Closed Aquaculture Systems Research Articles

Impacts of rearing techniques on growth, survival and bacterial microbiota of carpet shell clam (Ruditapes decussatus) larvae

In this study, we investigate the impacts of two water treatment regimes, the closed aquaculture system (CAS) and flow-through system (FTS), on the carpet shell clam (Ruditapes decussatus) larval microbiota, growth and survival. A bacteriological barrier (B) was created among breeder stage treated by florfenicol (FF, 8 mg L−1day−1 per 5 days). After spawning, larvae were maintained in five different rearing techniques: CAS; FTS; B + CAS; B + FTS and B + CAS + FF (8 mg L−1 day−1 per 3 days). Significant decrease was observed in both total bacterial count and presumptive Vibrio count (PVC) in FF-treated breeders. Besides, larvae reared in B + FTS showed significantly lower PVC than larvae maintained in other rearing techniques. It was also determined that growth and survival of larvae reared in B + CAS + FF and B + FTS were significantly better than those reared in other systems. One hundred and twelve Vibrio strains, isolated from breeders, eggs and larvae, were subjected to some bacteriological tests (API 20E strips, vibriostatic agent O/129, growth at different temperatures and salinity). Vibrio alginolyticus was the predominant isolated species (36.61 %), followed by V. fluvialis (25 %), V. vunificus (17.86 %), V. cholera (13.39 %) and V. paraheamolyticus (7.14 %). These results may contribute to the understanding of the effect of rearing techniques on the bacterial load, survival and growth of early life stages of R. decussatus larvae.

Growth Performance of Tomato Plant and Genetically Improved Farmed Tilapia in Combined Aquaponic Systems

Aquaponic system is an integration of aquaculture and hydroponics in a closed aquaculture system. Plants are able to grow without the presence of soil using natural fertilizer available in the system as a result of nutrients produced from nitrification process by the nitrifying bacteria. The aim of this study is to evaluate the growth performances of Genetically Improved Farmed Tilapia (GIFT) and tomato plant (Solanum lycopersicum) in a combined aquaponic system. This system is a mix of Deep Water Raft System (DWRS) using a styrofoam base with a small hole made for plant to float placed in a small pot filled with gravel used to support the plants and Media Filled System (MFS) applying a plant tank fully filled with gravel as media for the plant to grow. This study was conducted to determine whether combined aquaponic system could improve the effectiveness of the plant growth. GIFT gained 94% of body weight and tomato increased 96.3% in terms of plants height and started flowering (the early stage of fruit formation). Besides, the range in concentration of TAN (0.29±0.4 mg L-1), nitrite (0.65±0.59 mg L-1), nitrate (1.29±1.29 mg L-1) and phosphate (0.57±0.1 mg L-1) recorded in the culture system are suitable for facilitating the nitrification process. Analysis of the data proves that the combined aquaponic system is more effective than the single DWRS aquaponic system.

Predictive model of food intake of the Seabass Dicentrarchus labrax in closed aquaculture systems

Event Abstract Back to Event Predictive model of food intake of the Seabass Dicentrarchus labrax in closed aquaculture systems Allan T. Souza1*, Irene Martins2, José F. Gonçalves3 and Rodrigo Ozorio1 1 CIIMAR - Centro Interdisciplinar de Investigação Marinha e Ambiental, Portugal 2 IMAR - Institute of Marine Reasearch, Portugal 3 ICBAS - Instituto de Ciências Biomédicas Abel Salazar, Portugal Fish feeding is the main source of waste in aquaculture and is also responsible for most of the environmental impacts derived from this activity. The European Seabass Dicentrarchus labrax is one of the most farmed fishes in the continent, generating an important load of waste on the environment. The consumption of food in fishes is highly dependent on the water temperature and salinity, which create a source of variability on the amount of the ration consumed by fishes. This issue is often neglected by farmers, which aggravates the ration waste. The use of models in aquaculture is increasing in the recent years, and is an excellent tool to combine an increased production with the mitigation of environmental impacts. In this context, this study aimed at developing a predictive model of the D. labrax consumption rate in closed aquaculture systems. Based on the literature review we were able to develop a conceptual diagram and a prototype of the model using the STELLA software (isee®). The preliminary results indicated that the model was capable of predicting the ration consumption of the D. labrax according to the oscillations in the water temperature and salinity. The consumption rate and growth were higher at 21ºC and with a salinity of 28 psu. Laboratory assays are need to validate the models outputs, and they are scheduled to start in October 2015. Finally, the model’s structure, equations, inputs and outputs were integrated into an easy-to-use software developed by the FoodInTech® company, that will help farmers to increase their yields and reduce the waste of ration and the nutrient load on the environment. Acknowledgements This research was supported by project MODELFISH (31-03-01-FEP-0152), funded by PROMAR and co-funded by the European Fisheries Fund (EFF). This work was partially funded by AQUAIMPROV (reference NORTE-07-0124-FEDER-000038), co-financed by the North Portugal Regional Operational Programme (ON.2 - O Novo Norte), under the National Strategic Reference Framework, through the European Regional Development Fund. Keywords: Aquaculture, modelling, Modelling and simulation, piscicultura, sotware Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Poster Presentation Topic: Physiology, Behavior and Toxicology Citation: Souza AT, Martins I, Gonçalves JF and Ozorio R (2015). Predictive model of food intake of the Seabass Dicentrarchus labrax in closed aquaculture systems. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.FMARS.2015.03.00216 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: 09 Dec 2015; Published Online: 09 Dec 2015. * Correspondence: Dr. Allan T Souza, CIIMAR - Centro Interdisciplinar de Investigação Marinha e Ambiental, Porto, 4050-543, Portugal, allantsouza@gmail.com 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 Allan T Souza Irene Martins José F Gonçalves Rodrigo Ozorio Google Allan T Souza Irene Martins José F Gonçalves Rodrigo Ozorio Google Scholar Allan T Souza Irene Martins José F Gonçalves Rodrigo Ozorio PubMed Allan T Souza Irene Martins José F Gonçalves Rodrigo Ozorio 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.

Capture, transport, and husbandry of elephant sharks (Callorhinchus milii) adults, eggs, and hatchlings for research and display.

Elephant sharks (Callorhinchus milii) have the slowest evolving genome of all vertebrates and are an interesting model species for evolution research and a prized display animal. However, their deep water habitat, short breeding season, fragility, and susceptibility to stress-induced mortality have made them difficult animals to capture, keep in captivity, and obtain fertilized eggs from. Gravid females were captured by rod and reel from Western Port Bay, Australia and transferred to a 40 000 L closed aquaculture system to lay their eggs before being released. The water quality parameters, averaged over three seasons of 4-6 weeks (mean ± standard deviation) were: 16.8°C ± 2.31, salinity 37.1 ± 2.9 g/L, ammonia 0.137 ± 0.2 mg/L, nitrite levels 0.89 ± 0.9 mg/L, nitrate 66.8 ± 45.6 mg/L, pH 7.8 ± 0.18, dissolved oxygen levels 93.6 ± 5.3%, ORP 307 ± 63.3 mV. Eggs were incubated in purpose built egg cages and embryos hatched after 143.6 days ± 1.3 at 16.9 ± 0.9°C of incubation. These procedures led to no adult mortality in the last 2 years and 620 eggs with known deposition date were collected over 4 years, of which 81.5% (±4.8) were viable. Collection of abundant embryological material with known deposition date is of paramount importance for evolutionary developmental research. We attribute this success to excellent water quality, maximum reduction of stress during capture, transport, handling, and captive care.

DO Control System Based on PID Control Algorithm for Aquaculture

Improving process control in aquaculture can reduce costs and increase the effectiveness of operations. DO (dissolved oxygen) is necessary for the growth and metabolism of fish. This paper designs a system based on PID control algorithm to make real-time DO monitoring and controlling in closed aquaculture system. It can real-time monitor environmental parameters such as PH, DO, temperature, and the height of water. In addition, it can control DO in time. According to the actual changes of DO, the frequency converter automatically controls the aerator’s work. The overall structure design of the system software and hardware are introduced in detail, followed by control scheme, principle and experiment results of the system. The experiment indicates that the relative error of sensor’s measuring DO is controlled in ±1.3% and DO content variations is stabilized within ±0.4 mg/L. The system has the feature of safety control, simple circuit, low cost and high real time.

Biofilm Formation by the Fish Pathogen Flavobacterium columnare: Development and Parameters Affecting Surface Attachment

Flavobacterium columnare is a bacterial fish pathogen that affects many freshwater species worldwide. The natural reservoir of this pathogen is unknown, but its resilience in closed aquaculture systems posits biofilm as the source of contagion for farmed fish. The objectives of this study were (i) to characterize the dynamics of biofilm formation and morphology under static and flow conditions and (ii) to evaluate the effects of temperature, pH, salinity, hardness, and carbohydrates on biofilm formation. Nineteen F. columnare strains, including representatives of all of the defined genetic groups (genomovars), were compared in this study. The structure of biofilm was characterized by light microscopy, confocal laser scanning microscopy, and scanning electron microscopy. F. columnare was able to attach to and colonize inert surfaces by producing biofilm. Surface colonization started within 6 h postinoculation, and microcolonies were observed within 24 h. Extracellular polysaccharide substances and water channels were observed in mature biofilms (24 to 48 h). A similar time course was observed when F. columnare formed biofilm in microfluidic chambers under flow conditions. The virulence potential of biofilm was confirmed by cutaneous inoculation of channel catfish fingerlings with mature biofilm. Several physicochemical parameters modulate attachment to surfaces, with the largest influence being exerted by hardness, salinity, and the presence of mannose. Maintenance of hardness and salinity values within certain ranges could prevent biofilm formation by F. columnare in aquaculture systems.

An Anaerobic Slurry Module for Solids Digestion and Denitrification in Recirculating Minimal Discharge Marine Fish Culture Systems

An anaerobic denitrification module with improved stability for closed aquaculture systems is described. The module was fitted to a recirculating fish mariculture system. The 18 m3 system consisted of a fish basin, a nitrification trickling filter and the module reported here, which was composed of a stirred slurry basin and two subsequent sedimentation tanks. Commercial fish feed (pellets) introduction into the slurry basin simulated nutrient input equivalent to 450 kg of fish biomass. About 50 kg of the sea bream, Sparus aurata, were introduced to bioassay water quality. Conditions remained stable as long as the mixing remained regular (16 wk). Feeding and sampling continued for an additional 6 wk of irregular mixing, during which time water quality gradually deteriorated causing 19% mortality of the stocked fish population. The system removed a majority of the total dissolved nitrogen (N) by denitrification and total phosphorus (P) by immobilization in the sludge. The rate of denitrification approached 9 mmol N/L/d. Hydrogen sulfide concentration in the fish basin remained low. The results constitute a proof‐of‐concept for the utility and resilience of slurry basins in the control of anaerobic processes and the maintenance of good water quality in recirculating fish culture.

Effect of Increasing Salinity on Weight-Specific Filtration Rate of Juvenile ScallopArgopecten purpuratusReared at Two Temperatures: Is Any Effect Related to Ammonia Buildup?

Larvae of the northern Chilean scallop Argopecten purpuratus (Lamarck, 1819) can be produced in hatcheries in closed aquaculture systems (CAS), and then early juveniles transferred to the sea for further grow-out. A new scallop mass production method from larvae to early juveniles that applies recirculation aquaculture system (RAS) technology has been developed at Universidad Catolica del Norte. RASs might lose water by evaporation, which increases salinity. Water temperature will increase as well if it is not controlled. An experiment was performed to determine the effect of varying salinity and temperature over water quality parameters and scallop physiological processes. Feeding behavior of A. purpuratus was determined under CAS with daily water exchange for hatchery-produced juvenile scallops (mean shell height, 26.5 mm; SD, 1.9) reared at salinities of 34, 38, and 42 g/L, and temperatures at 16°C and 22°C. Weight-specific filtration rates (WFRs) were analyzed at day 12 and again at day 55. Scallops were fed Isochrysis galbana and Chaetoceros calcitrans (ratio, 1:1). Results shows that WFRs analyzed for a 24 h period had a tendency to be lower at 0 h than at 24 h, for both temperatures; WFRs were higher at 22°C than at 16°C. A significant positive regression was also found between final WFR and total ammonia nitrogen (both NH3-N and NH4 -N) levels. Results presented here should be interpreted with caution outside the shell height range of 26.5 ± 1.9 mm. These results are applicable to the management of A. purpuratus under controlled conditions, such as a RAS.

Closed Aquaculture Systems for the Mass Production of Food Fish

Closed Aquaculture Systems for the Mass Production of Food Fish

A comparison of larval production of the northern scallop, Argopecten purpuratus, in closed and recirculating culture systems

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 7.30μmday−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 13.15μmday−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.

Aquatic modules for bioregenerative life support systems based on the C.E.B.A.S. biotechnology

Most concepts for bioregenerative life support systems are based on edible higher land plants which create some problems with growth and seed generation under space conditions. Animal protein production is mostly neglected because of the tremendous waste management problems with tetrapods under reduced weightlessness. Therefore, the “Closed Equilibrated Biological Aquatic System” (C.E.B.A.S.) was developed which represents an artificial aquatic ecosystem containing aquatic organisms which are adpated at all to “near weightlessness conditions” (fishes Xiphophorus helleri, water snails Biomphalaria glabrata, ammonia oxidizing bacteria and the rootless non-gravitropic edible water plant Ceratophyllum demersum). Basically the C.E.B.A.S. consists of 4 subsystems: a ZOOLOGICASL COMPONENT (animal aquarium), a BOTANICAL COMPONENT (aquatic plant bioreactor), a MICROBIAL COMPONENT (bacteria filter) and an ELECTRONICAL COMPONENT (data acquisition and control unit). Superficially, the function principle appears simple: the plants convert light energy into chemical energy via photosynthesis thus producing biomass and oxygen. The animals and microorganisms use the oxygen for respiration and produce the carbon dioxide which is essential for plant photosynthesis. The ammonia ions excreted by the animals are converted by the bacteria to nitrite and then to nitrate ions which serve as a nitrogen source for the plants. Other essential ions derive from biological degradation of animal waste products and dead organic matter. The C.E.B.A.S. exists in 2 basic versions: the original C.E.B.A.S. with a volume of 150 liters and a self-sustaining standing time of more than 13 month and the so-called C.E.B.A.S. MINI MODULE with a volume of about 8.5 liters. In the latter there is no closed food loop by reasons of available space so that animal food has to be provided via an automated feeder. This device was flown already successfully on the STS-89 and STS-90 spaceshuttle missions and the working hypothesis was verified that aquatic organisms are nearly not affected at all by space conditions, i . e. that the plants exhibited biomass production rates identical to the ground controls and that as well the reproductive, and the immune system as the the embryonic and ontogenic development of the animals remained undisturbed. Currently the C.E.B.A.S. MINI MODLULE is prepared for a third spaceshuttle fligt (STS-107) in spring 2001. Based on the results of the space experiments a series of prototypes of aquatic food production modules for the implementation into BLSS were developed. This paper describes the scientific disposition of the STS-107 experiments and of open and closed aquaculture systems based on another aquatic plant species, the Lemnacean Wolffia arrhiza which is cultured as a vegetable in Southeastern Asia. This plant can be grown in suspension culture and several special bioreactors were developed for this purpose. W. arrhiza reproduces mainly vegetatively by buds but also sexually from time to time and is therefore especially suitable for genetic engineering, too. Therefore it was used, in addition, to optimize the C.E.B.A.S. MINI MODULE to allow experiments with a duration of 4 month in the International Space Station the basic principle of which will be explained. In the context of aquaculture systems for BLSS the continuous replacement of removed fish biomass is an essential demand. Although fish reproduction seems not to be affected in the short-term space experiments with the C.E.B.A.S. MIMI MODULE a functional and reliable hatchery for the production of siblings under reduced weightlessness is connected with some serious problems. Therefore an automated “reproduction module” for the herbivorous fish Tilapia rendalli was developed as a laboratory prototype. It is concluded that aquatic modules of different degrees of complexity can optimize the productivity of BLSS based on higher land plants and that they offer an unique opportunity for the production of animal protein in lunar or planetary bases.

Biological denitrification applied to a marine closed aquaculture system

The denitrification of marine effluents was tested using a technology involving immobilized denitrifying bacteria on granular material. To ensure efficient denitrification, an organic carbon addition was needed. The denitrification rate was quantified in the pilot-unit working as a batch fermentor. A first order kinetic model according to the nitrate nitrogen concentration was found and the rate coefficient is an increasing function of the TOC/N(NO − 3) ratio, with an optimum ratio of 1 g g −1. Smaller values led to a nitrite production which was nevertheless oxidized in the treatment line; higher values could lead to the appearance of toxic sulphides. Working on stationary hydraulic loads, the treatment capacity of the unit was about 2.4 kgN(NO − 3) m −3 j −1. It was necessary to wash the packing once every 3 days. The malfunctioning of the unit could be avoided by the oxidation-reduction potential control.

Animal protein production modules in biological life support systems: Novel combined aquaculture techniques based on the closed equilibrated biological aquatic system (C.E.B.A.S.)

Based on the experiences made with the Closed Equilibrated Biological Aquatic System (C.E.B.A.S.) which was primarily deveoloped for long-term and multi-generation experiments with aquatic animals and plants in a space station highly effective fresh water recycling modules were elaborated utilizing a combination of ammonia oxidizing bacteria filters and higher plants. These exhibit a high effectivity to eliminate phosphate and anorganic nitrogen compounds and arc. in addidition. able to contribute to the oxygen supply of the aquatic animals. The C.E.B.A.S. filter system is able to keep a closed artificial aquatic ecosystem containing teleost fishes and water snails biologically stable for several month and to eliminate waste products deriving from degraded dead fishes without a decrease of the oxygen concentration down to less than 3.5 mg/l at 25 °C. More advanced C.E.B.A.S. filter systems, the BIOCURE filters, were also developed for utilization in semiintensive and intensive aquaculture systems for fishes. In fact such combined animal-plant aquaculture systems represent highly effective productions sites for human food if proper plant and fish species are selected The present papers elucidates ways to novel aquaculture systems in which herbivorous fishes are raised by feeding them with plant biomass produced in the BIOCURE filters and presents the scheme of a modification which utilizes a plant species suitable also for human nutrition. Special attention is paid to the benefits of closed aquaculture system modules which may be integrated into bioregenerative life support systems of a higher complexity for, e. g.. lunar or planetary bases including some psychologiccal aspects of the introduction of animal protein production into plant-based life support systems. Moreover, the basic reproductive biological problems of aquatic animal breeding under reduced gravity are explained leading to a disposition of essential research programs in this context.

Preliminary estimation of tropical ornamental fish metabolite production rates

The rational design of closed aquaculture systems requires data on metabolite production rates. The metabolite of primary concern is often ammonia. Ammonia formation rates for a number of tropical ornamental fish types and sizes were determined. Cyprinus carpio, Barbus conchonius, Pseudotropheus auratus and Carassius auratus auratus were used as representative egg-layers while Xiphophorus variatus and Xiphophorus helleri represented the live-bearers. Specific metabolite production rates, R′, were determined not only in terms of mass of fish but also the amount of feed. For instance, R′ (Amm-N) for 1.33 g unit size Barbus conchonius was determined to be 155.9 mg Amm-N kg-fish −1% feed −1 day −1. In an attempt to produce a general model for all the ornamental fish investigated, all values of R′ obtained were correlated with fish sizes to produce an equation R′ (Amm-N) = 1.57-[30×log(itUW)] where UW = unit fish size.

Marine heterotrophic bacteria associated with enrichment culture of nitrifying bacteria planned for closed aquaculture systems

Ammonium and nitrite oxidizing bacteria were enriched in separate cultures using a primary inoculum of water from an enclosed shrimp rearing facility. Each enrichment was continued by transfer to increasing volumes of medium up to 151. Seventy four strains of heterotrophic bacteria were isolated; seventeen from each primary inoculum, and twenty from each of the 151 enrichments at the time when all the ammonium or nitrite had been utilized. All the isolates, described by 101 characters, were subjected to numerical taxonomy. During the enrichment for ammonium oxidizers, a strong selective pressure led to the disappearance of some strains, mostly enterobacteria. Two taxonomic groups composed of pseudomonads and asporogenous Gram positive rods were associated with the ammonium oxidizers. The population was characterized by an inability to use amino acids as carbon and energy sources. In contrast, the strains associated with nitrite oxidizers were able to use all the carbon and energy sources tested. Many of these strains were Gram positive, asporogenous aerobic rods, others were Gram negative pseudomonads.

The comparison of two simple protocols designed to initiate and stimulate ammonia oxidation in closed aquaculture systems

This study was conducted to evaluate the use of inocula of frozen cells to accelerate the conditioning of new closed seawater systems. The time required to establish nitrification was shortened by about 30% when using frozen bacteria alone or combined with organic matter (food pellets) enrichment of the seawater before inoculating. When only frozen cells were added, the ammonia concentration stayed below the LC50 of tested animals. Two batches which were not inoculated with frozen ammonia-oxidizing bacteria demonstrated the possible contribution of some heterotrophic nitrification.

Temperature Effects on the Growth of Blue Tilapia in Intensive Aquaculture

Abstract Blue tilapias (Oreochromis aureus) were grown at 20, 25, and 30°C in closed aquaculture systems to develop a growth model for flowing-water husbandry of this species. Blue tilapias required 0.69 ± 0.05 temperature units (TU) per millimeter of growth in length (mean ± 95% confidence level; 1 TU = 1°C above 17.8°C maintained for 30 d). This requirement was verified in a second experiment in which blue tilapias were grown at 28°C on feed rations calculated from anticipated growth. The daily length increment (▵L, mm) of blue tilapias grown at constant temperature (T, °C) within the range 20–30°C can be predicted from the equation ▵L = 0.048T – 0.853.

Growth of mullet (Liza ramada) fed three commercial trout and eel feeds in open and closed aquaculture systems

Summary Mullet fingerlings (Liza ramada) were fed three different commercial feeds (two types of pellet trout feed and one eel paste); growth performance was monitored for 14 weeks in an open as well as a closed intensive aquaculture system. The1 mullet fingerlings exhibited different growth and survival rates according to the various feed types. Weight increase and survival were poorer and the differences between the feeding treatments were more pronounced in the flow through system. These findings are discussed in relationship to differences in the stability of the feed and to the physical and chemical criteria in each rearing system.

Pathogen Reduction in Closed Aquaculture Systems by UV Radiation: Fact or Artifact?

Pathogen Reduction in Closed Aquaculture Systems by UV Radiation: Fact or Artifact?

Management of a closed brackish water system for high-density fish culture by biological and chemical water treatment

During a 1-year operation of a warm water recycling system (salinity about 8‰) sufficient water quality was maintained under high stocking density conditions using Tilapia and the European eel as potential candidates for intensive farming. The final fish: water ratio was 1 : 23 (or 43.5 g fish per 1 water) for the whole experimental culture unit. The total water volume of the system was about 5 m 3. The water treatment unit held 52% of the total volume, whereby 46% was available for fish culture. Combined biological (trickling filter with Hydropack-foil) and chemical (ozonation) water treatment proved to be useful to meet water quality requirements under these rearing conditions. After an initial conditioning period of the biofilter, BOD varied from 4.5 to 6.0 mg O 2/l, ammonium levels were maintained at less than 1 mg/l and nitrite concentrations averaged 1 mg/l. The average efficiency (oxidation rate) of the biofilter for NH 4 +-and NO 2 −-oxidation was 31% and 13.2%, respectively. The pH was stabilized slightly above 7.0 when a denitrification unit was connected to the system. Nitrate concentration of the system levelled of between 200 and 400 mg/l and was regulated by the addition of an electron donator (first glucose solution, then methanol) to the denitrification unit; the elimination rate averaged 50% with a maximum of 98%. High nitrite levels were avoided by ozone treatment of the recycled water. The accumulation of low-biodegradable substances was also successfully counteracted by ozonation. Fish growth rates of about 30% per month at high stocking densiteis were reached for Tilapia at a fish: water ratio of 1 : 4.6 (217 g fish per 1 water), indicating that a combination of biological water treatment and ozonation supports intensive fish culture in a closed aquaculture system.