Mathematical model for goldfish recirculating aquaculture system (GRAS)

A mathematical model is framed for a goldfish recirculating aquaculture system based on unsteady-state mass balance for prediction of the concentration of total ammonia nitrogen (TAN), nitrite-nitrogen (NO₂-N), nitrate-nitrogen (NO₃-N), dissolved oxygen (DO) and total suspended solids (TSS). The goldfish were stocked at 100 numbers per m³ of rearing water volume of 5 m³ tank capacity in the years 2009 and 2010 and the model was calibrated and validated. The recirculation flow rate was fixed at 29,000 L/day. The model parameters were estimated as k_TAN (mg of TAN generated per kg of feed): 20,000, M (mortality rate): 0.002 day⁻¹, α (percentage of feed conversion to suspended solids): 23.8, k_oxy (mg of oxygen required for fish respiration per kg of feed applied in unit time): 300,000, k_b (partial nitrification in the culture tank): 0.86 and the reaction rate constants, k₁ and k₂: 84.65 day⁻¹ and 42.03 day⁻¹ respectively and temperature growth coefficient (TGC): 5.00 × 10^-5. The model efficacy was adjudged by estimation of the coefficient of determination (R²), root mean square error (RMSE), Nash-Sutcliffe modelling efficiency (E_NS) and graphical plots between predicted and observed values.     

Effect of dietary DP/DE ratio on apparent digestibility, growth and nitrogen and phosphorus retention in rainbow trout, Oncorhynchus Mykiss (Walbaum)

The effect of DP/DE ratio in diets for rainbow trout, Oncorhynchus mykiss (Walbaum), was investigated. To evaluate growth and body composition, groups of trout were fed three experimental diets with a constant level of gross energy (25.4 ± 0.12 MJ kg^?1 dry matter (DM)) and different digestible protein/digestible energy (DP/DE) ratios (diet A, 16. 35; diet B, 17.21; dietC, 18.23 g Mr^?1). Fat, protein and energy digestibility coefficients were not affected by the DP/DE ratio of the diets. Growth and feed utilization improved markedly as dietary DP/DE ratio increased (P < .01). The efficiency of fat, protein and energy utilization tended to increase with increasing DP/DE ratio of the diets. Nitrogen discharge in effluent water per kg of weight gain was not affected by dietary treatments (mean values for: diet A, 29.9; diet B, 29.8; diet C, 29.1 g N kg^?1 weight gain) while phosphorus discharge in effluent water fell using diets with a higher DP/DE ratio (mean values for: diet A, 7.3; diet B, 6.7; diet C, 5.9 g P kg^?1 weight gain).     

Waste and particle management in a commercial, partially recirculating trout farm

The present case study, deals with a recently built aquaculture facility using 80–120 L s⁻¹ spring water for trout production. The farm consists of six raceways, discharging in a common outflow channel, leading to a drum filter equipped with 80 μm gauze. About 120 L s⁻¹ of the microscreen effluent is pumped back in the inflow channel of the six raceways. The remaining effluent is oxygenated with pure oxygen in gravity oxygenation units and led to two U-shaped raceways. The farm effluent is finally filtered by a drum filter with 63 μm mesh size. The microscreen backwash sludge is treated in a cone settler, where the sediments are extracted for agricultural manure application. The sedimentation supernatant is further led in a sub surface flow (SSF) constructed wetland prior to discharge.Due to the advanced effluent treatment within the farm, the total farm effect on the receiving effluent is kept to a minimum. The nutrient increase produced by the farm is only 0.03 mg L⁻¹ total phosphorous (TP), 1.09 mg L⁻¹ biological oxygen demand (BOD₅) and, 0.57 mg L⁻¹ total suspended solids (TSS) in the brook. Especially the incorporation of an intermediate microscreen prior to water recirculation, prevents leaching of dissolved nutrients from particulate matter, as large particles are effectively and as fast as possible removed from the water flow.At the pumping station, needed for water recirculation, the particle size distribution (PSD) was monitored with the previous microscreen in use and by-passed. When the screen was by-passed a significant crushing effect on PSD through pumping action was found. Through the removal of large particles, the crushing effect of the pumping station on the particles is prevented, as revealed by particle size distribution (PSD) measurement. Thus, leaching of dissolved nutrients is prevented twice.In consequence, the farm configuration can be recommended as an effective possibility for intensive trout production at sites with a small freshwater source and stringent effluent thresholds, even with the unexpected low treatment efficiencies measured for the microscreens. Both drum filters showed relative low treatment efficiencies of 33–53% for total suspended solids, respectively, while an efficiency of 70% should be expected from the measured PSD. With this impact, the farm still emitted a low nutrient amount, especially due to the highly effective offline microscreen backwash sludge treatment, where the SSF wetland efficiently reduced dissolved and particulate nutrients as nitrite (NO₂-N), nitrate (NO₃-N) and TSS. Thus this SSF wetland application might be suitable as a denitrification step in a closed recirculating trout farm.     

Denitrifying bioreactor inflow manifold design for treatment of aquacultural wastewater

Recirculating aquaculture systems (RAS) facilities subject to point-source effluent regulations need to implement cost-effective N remediation for their wastewater outflows. Relatively low-cost denitrifying “woodchip” bioreactors can effectively remove N from aquaculture effluents for at least one year, but questions remain about bioreactor lifespan for aquacultural wastewaters. Four pilot-scale bioreactors (L × W × D; 3.8 × 0.76 × 0.76 m), two with a conventional single distribution inflow manifold and two with an experimental multiple-header, feed-forward distribution manifold, were operated over 784 d to observe second-year N removal performance and to determine if the manifold design can influence bioreactor effectiveness. The study also quantified performance metrics for chemical oxygen demand, total suspended solids, and phosphorus. Manifold style did not have notable impact on bioreactor performance when treating wastewater under the facilities’ normal operating conditions, but the multiple distribution style demonstrated an 11 % increase in nitrate and 12 % increase in total suspended solids removal efficiency over the single distribution manifold toward the end of the study when bioreactors treated higher strength wastewater. Additionally, bioreactor performance in both manifold designs decreased from an average of 92 % total suspended solids removal efficiency under normal operating conditions to <76 % when treating the high-strength wastewater. The bioreactors provided N removal rates of 17−25 g NO₃-N m⁻³ d⁻¹ during the second year of study, demonstrating woodchip bioreactors can effectively treat aquaculture effluent for at least two years without major detrimental impacts due to clogging.     

Waste excretion of marble goby (Oxyeleotris marmorata Bleeker) fed with different diets

Marble goby (Oxyeleotris marmorata Bleeker), with its high demand and price, has a great potential as a profitable commercial aquaculture candidate in Malaysia and Southeast Asia region. Efforts are being made to produce this species in a better controlled culture environment like recirculating aquaculture system (RAS) due to poor growth performance and disease problems shown by conventional cage and outdoor pond culture systems. Quantification of waste excreted by fish is critical to RAS design. This study was conducted to characterize the waste excretion rates of marble goby fed with different diets (live food and minced fish). Ammonia-N (TAN), urea-N, nitrite-N (NO₂-N), nitrate-N (NO₃-N), total-N (TN), organic-N (ON), feces-N, 5-day biochemical oxygen demand (BOD₅) and total suspended solid (TSS) produced from marble goby were determined over a 72-h excretion period. Under given experimental conditions, the results showed that feed type had significant influence on the waste excretion rates, with marble goby fed live tilapia (Oreochromis niloticus) exhibiting significantly (P < 0.05) the lowest amount of waste excretion comparable to that of fish fed live common carp (Cyprinus carpio) and minced scads (Decapterus russellii). This indicates that feeding marble goby with tilapia poses less adverse effects on water quality and is thus a suitable diet for this species. The waste excreted by the fish is composed of nitrogenous excretion (TAN, Urea-N, ON, Feces-N), and productions of dissolved biodegradable organic substances (BOD₅) and TSS (TSS_feces + TSS_water). About 58-71% of the nitrogen consumed in food was excreted and its rate depended mainly on the feed type. TAN was the chief end-product of protein metabolism; about 74-84% of the daily total nitrogenous excretion was TAN. Urea-N accounted for 13-21% of the daily total nitrogenous excretion indicating that urea-N is an important nitrogenous excretory end-product in marble goby. The waste excretion data presented in this study can be served as a pre-requisite for designing a RAS for this species. The overall BOD₅ and TSS production found in this study also point to the need for including bio-filtration unit and suspended solids removal mechanism in the RAS design.     

The efficiency and condition of oysters and macroalgae used as biological filters of shrimp pond effluent

Current shrimp pond management practices generally result in elevated concentrations of nutrients, suspended solids, bacteria and phytoplankton compared with the influent water. Concerns about adverse environmental impacts caused by discharging pond effluent directly into adjacent waterways have prompted the search for cost‐effective methods of effluent treatment. One potential method of effluent treatment is the use of ponds or raceways stocked with plants or animals that act as natural biofilters by removing waste nutrients. In addition to improving effluent water quality prior to discharge, the use of natural biofilters provides a method for capturing otherwise wasted nutrients. This study examined the potential of the native oyster, Saccostrea commercialis (Iredale and Roughley) and macroalgae, Gracilaria edulis (Gmelin) Silva to improve effluent water quality from a commercial Penaeus japonicus (Bate) shrimp farm. A system of raceways was constructed to permit recirculation of the effluent through the oysters to maximize the filtration of bacteria, phytoplankton and total suspended solids. A series of experiments was conducted to test the ability of oysters and macroalgae to improve effluent water quality in a flow‐through system compared with a recirculating system. In the flow‐through system, oysters reduced the concentration of bacteria to 35% of the initial concentration, chlorophyll a to 39%, total particulates (2.28–35.2 µm) to 29%, total nitrogen to 66% and total phosphorus to 56%. Under the recirculating flow regime, the ability of the oysters to improve water quality was significantly enhanced. After four circuits, total bacterial numbers were reduced to 12%, chlorophyll a to 4%, and total suspended solids to 16%. Efforts to increase biofiltration by adding additional layers of oyster trays and macroalgae‐filled mesh bags resulted in fouling of the lower layers causing the death of oysters and senescence of macroalgae. Supplementary laboratory experiments were designed to examine the effects of high effluent concentrations of suspended particulates on the growth and condition of oysters and macroalgae. The results demonstrated that high concentrations of particulates inhibited growth and reduced the condition of oysters and macroalgae. Allowing the effluent to settle before biofiltration improved growth and reduced signs of stress in the oysters and macroalgae. A settling time of 6 h reduced particulates to a level that prevented fouling of the oysters and macroalgae.     

Effect of Dietary Protein Concentration on Nitrogenous Waste in Intensively Fed Catfish Ponds

Channel catfish were fed five diets containing 24, 28, 32, 36 or 40% protein in intensively stocked earthen ponds over a 141 d growing season. Mean standing crop at harvest was 7,559 kg/ha, and maximum daily feed allowance was 105 kg/ha. Dietary protein concentration had a negative linear effect on weight gain. Total ammonia-nitrogen (TAN) in pond water increased linearly as dietary protein concentration increased and was positively correlated with total protein fed. However, unionized ammonia-nitrogen (NH₃-N) was not influenced by dietary protein concentration. Dietary protein had a positive linear effect on nitrite-nitrogen (NO₁^-_- -N) concentration, which was positively correlated with total protein fed and TAN. There was no significant correlation between NO₂^-_--N and fish weight gain, although there was a significant positive correlation between NO₂^-_- -N/Cl-molar ratio in pond water and concentration of methemoglobin in the fish. Results from this study indicate that when the feeding rate is as high as 100 kg/ha/d, or 3,000 kg protein/ha/season, dietary protein concentrations of 36% and above can result in harmful concentrations of NO₂^-_--N when Cl concentration in the ponds is 2–3 mg/L. Although the NO₂^-_--N/Cl- ratio in the ponds increased to harmful levels with protein concentration of the diets, this might not be the major cause of the reduction in fish growth rate as dietary protein increased because the greatest difference in weight gain occurred at the lower protein concentrations and the greatest difference in NO₂^-_--N occurred at the higher dietary protein concentrations.     

Chlorinated secondary domestic sewage effluent as a fertilizer for marine aquaculture: I. Tilapia culture

The suitability of chlorinated secondary domestic sewage effluent as a fertilizer for culturing tilapia in seawater ponds was investigated. The only food source was the increased in situ algal production and the associated fauna and flora that were derived from the added sewage nutrients. The effluent quality was monitored, i.e., pH, NH₄N, NO₃N, ortho-P, chemical oxygen demand, suspended solids and residual chlorine. Each monitored parameter and its possible effect on the culture system is discussed.The added effluent was found to provide a suitable and inexpensive fertilizer source with projected fish yields of between 3.9 and 8.1 t ha⁻¹ per growth season of 210–226 days, depending on conditions.     

Performance and sensory evaluation of silver perch (Bidyanus bidyanus Mitchell) fed soybean or meat meal-based diets in earthen ponds

The performance of silver perch fed a commercially available diet based on meat meal (38%), grain legumes (18%), oilseeds (10%), wheat millrun (20%), fishmeal (5%) and fish oil (3%) was compared with experimental diets based on alternative protein sources in two experiments. In Experiment 1, two experimental diets contained similar contents of fishmeal and fish oil as the commercially available reference diet, but soybean (25%) and wheat millrun (>31%) were used to reduce animal protein meals by approximately 50%. The digestible protein and digestible energy of the two experimental diets was either slightly lower (31.5% and 12.8 MJ kg^?1) or slightly higher (34.9% and 14.3 MJ kg^?1) than the reference diet (32.1% and 13.2 MJ kg^?1). In Experiment 2, the two experimental diets contained no fishmeal but included higher amounts of rendered animal meals (41–48%). One of the diets had similar digestible protein to the reference diet (32%) while the other had only 25% digestible protein. Silver perch (38 g for Experiment 1 and 59 g for Experiment 2) were stocked into each of nine 0.1 ha earthen ponds with fish in three ponds fed each diet for 191 days (Experiment 1) or 187 days (Experiment 2). Survival was >94% in all ponds in both experiments. In Experiment 1, growth rates and feed conversion ratios (FCRs) ranged from 2.1 to 2.4 g fish^?1 day^?1 and 1.7 to 1.9 respectively. Growth rates were significantly (P<0.05) lower for fish fed the experimental diet with the lowest digestible energy content. Growth rates for fish fed the other experimental diet and the reference diet were similar (P>0.05). In Experiment 2, growth rates and FCRs ranged from 2.3 to 2.4 g fish^?1 day^?1 and 1.6 to 1.7. There were no significant differences in fish performance indices for any of the three diets although experimental power was low (power=0.31). A blind consumer sensory evaluation (taste panel) of fish fed the three diets in Experiment 2 rated fish as ‘highly acceptable’. The diet with the lowest digestible protein content produced the best fish in terms of ‘smell liking’, ‘flavour liking’, ‘muddy flavour strength’ and ‘fresh flavour strength’. These results confirm that soybean meal and/or rendered animal protein ingredients including meat meal and poultry offal meal, and wheat can form the basis for high‐performance, low‐cost diets for intensive pond culture of silver perch.     

室内集约化养虾池以低频率运转水处理系统调控水质效果及氮磷收支

采用低频率运转循环水处理系统(含粗滤器、臭氧仪、气液混合器,蛋白分离器、暗沉淀池等)联用池内设施(微泡曝气增氧机与净水网)开展凡纳滨对虾室内集约化养殖实验。研究了养虾池以水处理系统调控水质效果及氮磷收支。结果表明,养虾水经系统处理后,NO₂-N(53.4%～64.5%)、COD_Mn(53.4%～94.4%)与TAN(31.6%～40.4%)被显著去除,有效改进虾池水质;养殖周期内未换水与用药,虾池主要水化指标均控制在对虾生长安全范围,7号实验池(100 d)与8号对照池(80 d)主要水化指标变化范围:DO分别为 5.07～6.70 mg/L和4.38～6.94 mg/L,TAN 0.248～0.561 mg/L和0.301～0.794 mg/L,NO₂-N 0.019～0.311 mg/L和0.012～0.210 mg/L,COD_Mn 10.88～21.22 mg/L和11.65～23.34 mg/L。7号池对虾生长指数优于8号池(80 d虾病暴发终止),单位水体产量分别为1.398 kg/m²与0.803 kg/m²。氮磷收支估算结果:7号与8号池饲料氮磷分别占总收入:氮93.70%与92.37%,磷98.77%与99.09%;初始水层与虾苗含氮共占总收入6.30%与7.63%,磷共占1.23%与0.91%。总水层(含排污水)氮磷分别占总输出:氮56.45%与59.86%,磷53.26%与55.79%;收获虾体氮磷分别占总输出:氮37.07%与31.94%,磷21.37%与13.11%。7号池饲料转化率较高;池水渗漏与吸附等共损失氮磷分别占总输出:氮7.00%与9.34%,磷25.37%与31.10%。实验结果表明,虾池以低频率运转循环水处理系统联用池内设施可有效控制水质与虾病,具较高饲料转化率。     

Estimating digestible protein requirements of silver perch, Bidyanus bidyanus Mitchell

In this study, we estimated requirements for digestible protein, using intact protein sources, at one digestible energy content. Using digestibility data for silver perch (Bidyanus bidyanus Mitchell) for a large number of ingredients, we formulated a ‘summit’ diet to contain between 1.4 and 1.8 times the ‘expected requirements’ for digestible essential amino acids (based on requirements for channel catfish, Ictalurus punctatus Rafinesque). A ‘diluent’ diet was formulated to contain 0.4–0.5 times the expected requirements of digestible essential amino acids. Both ‘summit’ and ‘diluent’ diets contained similar digestible energy (14.7 MJ digestible energy kg^?1 for the summit and 13.4 MJ digestible energy kg^?1 for the diluent). Six diets were prepared with the following amounts of summit–diluent diets: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. A practical diet widely used by commercial farmers was also included as a control. Ten juvenile fish (2.1–2.6 g) were stocked into each experimental 70‐L acrylic aquarium, and each dietary treatment was randomly assigned to five replicate aquaria. Fish were fed twice daily to apparent satiation for 54 days. Final individual fish weight ranged from 4–15.5 g. Results were analysed using intersecting linear regression analysis. The optimum digestible dietary protein for diets with 13.4–14.7 MJ digestible energy kg^?1, after which protein deposition did not increase significantly, was 28%. Although this study did not determine requirements for individual amino acids, for diets with the digestible energy content used here, requirements for individual amino acids obviously did not exceed the content in the 28% protein diet. These contents are useful as an estimate of ‘recommended levels’ for silver perch diets with 13.4–14.7 MJ digestible energy kg^?1. The proximate composition of fish was affected by diet. Whole body protein and moisture increased, whereas lipid content decreased with increasing dietary protein content (and increasing protein–energy ratio and decreasing lipid). Fish size was also affected by diet; however, the changes in whole carcass proximate composition also occurred for fish fed diets 60:40, 80:20 and the summit diet which were a similar final weight.     

Effect of Dietary Ginseng Herb (Ginsana® G115) Supplementation on Growth, Feed Utilization, and Hematological Indices of Nile Tilapia, Oreochromis niloticus (L.), Fingerlings

The present study was conducted to evaluate the effect of dietary ginseng herb (Ginsana^® G115) supplementation on growth performance, feed utilization, and hematological indices of Nile tilapia, Oreochromis niloticus (L.), fingerlings. A total of 378 Nile tilapia fingerlings with an average body weight of 24.4 ± 0.2 g were divided in the six experimental treatments (three replicates each). The experiment was conducted for 17 wk. Six isonitrogenous, 27.2% digestible protein and isocaloric, 12.3 MJ/kg digestible energy experimental diets were formulated. The control diet had no Ginsana G115 added. Diets 2–6 each contained Ginsana G115 at levels of 50, 100, 150, 200, and 250 mg/kg, respectively. Growth performance and feed utilization efficiency of Nile tilapia were significantly (P ≤ 0.05) higher in all treatments receiving Ginsana G115‐supplemented diets than the control diet. Red blood cells counts, hematocrit, and hemoglobin significantly (P ≤ 0.05) increased with increasing dietary Ginsana G115 levels compared to those of the control diet. The same trend was observed for total plasma protein and total plasma globulin levels. The results of present study suggested that Nile tilapia fingerlings fed diets containing at least 200 mg/kg Ginsana G115 for 17 wk had enhanced growth performance, diet utilization efficiency, and hematological indices.     

Nutritional assessment of Australian canola meals. I. Evaluation of canola oil extraction method and meal processing conditions on the digestible value of canola meals fed to the red seabream (Pagrus auratus, Paulin)

This study assessed the nutrient and energy digestibility of a variety of canola protein products that were produced by processing canola meal under different conditions, using the red seabream, Pagrus auratus. The test canola protein products included solvent‐extracted canola meal, expeller‐extracted canola meal alone or subjected to one of two different heat treatments (120 or 150°C for 30 min), and expeller meal further processed to produce a canola protein concentrate (CPC). Solvent‐extracted soybean meal was also included in the study as a reference ingredient. Daily feed intake and blood thyroid hormone levels over the experimental period were also examined. The total digestible protein content of the expeller‐ and solvent‐extracted canola meals was 356 and 358 g per kg dry matter (g kg DM^?1) respectively. The total digestible energy content of the expeller‐ and solvent‐extracted canola meals was 14.23 and 8.60 MJ kg^?1 respectively. The organic matter digestibilities of the solvent‐extracted canola meal were poorer than noted for the expeller‐ and solvent‐extracted soybean meal. Notably, the two sources of canola meals used in this study (solvent and expeller meals) did not cause problems with declining feed intakes or changes to blood levels of thyroid hormones when included in the diets of the fish at a 30% level, and the diets were fed over a 3‐week period. The preparation of a CPC resulted in gains in total digestible energy, but a reduction in the amount of total digestible protein, relative to the expeller canola meal from which it was produced. However, the protein concentrating process marginally reduced the relative digestible value of the protein content. Heating expeller meal at 120 or 150°C for 30 min resulted in progressive reductions of all nutrient and energy digestibilities.     

Comparative performance of fixed-film biological filters: Application of reactor theory

Nitrification is classified as a two-step consecutive reaction where R₁ represents the rate of formation of the intermediate product NO₂-N and R₂ represents the rate of formation of the final product NO₃-N. The relative rates of R₁ and R₂ are influenced by reactor type characterized hydraulically as plug-flow, plug-flow with dispersion and mixed-flow. We develop substrate conversion models for fixed-film biofilters operating in the first-order kinetic regime based on application of chemical reactor theory. Reactor type, inlet conditions and the biofilm kinetic constants K_i (h⁻¹) are used to predict changes in NH₄-N, NO₂-N, NO₃-N and BOD_5. The inhibiting effects of the latter on R₁ and R₂ were established based on the γ relation, e.g.:

where BOD_5,max is the concentration that causes nitrification to cease and N is a variable relating K_i to increasing BOD₅. Conversion models were incorporated in spreadsheet programs that provided steady-state concentrations of nitrogen and BOD₅ at several points in a recirculating aquaculture system operating with input values for fish feed rate, reactor volume, microscreen performance, make-up and recirculating flow rates. When rate constants are standardized, spreadsheet use demonstrates plug-flow reactors provide higher rates of R₁ and R₂ than mixed-flow reactors thereby reducing volume requirements for target concentrations of NH₄-N and NO₂-N. The benefit provided by the plug-flow reactor varies with hydraulic residence time t as well as the effective vessel dispersion number, D/μL. Both reactor types are capable of providing net increases in NO₂-N during treatment but the rate of decrease in the mixed-flow case falls well behind that predicted for plug-flow operation. We show the potential for a positive net change in NO₂-N increases with decreases in the dimensionless ratios K_2,(R2)/K_1,(R1) and [NO₂-N]/[NH₄-N] and when the product K_1,(R1)t provides low to moderate NH₄-N conversions. Maintaining high levels of the latter reduces the effective reactor utilization rate (%) defined here as (RN_avg/RN_max)100 where RN_avg is the mean reactive nitrogen concentration ([NH₄-N] + [NO₂-N]) within the reactor, and RN_max represents the feed concentration of the same. Low utilization rates provide a hedge against unexpected increases in substrate loading and reduce water pumping requirements but force use of elevated reactor volumes. Further γ effects on R₁ and R₂ can be reduced through use of a tanks-in-series versus a single mixed-flow reactor configuration and by improving the solids removal efficiency of microscreen treatment.     

The growth of disk abalone, Haliotis discus hannai at different culture densities in a pilot-scale recirculating aquaculture system with a baffled culture tank

The growth rate of disk abalone, Haliotis discus hannai, energy consumption and changes in water quality were monitored in a pilot-scale recirculating aquaculture system (RAS) for 155 days. Baffles were installed in the RAS culture tanks to enlarge the attachment area and clean out solid waste materials automatically by hydraulic force only. The experimental disk abalones, of shell length 24.5 ± 0.5 mm, were cultured at three stocking densities, 700, 1300 and 1910 individuals/m² bottom area, in triplicate. The abalones were fed with sea mustard, Undaria pinnatifida, once a week. The abalone feed conversion rates and daily growth rates ranged from 24.5 to 25.9 and 0.32 to 0.36%, respectively. Their daily shell increments and survival rates ranged from 67.7 to 78.6 μm/day and 87.6–92.2%, respectively. The growth in weight tended to decrease at a culture density of 1300 individuals/m² bottom area, while shell increments and survival rates were acceptable at this density. The total power consumption for heating was 1185.4 kW, comprising 30.2% of the total power consumption, while the average water exchange rate was only 2.9% per day. The total ammonia nitrogen stabilized below 0.07 mg/L, after conditioning of the biofilter. The NO₂⁻–N, NO₃⁻–N and total suspended solid concentrations were also maintained within acceptable ranges for the normal growth of disk abalone. The use of the RAS with these newly designed culture tanks for disk abalone culture produced 1300 individuals/m² bottom area with a water exchange rate of only 2.9% per day and used about one-tenth of the heat energy of a conventional flow-through system.     

Dietary protein requirement of juvenile marbled spinefoot rabbitfish Siganus rivulatus

Rabbitfish are an Indo‐Pacific herbivorous marine fish that have good market demand and are suitable for aquaculture. The present work was performed to determine dietary protein inclusion necessary for optimal growth of juvenile rabbitfish Siganus rivulatus. Six diets with increasing levels of protein (10, 20, 30, 40, 50 and 60 g crude protein 100 g^?1 feed) and similar levels of gross energy (20 MJ kg^?1) were prepared and offered to S. rivulatus juveniles maintained in triplicate cages placed in two large water tanks for 49 days. Growth progressively improved with dietary protein for fish offered diets from 10% to 40% protein inclusion. Diets with greater protein levels did not improve fish growth beyond that observed in the 40% group. Daily feed intake, apparent protein utilization and feed conversion ratio decreased as dietary protein increased. Protein efficiency (PE) was greatest (1.47) in fish offered the 10% protein diet and least in fish offered the 60% protein diet (0.80). No differences in PE were observed among all other treatments (20–50%). Results of the present work suggest that minimum dietary requirement for suitable growth of S. rivulatus juveniles is 40% protein when digestible energy of the diet is 16–18 MJ kg^?1.     

Nutritive value of partially dehulled and extruded sunflower meal for post-smolt Atlantic salmon (Salmo salar L.) in sea water

This study determined the digestibility of protein in partially dehulled sunflower meal (SFM) and then, as the main goal, the nutritive value of high‐temperature extruded (≤149°C) partially dehulled SFM (SFM_EX) for post‐smolt Atlantic salmon Salmo salar in sea water. The digestibility study was conducted using the settling column approach (‘Guelph system’) for faeces collection as described by Hajen, Higgs, Beames and Dosanjh. In the nutritive value study, triplicate groups of 50 salmon (mean weight ～116 g) in 4000‐L outdoor fibreglass tanks supplied with 25–40 L min^?1, filtered, oxygenated (dissolved oxygen, 7.0–8.5 mg L^?1), 11–12°C sea water (salinity, 29–31 g L^?1), were fed twice daily to satiation one of five steam‐pelleted dry diets that contained 422 g of digestible protein (DP) kg^?1 and ～16.4 MJ of digestible energy (DE) kg^?1 on a dry weight basis for 84 days. Low‐temperature‐dried anchovy meal (LT‐AM) comprised 68.2% of the basal diet protein whereas in four test diets, SFM_EX progressively replaced up to 33.0% of the DP provided by LT‐AM in the basal diet (SFM_EX≤271 g kg^?1 of dry matter). Sunflower meal had 87.9% DP. Diet treatment did not significantly affect specific growth rate (1.39–1.45% day^?1), feed efficiency (1.19–1.26), percentage of dietary protein retained (45.8–47.5), gross energy utilization (46.5–49.4%), per cent survival (96.0–99.3) or terminal whole body and muscle proximate compositions. We conclude that SFM_EX can comprise ≥271 g kg^?1 of the dry diet or ≥22.7% of the digestible dietary protein of post‐smolt Atlantic salmon in seawater without any adverse effects on their performance.     

Discharge management in fresh and brackish water RAS: Combined phosphorus removal by organic flocculants and nitrogen removal in woodchip reactors

The current study combined P and N removal using organic flocculant chemicals and woodchip bioreactors in both freshwater and brackish water (7 ppm) recirculating aquaculture systems (RAS). The use of carbon (C) containing flocculant chemicals in the process was hypothesized to further stimulate C-demanding N removal (denitrification) in bioreactors. The trial of combined P and N removal consisted of four treatments: freshwater and brackish water RAS with and without the addition of supernatant from flocculation process to the woodchip reactor. Duplicate woodchip reactors were used per treatment and the trial was run for six weeks. 56% and 49% of P was removed from fresh and brackish sludge water, respectively. The nitrate-N (NO₃-N) removal rate was improved in the treatment when supernatant from flocculation process was used together with RAS discharge water when compared against the control. In brackish water RAS, the improvement was more pronounced (from 6.6–16.5 g NO₃-N m⁻³ d^-1) than in freshwater RAS (from 5.1–6.5 NO₃-N m⁻³ d^-1). In the freshwater bioreactors using supernatant, N was largely discharged as a nitrite-N (NO₂-N). High NO₂-N concentrations in freshwater reactors allude to incomplete denitrification reactions taking place. The results suggest that the organic flocculants did provide an additional C source for denitrification, which improved the N-removal process. However, in freshwater RAS this might have been partly due to untargeted processes such as DNRA (dissimilatory nitrate reduction to ammonium), and/or insufficient denitrification reactions taking place (excessive NO₂-N production).     

Using Chlorella vulgaris and iron oxide nanoparticles in a designed bioreactor for aquaculture effluents purification

Aquaculture operations produce high volumes of wastewater containing suspended solids and nutrients such as phosphorus and nitrogen. Treatment of water effluent from fish production ponds is essential for sustain environment. So, the present study was conducted to evaluate simultaneous use of microalgae and iron oxide nanoparticles (NPs) to purify aquaculture effluents within a designed bioreactor. For designing experiment, effluent samples were collected from fish farms in Sari, Iran. Iron oxide nanoparticles were prepared from Iranian Nano Pishgaman Company. Chlorella vulgaris was captured from the environment, then purified and cultured in the laboratory. After that, NP and microalgae were transferred to the reactor space. TSS (total suspended solid), TDS (total dissolved solid), BOD (biological oxygen demand), pH (power of hydrogen), EC (electrical conductivity), NO₃ (nitrates), NO₂ (nitrite), NH₄, (ammonium) and PO₄ (phosphates) were measured during the experiment period which NH₄ (93.67 %), NO₃ (92.23 %), NO₂ (89.3 %), and PO₄ (89.25 %) showed the highest reduction percentage, respectively. Also, significant differences among the calculated parameters (except for pH) were observed during the experiment (P < 0.05). Based on the obtained results, it is concluded that the simultaneous use of microalgae and nanoparticles is desirable for purification of aquaculture wastewaters.     

Apparent digestibility of common feed ingredients by juvenile haddock, Melanogrammus aeglefinus L.

The digestible energy (DE) content and the apparent digestibility coefficients (ADCs) of nutrients in common feed ingredients available in Atlantic Canada for haddock, Melanogrammus aeglefinus, feed formulations were determined. Juvenile haddock (mean weight, 93.9±2.1 g) were held in tanks equipped with fecal collection columns and fed practical fish meal‐based diets for 5 weeks. The experimental diets consisted of a reference diet and six test diets, each containing 30% test ingredient, with all diets being supplemented with chromic oxide (Cr₂O₃, 5 g kg^?1) as the inert digestion indicator. Three marine fish by‐products, herring meal (HM), shrimp meal (SM) and crab meal (CRM) and three plant protein supplements, dehulled soybean meal (SBM), canola meal (CAM) and corn gluten meal (CGM) were the test ingredients. The DE content of HM, SBM, CGM, CRM, CAM and SM were 18.3, 18.0, 17.8, 12.4, 10.9 and 8.8 MJ kg^?1 respectively. Protein ADCs were 95.9%, 92.2%, 92.3%, 82.0%, 83.0% and 73.5% respectively. Organic matter ADCs were 95.9%, 89.0%, 72.6%, 68.9%, 58.9% and 54.9% respectively. Lipid ADCs were 97.9%, 83.0%, 57.4%, 62.0%, 87.2% and 55.8% respectively. Based upon its high crude protein content and nutrient ADC and DE content, properly processed dehulled SBM was found to be a good plant protein supplement to partially replace HM in haddock feeds.