ‘Endangered’). Using the endangered Red Lined Torpedo Barbs as a case study, we demonstrate how existing local regulations on aquarium fish collections and trade are poorly enforced, and are of little conservation value. In spite of the fact that several threatened and conservation concern species are routinely exported, India has yet to frame national legislation on freshwater aquarium trade. Our analysis of the trade in wild caught freshwater fishes from two global biodiversity hotspots provides a first assessment of the trade in endangered and threatened species. We suggest that the unmanaged collections of these endemic species could be a much more severe threat to freshwater biodiversity than hitherto recognized, and present realistic options for management.

Parvalbumin characteristics in the sonic muscle of a freshwater ornamental grunting toadfish (Allenbatrachus grunniens)

The grunting toadfish, Allenbatrachus grunniens, is an ornamental fish in freshwater aquariums, and it has the ability to produce sounds. The sonic muscle of the toadfish is the fastest vertebrate muscle ever measured, and the rates of Ca(2+) transport and cross-bridge dissociation are also the fastest. Parvalbumins (PAs) are Ca(2+)-binding proteins that help in muscle relaxation in vertebrates. Several PA isoforms have been identified in variable ratios in different muscle types. Both male and female grunting toadfish have intrinsic sonic muscles attached to their swim bladders, but no significant difference in morphology between male and female sonic muscles has been observed. In this study, we used SDS-PAGE and western blotting to characterize the total PA expression and to identify the PAs from the sonic muscle and the white body muscle of A. grunniens. Although the total PA concentrations were similar in sonic and white muscles, there were differences in the isoform percentages. Two and four PA isoforms were identified from sonic muscle and white muscle, respectively. The estimated sizes of PA1, PA2, and PA3 in the sonic muscle of the grunting toadfish were 10, 10.5, and 10.5 kDa, respectively, and the isoelectric points of PA1, PA2, and PA3 in the grunting toadfish were 4.77, 4.58, and 4.42, respectively. In the sonic muscle, the primary PA isoform was PA1, which comprised more than 94 % of total PA, whereas PA2 comprised only 5 % of the total PA content. In contrast, in white muscle, the primary isoform was PA2, which comprised 58 % of the total PA. Both PA1 (with PA1a) and PA3 represented approximately 20 % of the total PA in white muscle. These results indicate that there is no positive correlation between a high PA content and the speed of muscle relaxation; however, PA1 might have the greatest effect on the relaxation of the grunting toadfish's sonic muscle.

Use of aquatic plants to create fluctuating hypoxia in an experimental environment

In freshwater systems, dissolved oxygen (DO) saturation frequently fluctuates, falling at night and rising during the day in response to respiration and photosynthesis, respectively, of aquatic biota. Low DO (hypoxia) is a common cause of fish kills in freshwater systems around the world. Laboratory studies on responses of fish to fluctuating DO are currently limited, and require techniques that produce a realistic cycle of DO depletion and replacement. Artificial DO-depletion mechanisms frequently used for hypoxia studies may underestimate the field effects of hypoxia on fish because of the lack of the naturally occurring synergistic effect of lower pH, and seldom allow fish to employ behavioural adaptations to hypoxia, such as aquatic surface respiration. We demonstrate proof-of-principle for an alternative method of creating fluctuating hypoxia in an experimental environment, using the natural rhythms of photosynthesis and respiration of aquatic plants to create realistic conditions. A range of volumes of aquatic macrophytes were used alone and in combination with fish to lower DO saturation in sealed freshwater aquaria, and achieved DO saturations as low as 1.3%. This cost-effective method can be deployed over long periods with minimal effort in comparison to traditional methods of DO reduction.

Aquarium Nitrification Revisited: Thaumarchaeota Are the Dominant Ammonia Oxidizers in Freshwater Aquarium Biofilters

Ammonia-oxidizing archaea (AOA) outnumber ammonia-oxidizing bacteria (AOB) in many terrestrial and aquatic environments. Although nitrification is the primary function of aquarium biofilters, very few studies have investigated the microorganisms responsible for this process in aquaria. This study used quantitative real-time PCR (qPCR) to quantify the ammonia monooxygenase (amoA) and 16S rRNA genes of Bacteria and Thaumarchaeota in freshwater aquarium biofilters, in addition to assessing the diversity of AOA amoA genes by denaturing gradient gel electrophoresis (DGGE) and clone libraries. AOA were numerically dominant in 23 of 27 freshwater biofilters, and in 12 of these biofilters AOA contributed all detectable amoA genes. Eight saltwater aquaria and two commercial aquarium nitrifier supplements were included for comparison. Both thaumarchaeal and bacterial amoA genes were detected in all saltwater samples, with AOA genes outnumbering AOB genes in five of eight biofilters. Bacterial amoA genes were abundant in both supplements, but thaumarchaeal amoA and 16S rRNA genes could not be detected. For freshwater aquaria, the proportion of amoA genes from AOA relative to AOB was inversely correlated with ammonium concentration. DGGE of AOA amoA genes revealed variable diversity across samples, with nonmetric multidimensional scaling (NMDS) indicating separation of freshwater and saltwater fingerprints. Composite clone libraries of AOA amoA genes revealed distinct freshwater and saltwater clusters, as well as mixed clusters containing both freshwater and saltwater amoA gene sequences. These results reveal insight into commonplace residential biofilters and suggest that aquarium biofilters may represent valuable biofilm microcosms for future studies of AOA ecology.

Evaluation of Emamectin Benzoate for the Control of Experimentally Induced Infestations of Argulus sp. in Goldfish and Koi Carp

The effect of 0.2% emamectin benzoate (SLICE; Intervet/ Schering-Plough Animal Health, Roseland, New Jersey) administered in top-dressed, pelleted commercial fish feed was evaluated for control of freshwater Argulus sp. in goldfish Carassius auratus and koi carp, a variant of common carp Cyprinus carpio, in freshwater aquaria at 24-25 degrees C. Sixteen individually housed goldfish were each exposed to 37 Argulus. The number of fish lice attached to each fish at the start of the experiment was not determined; however, the total number of motile fish lice in each aquarium (on fish and in the water) was determined at the start and end of each experiment. Eight goldfish were fed the control diet (0 microg x kg fish biomass(-1) x d(-1)) and eight were fed the medicated diet (50 microg x kg fish biomass(-1) x d(-1)) for seven consecutive days. After treatment, fish louse infestation in controls was 20.5 +/- 1.5 (mean +/- SE) lice per fish. No Argulus were found on fish in the treated group. In a separate experiment, 10 individually housed koi were each exposed to 128 Argulus. Five koi were fed the control diet and five were fed a low-dose medicated diet (5 microg x kg fish biomass(-1) x d(-1)) for 7 d. After treatment, fish louse infestation among the controls was 14.6 +/- 3.8 lice per koi. No Argulus were found on koi in the treated group. Hence, a 7-d regimen of oral emamectin benzoate controlled experimental infestation of Argulus when administered to goldfish at 50 microg x kg fish biomass(-1) x d(-1) and to koi at 5 microg x kg fish biomass(-1) x d(-1).

Aquisphaera giovannonii gen. nov., sp. nov., a planctomycete isolated from a freshwater aquarium

As part of a study of the diversity of planctomycetes, two novel strains, designated OJF2(T) and OJF8, were isolated from the sediments of a freshwater aquarium. The organisms were chemoheterotrophic, spherical and pink-pigmented, had an optimum growth temperature of about 30-35 °C and an optimum pH for growth of around 7.5-8.5. The predominant fatty acids were C(18:1)ω9c and C(16:0). The two strains were able to assimilate several sugars and organic acids. 16S rRNA gene sequence analysis confirmed the affiliation of these organisms to the phylum 'Planctomycetes'; they showed highest similarity to the type strains of Singulisphaera acidiphila (92.4%) and Isosphaera pallida (91.9%). On the basis of physiological, biochemical and chemotaxonomic characteristics, strains OJF2(T) and OJF8 are considered to represent a novel species of a new genus of the order Planctomycetales, for which the name Aquisphaera giovannonii gen. nov., sp. nov. is proposed. The type strain of Aquisphaera giovannonii is OJF2(T) (=CECT 7510(T) =DSM 22561(T)).

E-commerce of freshwater aquarium fishes: potential disseminator of exotic species in Brazil

The availability of freshwater aquarium fish species for sale was surveyed from July 2005 to June 2006 in Brazilian electronic commerce and the Orkut website. São Paulo was the leading state regarding virtual shops, auctions on Arremate/Mercado Livre, and hobbyists on Orkut, with 52, 44 and 46%, respectively. The Southeast and South regions led the offer of pest species such as C. carpio, C. auratus and P. reticulate. Among the 207 species for sale, 14 species considered potential pests were identified, contrasting with only one page that warned about the dangers of aquarium dumping. The easy access to fish (especially the potential pest species) through e-commerce and Orkut, together with the low total price (unitary value + shipping and handling ranging from US$ 17.67 to 30.39), and fast interstate delivery (two-four days on average) confirm the widespread e-commerce accessibility and its high dispersal potential via postal services and home hobbyists trade. It is imperative to enforce the use of warnings or alert messages in e-commerce about the dangers of biological invasions.

The freshwater aquarium trade as a vector for incidental invertebrate fauna

The aquarium trade has a long history of transporting and introducing fish, plants and snails into regions where they are not native. However, other than snails, research on species carried “incidentally” rather than deliberately by this industry is lacking. I sampled invertebrates in the plankton, and from water among bottom stones, of 55 aquaria from 43 New Zealand households. I recorded 55 incidental invertebrate taxa, including copepods, ostracods, cladocerans, molluscs, mites, flatworms and nematodes. Six were known established non-indigenous species, and eight others were not previously recorded from New Zealand. Of the latter, two harpacticoid copepod species, Nitokra pietschmanni and Elaphoidella sewelli, are not native to or known from New Zealand, demonstrating the aquarium trade continues to pose an invasion risk for incidental fauna. The remaining six species were littoral/benthic rotifers with subtropical/tropical affinities; these may or may not be native, as research on this group is limited. A variety of behaviours associated with the set-up and keeping of home aquaria were recorded (e.g., fish and plants in any home were sourced from stores, wild caught, or both, and cleaning methods varied), which made prediction of “high risk” behaviours difficult. However, non-indigenous species had a greater probability of being recorded in aquaria containing aquatic plants and in those that were heated. Methods for disposal of aquarium wastes ranged from depositing washings on the lawn or garden (a low risk for invasion) to disposing of water into outdoor ponds or storm-water drains (a higher risk). It is recommended that aquarium owners be encouraged to pour aquarium wastes onto gardens or lawns—already a common method of disposal—as invasion risk will be minimised using this method.

Effects of varying levels of noise and vibration on behavioral and physiological stress responses in two species of freshwater aquarium fish: Fathead minnows (Pimephales promelas) and bluegill sunfish (Lepomis macrochirus).

Aquariums provide beautiful underwater environments for an array of fish species, but to maintain optimum water quality and aesthetically pleasing displays, a variety of mechanical systems that unintentionally produce noise, including pumps, filters, skimmers, bubblers, etc., are necessary. The objectives of this study are to measure the acoustic properties of noise in an aquarium and examine the effects of different noise levels on the stress experienced by two species of freshwater fishes: fathead minnows (Pimephales promelas), hearing specialists, and bluegill sunfish (Lepomis macrochirus), hearing generalists. We conducted a noise mapping of several fish galleries at the Shedd Aquarium using a BK 2560 SPL meter; Leq, SEL, and minimum & maximum decibel levels were measured up to 2 kHz using a DolphinEar hydrophone. We then tested the effects of four noise levels on the stress experienced by these two fish species by measuring oxygen consumption/respiration rates with Loligo respirometry chambers and co...

Observations on morphology of insufficiently known amoebae Saccamoeba wellneri Siemensma, 1987 and Saccamoeba limna Bovee, 1972 (Gymnamoebia: Hartmannellidae)

The morphology of poorly known freshwater amoebae, Saccamoeba wellneri Siemensma, 1987 and Saccamoeba limna Bovee, 1972, were investigated using living observations at light microscopic level. S. wellneri was collected from Karloveske rameno branch of the Danube River and Strkovecke jazero lake in Bratislava, Slovakia. Its locomotive form is typical with crescent-shaped and bipyramidal crystals and uroid with short wart-like papillae. S. limna was found in an indoor freshwater aquarium in Bratislava, Slovakia. The locomotive form of S. limna has broad monopodial shape and possesses typical hyaline uroid with short nonadhesive filaments. Many small bipyramidal crystals were noted. Additional data and details on the morphology of both species were described and illustrated and re-diagnoses are presented. This paper is helpful for their identification on the base of locomotive morphology, floating, and resting forms and allows distinguishing S. wellneri and S. limna from other hartmannellids at light microscopic level.

Diatoms in a freshwater aquarium tank

Diatoms in a freshwater aquarium tank

Growth and Survival of the Tiger Tail Seahorse, Hippocampus comes

Keeping fish in home aquaria is one of the most popular hobbies globally. The United States is the largest single market for aquarium fish (Walton 1994; Wood 2001). An estimated 11% of all U.S. households with pets keep fish (Tlusty 2002), a level similar to that in Australia, the UK, and probably in many other developed countries. Approximately 10% of all aquaria are believed to be marine, and primarily house tropical coral reef fish species (Sugiyama et al. 2004). Marine aquarium hobbyists, in particular, tend to be passionate about their aquaria, well informed, and interested in marine conservation (e.g., http://www.ems.org/marine_ aquarium_trade/aquarists_profile.html). It is ironic that well-intentioned hobbyists drive a large industry that may threaten wild populations of some coral reef fish species (Wood 2001). Up to 24 million coral reef fishes of over 1000 species are traded annually, and over 98% of these marine ornamentals are wild caught (Wabnitz et al. 2003). This is in stark contrast to the freshwater aquarium hobby in which less than 2% of fishes traded are wild caught (Sugiyama et al. 2004). While the freshwater aquarium hobby trade has made significant strides over the past few decades in the development of breeding techniques for most fishes in the trade, the marine aquarium hobby trade has lagged behind. Seahorses (family Syngnathidae) are a popular group of marine aquarium fishes. In the wild, they are found worldwide in a diverse range of marine habitats, including sea grass beds, coral reefs, mangroves, and estuaries (Lourie et al. 1999). The conservation status of wild seahorse populations is of concern as populations have declined precipitously in some places (Vincent 1996; http://www.iucn.org). One reason for the observed declines in wild populations is overexploitation: the global trade in seahorses was estimated to consume at least 20 million animals annually in 1996 (Vincent 1996). In addition to the aquarium trade, seahorses are also exploited for the traditional medicines and curios trades. Early evidence suggests that the supply of seahorses to the international marine aquarium trade has been affected by their recent listing on Appendix II of the Convention on the International Trade in Endangered Species (CITES) (Job, personal observation). This decision, which came into effect in 2004, requires 169 countries to withhold export permits unless extraction of the seahorses can be shown to be sustainable. As a result, the global demand for seahorses is currently high, and prices have risen. Average wholesale prices for tropical seahorses in Australia, for example, have more than doubled over the past year (Job, personal observation). Approximately five tropical seahorse species are currently cultured on a commercial scale, primarily in the United States, Australia, 1 Corresponding author: Broome Aquaculture Centre, Kimberley College of TAFE, P.O. Box 1380, Broome, WA 6725, Australia. 2 Present address: Project Seahorse, Fisheries Centre, University of British Columbia, 2204 Main Mall, Vancouver, V6T 1Z4 Canada. JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 37, No. 3 September, 2006

Effects of the freshwater aquarium trade on wild fish populations in differentially‐fished areas of the Peruvian Amazon

Base‐line data were collected to examine the possible effects of the aquarium trade on Amazon fish populations in differentially‐fished locations in the Departmento of Loreto, Peru. Fish abundance, species diversity (richness) and biomass were quantified at three locations with differential fishing pressure, including the Rio Nanay (high pressure), Rio Apayacu and Rio Arambassa (medium) and Rio Yanayacu –Pacaya‐Samiria National Reserve (low). Seining results indicated that the location with the highest fishing pressure had reduced fish abundance, species diversity and biomass compared to the other locations. A similar trend was seen using minnow traps. There was no significant difference in abundance, diversity and biomass between the medium and low fishing pressure locations. Habitat differences (pH and conductivity) among the three locations accounted for <13% of the observed variation, and thus it seemed possible that some of the decline in the Rio Nanay location could be tentatively attributed to increased fishing pressure. Although effects of pollution and habitat alteration could not be ruled out, this is one of the first studies to provide quantitative data on the effect of the freshwater aquarium trade on wild fish populations. While results suggest success in the protection of fishes for the aquarium trade in Pacaya‐Samiria National Reserve, it also may be sustainable to establish limited levels of fishing, as was found in the medium fishing pressure locations, in order to promote economic opportunities and incentives for habitat preservation for indigenous communities.

Elevated salinity selects for a less diverse ammonia-oxidizing population in aquarium biofilters

The activity and changes in the structure of the community of the ammonia-oxidizing bacteria belonging to the Betaproteobacteria were monitored in freshwater and artificial seawater biofilters for two months after inoculation with a commercial nitrifying consortium. Both in freshwater and artificial seawater, ammonium oxidation proceeded immediately after addition of the inoculum, although initial activity in artificial seawater was lower than in freshwater. Denaturing gradient gel electrophoresis of the ammonia-oxidizing bacterial community of the inoculum and the freshwater and the artificial seawater aquaria as a function of time showed that initially only one dominant ammonia-oxidizer, closely related to Nitrosomonas marina, was detectable in all the systems. The fingerprint of the ammonia-oxidizing bacterial community in the artificial seawater biofilters continued to be dominated by this single band. In the freshwater aquaria, in contrast, the composition of the ammonia-oxidizer community became more diverse after one month, with 4–7 new bands appearing in the denaturing gradient gel fingerprint. Since the inoculum is cultivated at an average salinity of 11 g l −1, it is argued that the elevated salinity selects for a less diverse ammonia-oxidizer community in the inoculum and the artificial seawater aquaria.

Zebrafish reveals different and conserved features of vertebrate neuroglobin gene structure, expression pattern, and ligand binding.

Neuroglobin has been identified as a respiratory protein that is primarily expressed in the mammalian nervous system. Here we present the first detailed analysis of neuroglobin from a non-mammalian vertebrate, the zebrafish Danio rerio. The zebrafish neuroglobin gene reveals a mammalian-type exon-intron pattern in the coding region (B12.2, E11.0, and G7.0), plus an additional 5'-non-coding exon. Similar to the mammalian neuroglobin, the zebrafish protein displays a hexacoordinate deoxy-binding scheme. Flash photolysis kinetics show the competitive binding on the millisecond timescale of external ligands and the distal histidine, resulting in an oxygen affinity of 1 torr. Western blotting, immune staining, and mRNA in situ hybridization demonstrate neuroglobin expression in the fish central nervous system and the retina but also in the gills. Neurons containing neuroglobin have a widespread distribution in the brain but are also present in the olfactory system. In the fish retina, neuroglobin is mainly present in the inner segments of the photoreceptor cells. In the gills, the chloride cells were identified to express neuroglobin. Neuroglobin appears to be associated with mitochondria-rich cell types and thus oxygen consumption rates, suggesting a myoglobin-like function of this protein in facilitated oxygen diffusion.

NUPELA EXOTICA SPECIES NOVA: UNE DIATOMÉE D'UN AQUARIUM TROPICAL D'EAU DOUCE. AVEC DES REMARQUES SUR LA BIOGÉOGRAPHIE DU GENRE / Nupela exotica sp. nov., a diatom from a tropical freshwater aquarium. With comments on the genus biogeography

A new naviculoid diatom species, Nupela exotica Monnier, Lange-Bertalot & Bertrand spec. nov., has been discovered in a tropical freshwater aquarium near Orléans (France). It is described on the basis of SEM studies, complemented by LM observations. The diatom flora and water characteristics are particular, since taxa from Europe and from tropical zones are associated. Among 54 counted taxa three belong to the recently established genus Nupela. The water of the aquarium is fairly acid, rich in nutrients and mineral content, the specific conductance is moderately high. Biogeography and ecology of N. exotica are discussed and compared with other species of the genus.

An improved system for the control of dissolved oxygen in freshwater aquaria

A system for the removal and control of dissolved oxygen (DO) from freshwater was designed and constructed with aquarium-type fish studies in mind. Degassed water was obtained using a partial vacuum of −14 psi, and DO regulated at an aquarium scale using electronically controlled aeration with timed partial water renewal. The degassing system was capable of producing water with ∼1.7 mg L −1 DO within 10 min of operation, and 0.55 mg L −1 after 2 h. The control system was capable of maintaining DO levels of ca 0.8 mg L −1 over 48 h in the absence of aeration and further capable of precisely controlling DO levels as low as 1.16±0.002 mg L −1 (mean±SEM) with aeration over a 48 h period.