Intensive hatchery performance of Pacific white shrimp in the biofloc system under three different fertilization levels

Bacterial inorganic nitrogen control using carbon:nitrogen ratio (C:N) manipulation is a tool for aquaculture systems. The present study assessed the hatchery performance of Litopenaeus vannamei between the mysis 1 and postlarvae 5 stages in a zero-exchange biofloc system under different C:N fertilization levels (10:1, 12.5:1 and 15:1) with dextrose. Water quality, performance parameters and water microbiology were compared among treatments. The mean values of the evaluated water quality parameters were appropriate for this production stage. Fertilization with dextrose efficiently controlled ammonia levels, which did not reach the average concentrations considered toxic for the species. In the 10:1 C:N ratio treatment, the levels of ammonia started to increase early and showed significantly higher levels from the third to the last experimental day. There was no difference among groups in means of survival (>76%) and dry weight (0.26 mg) of L. vannamei production parameters and water quality were maintained without water exchange using a biofloc system supplemented with dextrose. Therefore, the use of biofloc systems without water exchange with dextrose as a carbon source in C:N ratios of 10:1, 12.5:1 and 15:1 results in both adequate production indexes and water quality during the misis 1 to post-larvae 5 hatchery phases of L. vannamei. However, the ratios of 12.5:1 and 15:1 keep lower levels of ammonia.     

以PLA、PHBV为碳源的生物絮团技术在海水养殖中的应用

本研究以聚乳酸(PLA)和3-羟基丁酸-co-3-羟基戊酸共聚(PHBV)作为外加碳源,探究在模拟海水生物絮团养殖中,高、中、低盐度下PLA与PHBV碳源释放规律以及对海水生物絮团养殖中水质、微生物多样性及其群落结构的影响.结果显示:PHBV碳源要优于PLA碳源,中盐度更有利于各种营养盐的转化,氨氮质量浓度最终保持在3...     

Evaluation of biofloc technology in pink shrimp Farfantepenaeus duorarum culture: growth performance, water quality, microorganisms profile and proximate analysis of biofloc

In a 210d experiment, the potential of biofloc technology (BFT) was evaluated for Farfantepenaeus duorarum. Water quality parameters, microorganisms profile and proximate analysis of biofloc were also assessed. BFT did not improve the growth performance in F. duorarum when compared to conventional clear-water water exchange system (final weight and survival of 13.3 g and 63.2 %; and 13.9 g and 81.4 %, respectively). Microorganism assessment suggested a higher presence of filamentous cyanobacteria followed by protozoa, nematodes and copepods. Proximate analysis of biofloc showed crude protein and crude lipid means levels of 25 and 0.6 %, respectively, and these values varied during the experiment. F. duorarum seemed to be susceptible to high stocking density and high levels of suspended solids (>15 mL L^?1).     

Effects of suspended solids in the survival and haematological parameters of pacu juveniles (Piaractus mesopotamicus) in a biofloc technology culture system

This study determined the effects of total suspended solids (TSS) on pacu (Piaractus mesopotamicus) culture in a biofloc technology (BFT) system by performing two experiments. Experiment 1 evaluated the LC50-96 h of pacu at seven TSS levels (0, 1500, 3000, 4000, 5000, 6000 and 7000 mg L^?1). Experiment 2 evaluated haematological variables (glucose, pH, haematocrit, haemoglobin, erythrocytes and haematimetric indices) in juveniles exposed to five different sublethal TSS concentrations (0, 250, 500, 750 and 1000 mg L^?1) for 5 days. Treatments below 5000 mg L^?1 did not cause mortality, and the LC50-96 h of TSS was estimated at 5477 mg L^?1. The TSS concentrations that caused mortality in pacu juveniles were extremely high and rarely maintained in culture systems. Exposure to high TSS concentrations (mainly 750 and 1000 mg L^?1) increased blood glucose, pH, heamatocrit, erythrocytes, haemoglobin values and haematimetric indices on the first day. On the fifth day, most of the evaluated parameters stabilized at different TSS concentrations. In conclusion, pacu exposed to high TSS concentrations for short periods may undergo physiological changes, and TSS concentrations below 250 mg L^?1 are recommended for its culture in a BFT system.     

Hydrology of inland brackishwater shrimp ponds in Chachoengsao, Thailand

This study focuses on a new trend in shrimp aquaculture, the development of brackishwater ponds for Penaeus monodon culture in inland freshwater areas of Thailand’s Central Plain. Water balances were calculated for ponds and reservoirs at an inland shrimp farm in Chachoengsao, Thailand, between May and July 1999. Regulated inflow and outflow were the largest water fluxes, averaging 0.94 and 0.70 cm/day. Other daily average water gains were rainfall (0.52 cm/day) and runoff (1.7 cm/day), and other water losses were evaporation (0.31 cm/day) and seepage (0.52 cm/day). Over an entire crop cycle, of average length 109 days, average water inputs were: initial pond filling (84 cm); regulated inflow (103 cm); rainfall (57 cm); and runoff (3 cm). Average outputs were: regulated outflow (76 cm); seepage (57 cm); evaporation (34 cm); and draining at harvest (87 cm). The main feature of note in the water balance is the large volume of regulated outflow. All regulated outflow and most (82%) of the pondwater drained at harvest went directly to the irrigation canal system. Such large volumes of discharge could have serious environmental implications because small inland waterways have low assimilative capacity and pond effluent is saline. Consumptive water use for 14 inland shrimp ponds and reservoirs averaged 0.83±0.14 cm/day. Consumptive water use was also measured for 11 nearby rice fields, the main land use in the regions where inland shrimp farming is proliferating. Rice paddy water use averaged 0.91±0.17 cm/day. There was no significant difference in the daily consumptive water use of shrimp ponds and rice fields, suggesting that conversion from rice farming to shrimp farming would have little net impact on water availability for irrigation.     

Water quality dynamics and shrimp (Litopenaeus vannamei) production in intensive, mesohaline culture systems with two levels of biofloc management

A dense microbial community develops in the water column of intensive, minimal-exchange production systems and is responsible for nutrient cycling. A portion of the microbial community is associated with biofloc particles, and some control over the concentration of these particles has been shown to provide production benefits. To help refine the required degree of control, this study evaluated the effects of two levels of biofloc management on water quality and shrimp (Litopenaeus vannamei) production in commercial-scale culture systems. Eight, 50 m³ raceways were randomly assigned to one of two treatments: T-LS (treatment-low solids) and T-HS (treatment-high solids), each with four replicate raceways. Settling chambers adjacent to the T-LS raceways had a volume of 1700 L with a flow rate of 20 L min⁻¹. The T-HS raceways had 760 L settling chambers with a flow rate of 10 L min⁻¹. Raceways were stocked with 250 shrimp m⁻³, with a mean individual weight of 0.72 g, and shrimp were grown for thirteen weeks. Raceways in the T-LS treatment had significantly reduced total suspended solids, volatile suspended solids, and turbidity compared to the T-HS treatment (P ≤ 0.003). The T-LS raceways also had significantly lower nitrite and nitrate concentrations, and the T-HS raceways had significantly lower ammonia and phosphate concentrations (P ≤ 0.021). With the exception of nitrate, there were no significant differences between the change in concentration of water quality parameters entering and exiting the settling chambers in the T-LS versus the T-HS treatment. Nitrate never accumulated appreciably in the T-LS raceways, possibly due to denitrification in the settling chambers, bacterial substrate limitations in the raceways, or algal nitrate assimilation. However, in the T-HS raceways nitrate did accumulate. The T-HS settling chambers returned a significantly lower nitrate concentration and significantly greater alkalinity concentration than what entered them (P ≤ 0.005), indicating that denitrification may have occurred in those chambers. There were no significant differences in shrimp survival, feed conversion ratio, or final biomass between the two treatments. However, shrimp in the T-LS treatment grew at a significantly greater rate (1.7 g wk⁻¹ vs. 1.3 g wk⁻¹) and reached a significantly greater final weight (22.1 g vs. 17.8 g) than shrimp in the T-HS treatment (P ≤ 0.020). The results of this study demonstrate engineering and management decisions that can have important implications for both water quality and shrimp production in intensive, minimal-exchange culture systems.     

Water quality control using Spirulina platensis in shrimp culture tanks

A cyanobacterium (Spirulina platensis) was co-cultured with black tiger shrimp (Penaeus monodon) for water quality control. We evaluated the effects of: (1) three S. platensis trial conditions on inorganic nitrogen concentrations at one shrimp density (S. platensis trial conditions included: absent, nonharvested and semicontinuous harvesting) and (2) two shrimp densities on inorganic nitrogen concentrations, with and without S. platensis. Semicontinuous harvesting of S. platensis at one shrimp density resulted in significantly reduced (P<0.05) inorganic nitrogen concentrations (NH₄, NO₂ and NO₃). With S. platensis absent, ammonium and nitrite concentrations ranged from 0.5 to 0.6 mg l⁻¹, while nitrate concentrations ranged from 16 to 18 mg l⁻¹ by day 44. With nonharvested S. platensis, considerable variability occurred with nitrogen concentrations. Semicontinuous harvest of S. platensis reduced nitrate to 4 mg l⁻¹, while ammonium and nitrite ranged from 0.0 to 0.15 mg l⁻¹, respectively. The factorial evaluation of shrimp density versus presence and absence of S. platensis resulted in greatly reduced nitrogenous compounds with S. platensis present regardless of shrimp density, and only moderately increased nitrogen with greater shrimp density. Without S. platensis, all nitrogen compounds were substantially elevated and shrimp survived was significantly reduced at high shrimp density.     

Prenursery of the Pacific white shrimp in a biofloc system using different artificial substrates

This study evaluated different artificial substrates during pre-nursery of Pacific white shrimp in a biofloc system. Post-larvae (PL 5–80 PL L⁻¹) were raised in 60 L tanks filled with 52 L of chlorinated seawater (35‰) and 6 L of the microalga Chaetoceros muelleri. Four treatments were performed, including control (no artificial substrate), Bidim^® (geotextile), mosquito net screen (2 mm mesh) and Needlona^® (polyester fiber). The total surface area of artificial substrate comprised 100% of the tank area (0.89 m²). PLs were fed nine times a day using commercial feed. Molasses was added in all treatments four times a day at an average carbon:nitrogen ratio of 14.7:1. The experiment was carried out until the PLs reached PL20, and during this time, water quality, survival, weight gain and survival to salinity stress were all evaluated. Water quality parameters remained within the accepted levels for shrimp rearing, with the exception of total suspended solids (TSS) in mosquito net screen and control, which had the highest values (507 ± 5.50 mg L⁻¹ and 565 ± 23.46 mg L⁻¹, respectively). Using Needlona^® as artificial substrate increased the survival rate (91 ± 11.6%) and reduced TSS (42%) when compared to the control. No significant differences were observed in final weight and survival to salinity stress. Among the different substrates, Needlona^® was the most suitable for application in Pacific white shrimp prenursery in the biofloc system, essentially because it could maintain levels of solids suspended in water without the use of clarifiers or water exchange, resulting in higher survival.     

Microbiological quality of Litopenaeus vannamei culture using conventional and biofloc systems

Shrimp farming is a fast‐expanding activity that has supported the growth in the supply of these crustaceans to consumers around the world. However, the end product is vulnerable to contamination at all stages of the process, including the rearing tanks, where current practices prioritize to raise stocking densities and the minimization of water renewal. It is thus important to evaluate the potential of these systems for the proliferation of undesirable microorganisms, which may render the product unfit for human consumption. In the present study, the presence of coagulase‐positive Staphylococcus, Salmonella spp., Vibrio spp., and total and thermotolerant coliforms was verified in biofloc tank and conventional pond systems used for the rearing of Litopenaeus vannamei in Pernambuco, Brazil, and the results were compared with the legislation regulating the marketing of fresh shrimp. Samples were collected from two biofloc tanks with a density of 375 shrimp m^?2, and two conventional ponds with 12 shrimp m^?2. None of the samples tested positive for either Salmonella spp. or coagulase‐positive Staphylococcus, which is consistent with the legislation. While no standards are defined legally for Vibrio spp. or coliforms, very low concentrations were recorded in both systems, in comparison with other studies. While some variation in bacterial contamination was observed over the rearing process, the end product of both systems was fit for human consumption. The results of the study indicate that, while the water is not renewed in the biofloc system, the development of undesirable microorganisms can be controlled, with no adverse effects for the end product.     

The quantity of artificial substrates influences the nitrogen cycle in the biofloc culture system of Litopenaeus vannamei

This study evaluated the influence of different quantities of artificial substrate on water quality and the performance of Litopenaeus vannamei in an integrated biofilm-biofloc culture system. Thus, three treatments were performed: the control, the treatment without the addition of artificial substrate; T200, the treatment with a 200 % increase in the lateral area of the tanks using artificial substrates; and T400, the treatment with a 400 % increase in the lateral area of the tanks using artificial substrates. The study was conducted in nine 800 L tanks over 60 days. The animals were stocked at an initial density of 300 shrimp.m⁻² (equivalent to 500 shrimp m^-3), with an initial weight of 1.27 g (± 0.48). Ammonia concentrations did not differ significantly between treatments (p > 0.05). Increasing the amount of substrate from 200 % to 400 % did not cause significant differences in the nitrite concentrations between these treatments. However, in the control treatment, nitrite remained high (above 20 mg.L^-1) for a long period, negatively affecting shrimp performance. Nitrate was lower in T400, indicating a more dynamic process in the nitrogen cycle when the quantity of artificial substrate increased. Weekly growth rates, final weight, survival, and productivity were higher in the treatments integrating biofilm and biofloc substrates and did not show significant differences between T200 and T400. The results demonstrate the importance of artificial substrates in enhancing the water quality in biofloc culture systems over the long term, mostly in terms of maintaining nitrite concentrations below levels toxic to L. vannamei. The performance of the shrimp and the improved water quality at the end of the study reflected the advantages provided by incorporating artificial substrates in shrimp biofloc culture.     

Effects of different dietary lipid levels and fatty acids profile in the culture of white shrimp Litopenaeus vannamei (Boone) in biofloc technology: water quality,biofloc composition,growth and health

The objective of this study was to evaluate the influence of different dietary lipid and fatty acids on the nutritional value of bioflocs used as a feed, as well as shrimp performance and health. A total of 1800 Litopenaeus vannamei juveniles (2.87 ± 0.01 g) were cultured in biofloc technology, with a density of 200 shrimp m^?2, and fed with three isoproteic experimental diets at different lipid levels (85 g kg^?1, 95 g kg^?1 and 105 g kg^?1); each treatment was performed in triplicate. After 61 days, no significant difference was observed (P > 0.05) among the water quality parameters. For the shrimp performance, significant difference was observed (P = 0.011) among the values of survival, where treatments with lower lipid levels had higher survival (92.5 ± 3.5% and 91.0 ± 2.5%). Although there are significant differences in survival, no significant differences in the total haemocytes count (THC) were observed. For other growth performance, no differences were observed (P > 0.05). A positive correlation (r = 0.75) has been observed between the dietary oleic acid and bioflocs. The bioflocs showed ‘long‐chain’ polyunsaturated fat acids (lcPUFA), especially arachidonic acid. The shrimp showed similar growth and stayed healthy at the end of the experimental period.     

Assessment of standard aeration efficiency of different aerators and its relation to the overall economics in shrimp culture

Aerators are essential for maintaining the dissolved oxygen level in shrimp culture operations. Many types of aerators are promoted as suitable for shrimp culture, but their comparative efficiencies and water circulation patterns are least understood. The aerators viz, modified paddlewheel, Scorpion jet, Venture jet, Wavesurge were evaluated to compare the standard aeration efficiency at different saline conditions with the commonly used paddle wheel. The modified paddlewheel had the highest mean aeration efficiency of 2.018 kg O₂/ kWh at 35‰, followed by the paddlewheel with 1.434 kg O₂/ kWh at 20‰ water salinity. Compared to this, the Scorpion jet and the Wavesurge have shown the highest aeration efficiency of 0.667 and 0.412 kg O₂/ kWh at 20 and 35‰ water salinities, respectively, whereas the Venture jet has given only. The aerator's performance was better at medium water salinities (20 and 35‰) than low (5‰) or high saline (50‰) conditions. In addition to aeration, the paddlewheel aerator has given the maximum water circulation speed 3 ft/sec and coverage distance of 24 m. The cost economics were derived by keeping all other expenses constant except aeration associated costs. The internal rate of returns in shrimp culture with a modified paddle wheel was 127 % compared to the commonly used paddle wheel (120 %). However, the scorpion and wavesurge aerators have shown returns of 47 % and 27 % respectively across the salinities. The selection and sizing of aerators based on the biomass and efficiency of the aeration systems can make considerable headway in decreasing the cost of production and energy use.     

Integration of substrate in biofloc based system: Effects on growth performance,water quality and immune responses in black tiger shrimp,Penaeus monodon culture

To evaluate effect of substrate integration in biofloc based system, a 52‐day growth experiment was conducted using black tiger shrimp, Penaeus monodon juveniles (3.32 ± 0.07 g). The factorial design consisted of floc, F (with or without) as first factor and substrate (bamboo mat, B; nylon mesh, N; and without substrate) as second factor. This resulted six treatments; F + B, F + N, F, B, N and a control without biofloc and substrate. Shrimps were stocked at 110 nos. m^–3 in Fibre Reinforced Plastic (FRP) tanks and, rice flour was used as carbon source in biofloc based treatments. Incorporation of nylon mesh and bamboo mat in biofloc system trapped 31.3%–38.6% and 8.5%–13.5% total suspended solids respectively and reduced bottom solid deposition. Among the substrate based groups, significantly better development of biofilm with higher microbial population noticed in F + B compared with nylon mesh. Similarly, significantly higher final growth (p < 0.01) was recorded in F + B system followed by F + N while no significant difference in body weight recorded among floc, F or substrate based groups (B, N). Biofloc and substrate integration (F + B and F + N) resulted significantly (p < 0.01) lower feed conversion ratio compared to control and floc. Incoporation of bamboo substrate in biofloc, (F + B) improved shrimp immune responses through higher hemocyte counts and prophenoloxidase activity compared to other treatments. The study revealed that integration of substrate in the biofloc system improved growth performance, FCR and immune parameters in shrimp by trapping the suspended biofloc particles, better water quality parameters, enhanced biofilm growth and provision of quality natural food.     

小球藻与芽孢杆菌对对虾养殖水质调控作用的研究

通过在凡纳滨对虾养殖水体中添加小球藻和芽孢杆菌,研究其对养殖水质的调控作用。结果表明,小球藻和芽孢杆菌联合处理组对水质的调控效果优于只添加芽孢杆菌组或小球藻组。菌-藻联合处理组能很好地降低水体中氮、磷的含量,对氨氮的作用尤为明显;实验进行的第5天内,NH4 -N含量显著低于对照组(P<0·05),降低率为32·94%,NO2--N降低率为10·29%,PO34--P降低率为36·02%。小球藻 芽孢杆菌组NH4 -N含量平均为0·277mg/L,日均积累速率0·0135mg/L·d,而对照组为0·0472mg/L·d;NO2--N平均含量为0·334mg/L,日均积累速率为0·0617mg/L·d。小球藻在调控水质的同时也向水体释放有机物,从而引起水体COD的上升。     

The use of probiotics during the nursery rearing of the pink shrimp Farfantepenaeus brasiliensis (Latreille, 1817) in a zero exchange system

The present work evaluated the use of probiotics during the nursery rearing of the pink shrimp Farfantepenaeus brasiliensis, in a zero exchange aerobic heterotrophic culture system during 30 days. Three replicate tanks were randomly assigned to the following treatments: (1) Bacillus spp. mixture (Sanolife Pro‐‐W^®), (2) Bacillus sp., Enterococcus sp., Lactobacillus spp. mixture (Biomin Start‐grow^®), (3) Bacillus cereus var. toyoi and (4) control treatment (without probiotic addition). Bacteriological analysis monitored the abundance of presumptive Vibrio spp. in the water of experimental tanks. For the immunological analysis, shrimp haemolymph was collected to determine the granular haemocyte count and total protein concentration. Results showed that mean final weight and specific growth rate of shrimp in the probiotic treatments were significantly higher. Furthermore, shrimp reared in the probiotic treatments showed higher levels of total protein and granular haemocyte. The bacteriological analysis showed that the concentration of Vibrio spp. measured in probiotic treatment tanks was lower than that recorded in the control tanks.     

Dietary biofloc supplementation in black tiger shrimp,Penaeus monodon: effects on immunity,antioxidant and metabolic enzyme activities

A 60‐day indoor experiment was conducted to study the effect of dietary supplementation of biofloc on metabolic enzyme activities and immune responses in Penaeus monodon juveniles. Biofloc developed in indoor fibreglass‐reinforced plastic (FRP) tanks (1000 L) was used as dietary supplement in P. monodon (2.90 ± 0.10 g) reared in 1000‐L FRP tanks. Graded level of dried biofloc was included in shrimp basal diets, 0% (control, B0), 4% (B4), 8% (B8) and 12% (B12). The level of metabolic enzymes like malate dehydrogenase (MDH), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) was not significantly different with control up to 8% dietary supplementation. A higher level of total haemocyte count (THC) was noticed in B8 (22.16 ± 2.17 × 10⁶ cells mL^?1) and B4 (21.11 ± 0.56 × 10⁶ cells mL^?1) compared with control, C (14.61 ± 2.74 × 10⁶ cells mL^?1). Biofloc‐supplemented groups recorded significantly higher (P < 0.05) serum SOD and catalase activity (P < 0.01) in comparison with control. The groups fed with 4% dietary biofloc supplement recorded highest relative percentage survival (RPS), 45% after challenge with Vibrio harveyi followed by 36% and 27% RPS in B8 and B12 groups. Based on these results, it can be concluded that supplementation of biofloc even at 4% level in the feed improves immune responses and metabolic activities in black tiger shrimp juveniles.     

Effluent and production impacts of flow-through aquaculture operations in West Virginia

In light of recent changes to federal regulatory requirements placed on the aquaculture industry, aquaculture operators must act proactively to maximize their production to meet demands, compete with new operations, and maintain compliance with effluent standards. As a result, water quality characterization was conducted at six anonymous facilities using flow-through design, rearing mostly rainbow trout (Oncorhynchus mykiss) that were selected based on various water sources, operation, size, and effluent treatment.

Average concentrations and mass loadings of regulated parameters were within regulatory limits and increased in direct proportion to the mass of fish reared. However, when comparing effluent pollutant concentrations and loads with West Virginia National Pollutant Discharge Elimination System (NPDES) permit limitations, the potential for increased production existed at each facility. Based on the current West Virginia NPDES limit of 30 mg/L for total suspended solids (TSS), each facility could increase production from 147 to 819%. However, with a more stringent TSS limitation of 5 mg/L net used in states in the western US, two facilities would have to reduce production from 37 to 44%, while the other sites could increase production from 19 to 170%. Consequently, the opportunity to increase production under any set of regulatory constraints was a function of annual fish production, legal requirements, and the implementation of effective effluent treatment processes.     

Assessment and prediction of water quality in shrimp culture using signal processing techniques

In recent years, artificial intelligence methods have proved appropriate for the treatment of environmental problems. This paper presents a novel work for the assessment and prediction of water quality in shrimp aquaculture based on environmental pattern processing. Water quality studies are based on analyzing negative concentrations of compounds in shrimp ponds that inhibit good growth and reproduction of organisms. The physical–chemical variables are classified based on the negative ecological impact using the Gamma (Γ) classifier, which calculates the frequency and deviation of the measurements from a specific level. A fuzzy inference system processes the level classifications using a reasoning process that determines when a specific concentration is good or harmful for the organism and provides a water quality index, which describes the condition of the ecosystem: excellent, good, regular, and poor. An autoregressive model (AR) predicts a section of an environmental signal using historical information, and the set of predicted variables are assessed in order to estimate future water quality conditions in the system. This methodology emerges as a suitable and alternative tool to be used in developing effective water management plans.     

Dietary protein level and C/N ratio manipulation in zero‐exchange culture of Litopenaeus vannamei: Evaluation of inorganic nitrogen control,biofloc composition and shrimp performance

A 30‐day experiment was conducted to evaluate inorganic nitrogen control, biofloc composition and shrimp performance in zero‐exchange culture tanks for juvenile L. vannamei offered a 35% (P35) or 25% (P25) crude protein feed, each feed supplemented with additional carbohydrate to increase the C/N ratio to 20:1 (CN20) or 15:1 (CN15). Sucrose was used as a carbohydrate to manipulate the two C/N ratios based on the carbon and nitrogen content of both the feeds and sucrose. The four treatments were referred to as: P35 + CN20, P35 + CN15, P25 + CN20 and P25 + CN15. Each treatment consisted of four replicate tanks (125 L), each stocked with 28 shrimp (equivalent to 224 shrimp m^?3). Bioflocs formed and developed based on initial inoculation in all four treatments; and monitored water quality parameters were maintained within acceptable ranges for shrimp culture throughout the experiment. No significant effects (P > 0.05) of dietary protein level, C/N ratio or their interaction were observed on biofloc development (BFV, TSS and BFVI) and inorganic nitrogen (TAN, NO₂^?‐N and NO₃^?‐N) concentrations. At the end of the experiment, proximate analysis of the bioflocs collected from the four treatments showed crude protein levels of 21.3% ~ 32.1%, crude lipid levels of 1.6% ~ 2.8% and ash levels of 43.4% ~ 61.4%. Extracellular protease and amylase activities of the bioflocs were 9.9 ~ 14.4 U g^?1 TSS and 293.5 ~ 403.8 U g^?1 TSS respectively. Biofloc composition and enzyme activity were both affected by dietary protein level (P < 0.01) and C/N ratio (P < 0.05). Survival, per cent weight gain and protein efficiency ratio of shrimp were not affected (P > 0.05) by dietary protein level, C/N ratio or their interaction; however, the feed conversion ratios were significantly lower (P < 0.05) in treatments with high dietary protein (P35) compared with those in treatments with low dietary protein (P25). The results from this study demonstrate that dietary protein level and C/N ratio manipulation can have important implications for water quality, biofloc composition and shrimp performance in intensive, zero‐exchange biofloc‐based culture systems.     

Quality of brackish aquaculture sludge and its suitability for anaerobic digestion and methane production in an upflow anaerobic sludge blanket (UASB) reactor

Intensive recirculating aquaculture systems (RAS) produce high volumes of biosolid waste. The high salinity of brackish/marine sludge limits its use in landfill sites and waste outflows and it is a source of pollution. A reduction in sludge mass would therefore minimize the potential environmental hazard and economic burden stemming from its disposal. The aims of the current study were: 1) to characterize brackish aquaculture sludge (BAS) from three RAS in order to test for potentially suitable treatments, and 2) to test the BAS's suitability for anaerobic digestion in an upflow anaerobic sludge blanket reactor (UASB). Brackish sludge from three intensive RAS was collected periodically and analyzed for a variety of physical and chemical parameters. The mean sludge electrical conductivity and pH values ranged from 4.0 to 8.6 mS cm^− 1 and 7.0 to 7.7, respectively. A low sludge redox potential averaging − 80 mV and dissolved oxygen concentrations of less than 1 mg l^− 1 indicated the existence of anaerobic conditions. Volatile solids comprised 56 to 76% of the dry weight and the sludge volume index ranged from 44 to 69 ml g ^− 1. High concentrations of total nitrogen and total carbon were also observed, resulting in a C:N ratio ranging between 8.1 and 10.3. Toxic and/or inhibitory compounds for methanogenesis such as nitrites, nitrates and sulfides were almost absent. Sludge BOD₅ ranged from 10 to 30% dry weight. These data suggest that BAS may be used in anaerobic digestion and methanogenesis without pretreatment. This concept was tested by digesting aquaculture sludge in UASB reactors. Despite the high sulfate and phosphate concentrations in the BAS, these were found not to be inhibitory to methanogenesis. Up to 70% sludge-mass reduction and an average of 40% methane production were demonstrated.