Numerical simulation of the hydrodynamics within octagonal tanks in recirculating aquaculture systems

A three-dimensional numerical model was established to simulate the hydrodynamics within an octagonal tank of a recirculating aquaculture system. The realizable k-e turbulence model was applied to describe the flow, the discrete phase model （DPM） was applied to generate particle trajectories, and the governing equations are solved using the finite volume method. To validate this model, the numerical results were compared with data obtained from a full-scale physical model. The results show that： （1） the realizable k-e model applied for turbulence modeling describes well the flow pattern in octagonal tanks, giving an average relative error of velocities between simulated and measured values of 18% from contour maps of velocity magnitudes; （2） the DPM was applied to obtain particle trajectories and to simulate the rate of particle removal from the tank. The average relative error of the removal rates between simulated and measured values was 11%. The DPM can be used to assess the self-cleaning capability of an octagonal tank; （3） a comprehensive account of the hydrodynamics within an octagonal tank can be assessed from simulations. The velocity distribution was uniform with an average velocity of 15 cm/s; the velocity reached 0.8 m/s near the inlet pipe, which can result in energy losses and cause wall abrasion; the velocity in tank corners was more than 15 cm/s, which suggests good water mixing, and there was no particle sedimentation. The percentage of particle removal for octagonal tanks was 90% with the exception of a little accumulation of 〈5 mm particle in the area between the inlet pipe and the wall. This study demonstrated a consistent numerical model of the hydrodynamics within octagonal tanks that can be further used in their design and optimization as well as promote the wide use of computational fluid dynamics in aquaculture engineering.

Effects of spectral composition,photoperiod and light intensity on the gonadal development of Atlantic salmon Salmo salar in recirculating aquaculture systems(RAS)

Artificial lighting regimes have been successfully used to inhibit sexual maturity of Atlantic salmon in confinement.However,when these operations are applied in commercial recirculating aquaculture systems(RAS) using standard lighting technology,sexual maturation is not suppressed.In this study,an L_9(3~3) orthogonal design was used to determine the effects of three factors(spectral composition,photoperiod,and light intensity) on the gonadal development of Atlantic salmon in RAS.We demonstrated that the photoperiod at the tested levels had a much greater effect on the gonadosomatic index and female Fulton condition factor than spectral composition and light intensity.The photoperiod had a significant effect on the secretion of sex steroids and melatonin(P<0.05),and a short photoperiod delayed sex steroid and melatonin level increases.The three test factors had no significant effects on the survival rate,specific growth rate,relative weight gain,and male Fulton condition factor(P>0.05).The optimum lighting levels in female and male Atlantic salmon were LD 8:16,455 nm(or 625 nm),8.60 W/m^2;and LD 8:16,8.60 W/m^2,455 nm respectively.These conditions not only delayed gonadal development,but also had no negative effects on Atlantic salmon growth in RAS.These results demonstrate that a combination of spectral composition,photoperiod and light intensity is effective at delaying the gonadal development of both male and female salmon in RAS.

Evaluation of Feed and Feeding Regime on Growth Performance, Flesh Quality and Fecal Viscosity of Atlantic Salmon(Salmo salar L.) in Recirculating Aquaculture Systems

The effects of different feeds and feeding regimes on growth performance, flesh quality and fecal viscosity of Atlantic salmon （Salmo salar L.） in recirculating aquaculture systems （R.AS） were investigated. Fish （initial body weight of 1677 g＋ 157 g） were fed with four commercial feeds （Nosan salmon-NS, Aller gold-AG, Skretting salmon-SS and Hart ye-HY） in two feeding regimes （80% and 100% satiation） for 78 d. The results showed that salmon specific growth ratio （SGR） and weight gain ratio （WGR） were significantly affected by feed type and feeding regime （P〈0.05）. Feed conversion ratio （FCR） varied between 0.93 and 3.40, which was significantly affected by feed type （P〈0.05）, and slightly improved with increased satiation degree. The activities of digestive enzymes including protease, lipase and amylase were also significantly affected by feed type and feeding regime （P〈0.05）, increasing with satiation degree. Flesh qualities for vitamin E, hydroxyproline （HYP）, liquid loss and muscle pH among all groups showed significant differences （P〈0.05）, ranging from 26.67 to 29.67, while no obvious difference was found in flesh color. Fecal viscosity for different treatments showed no significant difference, though improvement was found in 100% satiation group. From present experiment, it was concluded that both feed type and feeding regime can affect the important quality attributes of Atlantic salmon.

Effect of Hydraulic Loading Rate on the Efficiency of Effluent Treatment in a Recirculating Puffer Aquaculture System Coupled with Constructed Wetlands

Constructed wetlands(CWs) were integrated into an indoor recirculating aquaculture system of obscure puffer(Takifugu obscurus) for effluent treatment. The effect of hydraulic loading rate(HLR) on the efficiency of effluent treatment by CWs was examined for over a month. The CWs were operated under brackish conditions(salinity 7.4–7.6) at 3 different HLRs(0.762, 0.633, and 0.458 m d–1) 3 times, 10 days each. Overall, the CWs exhibited high efficiency in removal of total ammonium nitrogen(by 81.03–92.81%) and nitrite nitrogen(by 99.40%–99.68%). The efficiency of CWs in removal of total ammonium nitrogen, nitrate nitrogen, total Kjeldahl nitrogen, total phosphorous, and total suspended solids(TSS) increased with the decrease of HLR. The CWs operated at the 3 HLRs in a decreasing trend proves to be effective, providing a useful method for effluent treatment in commercial puffer aquaculture systems.

Commercial Production of Tiger Puffer(Takifugu rubripes)in Winter Using a Recirculating Aquaculture System

Tiger puffer(Takifugu rubripes) is a promising species for aquaculture production because of its high value and limited supply. However, in the north of China, using sea cages to culture this species in winter is hampered by the fact that the seawater temperature is extremely low. Here, a large scale commercial production of tiger puffer has been successfully realized using a recirculating aquaculture system(RAS) from 3 October 2012 to 31 May 2013. The RAS was comprised of nine culture tanks(total water volume 200 m3) and stocked with approximately a total of 14400 fish(initial mean weight 160 g). The tiger puffer was hand-fed at a rate of 0.7% of total body weight per day, and the feed conversion rate was(1.21 ± 0.3) kg kg-1. The recycle water in RAS was treated by a sieve bend screen, a foam fractionator, a submerged biofilter, an UV sterilizer and a submersible aerator. During the whole culture period, an excellent water quality control was achieved in RAS. At the end of this experiment, the survival rate of tiger puffer was more than 98%. The final tank densities averaged 31.2 kg m-3, and the final individual mean weight was 440 g.

Solar Thermal Aquaculture System Controller Based on Artificial Neural Network

Temperature is one of the most principle factors affects aquaculture system. The water temperature is very important parameter for shrimp growth. It can cause stress and mortality or superior environment for growth and reproduction. The required temperature for optimal growth is 34oC, if temperature increase up to 38oC it causes death of the shrimp, so it is important to control water temperature. Solar thermal water heating system is designed to supply an aquaculture pond with the required hot water in Mersa Matruh in Egypt as presented in this paper. This paper introduces a complete mathematical modeling and MATLAB SIMULINK model for the solar thermal aquaculture system. Moreover the paper presents the control of pond water temperature using artificial intelligence technique. Neural networks are massively parallel processors that have the ability to learn patterns through a training experience. Because of this feature, they are often well suited for modeling complex and non-linear processes such as those commonly found in the heating system. They have been used to solve complicated practical problems. The simulation results indicate that, the control unit success in keeping water temperature constant at the desired temperature by controlling the hot water flow rate.

Stocking density effects on growth and stress response of juvenile turbot(Scophthalmus maximus) reared in land-based recirculating aquaculture system

Stocking density is widely recognized as a critical factor in aquaculture and a potential source of long-term stress.The influence of stocking density on growth and stress response of juvenile turbot（Scophthalmus maximus, ~3–75g, initial to final weight） was examined in fish held under low（LD, ~0.21–5.31 kg/m^2, initial to final density）,medium（MD, ~0.42–10.81 kg/m^2） and high stocking density（HD, ~0.63–14.27 kg/m^2） for 120 days in a recirculating aquaculture system（RAS）. In this trial, the growth curve for weight of juvenile turbot in RAS, all fitted by the Schnute model. No significant difference was found in growth performance among the three densities until at the final sampling（Day 120）. The final weight and body weight increase（BWI） in the HD group were significantly lower than in other groups（P〈0.05, weight：（75.83±2.49） g,（75.39±2.08） g,（65.72±2.86） g and BWI：（2 436.12±28.10）%,（2 421.29±4.64）%,（2 097.88±20.99）% in LD, MD and HD groups, respectively）. Similarly, the specific growth rate（SGR）, feed conversion ratio（FCR） and coefficient of variation for weight（CV_w） were adversely affected by high stocking density（P〈0.05）. However, there was no difference in survival and Fulton＇s condition factor（K） of turbot among the different groups. Physiological analyses demonstrated a clear increase in the plasma cortisol level and an obvious decrease in growth hormone（GH） concentration in the HD group on Day120（P〈0.05）. There was no significant effect of stocking density on plasma glucose, Cl– and protein levels. All these findings would provide a reference for selecting the optimal stocking density of juvenile turbot in RAS.

Community Structure of Phytoplankton in Pond Industrial Eco-aquaculture System for Megalobrama amblycephala

In order to find out the change pattern of phytoplankton community structure in pond industrial eco-aquaculture system and explain its ecological mechanism,tests were carried out using Megalobrama amblycephala as aquaculture species with two stocking densities.Shannon-Wiener diversity index and Pielou uniformity index were used to study the phytoplankton community structure in aquaculture area( including low stocking density aquaculture area and high stocking density aquaculture area),inlet area,outlet area,purification area,recirculation area,back area of the pond industrial eco-aquaculture system.The results showed that a total of 92 species of 5 phyla were identified,including 46 species of Chlorophyta,15 species of Cyanophyta,15 species of Euglenophyta,10 species of Bacillariophyta,5 species of Cryptophyta,and 1 species of Pyrrophyta.The numbers of phytoplankton species,biodiversity indexes,uniformity indexes,Chlorophyta biomass and its proportion in total phytoplankton followed the order of inlet area,purification area,recirculation area,back area > low stocking area > high stocking area > outlet area.The total biomass of phytoplankton,Cyanophyta biomass and its proportion in total phytoplankton followed the order of inlet area,purification area,recirculation area,back area < low stocking area < high stocking area < outlet area.However,all these parameters showed no significant differences or change rules among inlet area,purification area,recirculation area,back area.It could be concluded according to the biodiversity that the water quality in outlet area was at middle pollution level,the water quality in high stocking area was in light pollution level,and the water quality in other 5 areas were at clean level,which suggested that the water quality was in good states except that in outlet area,and the pond industrial eco-aquaculture system functioned well.

Application of Constructed Wetlands on Wastewater Treatment for Aquaculture Ponds

A group of constructed wetlands （CWs） were applied to the recirculating aquaculture system. This study assessed the performance of CWs in treating the aquaculture wastewater, examined the water quality condition of aquaculture ponds and the growth and the survival rate of ＂target＂ species （Ictalurus punctatus and Megalobrama amblycephala）. The results showed that CWs were effective on reducing the concentrations of 5-day biochemical oxygen demand （BOD5, at 70.5%）, total suspended solids （TSS, at 81.9%）, chlorophyll a （Chl-a, at 91.9%）, ammonium （NH4^＋, at 61.5%） and nitrate nitrogen （NOa-N, at 68.0%）. Effect of CWs on phosphate （PO43 -P） removal was relatively lower （at 20.0%）. The concentrations of BODs, TSS, Chl-a, NH4^＋ and TN, TP in the recirculating culture pond were significantly lower than that in the control pond（ p〈0.05 ）. CWs could help to increase total yield, survival rate of the ＂target＂ species and significantly decrease feed conversion ratio （ p〈0.05 ）.

Establishment of NH_3-N Prediction Model in Aquaculture Water Based on ELMAN Neural Network

In the present study, ELMAN artificial neural network model was developed to predict the change of NH3-N in aquaculture water. The in- dexes including feed ration, dissolved oxygen in water, water temperature, air temperature, water turbidity, rainfall were recorded and chosen as the input variables, while the NHz-N content in the corresponding pond was chosen as output variable. The above data were collected everyday from June to October in 2014 and were used to develop model in this test, and the data collected in November of 2014 were chosen to evaluate the developed model. The results showed that the changing trend of NH3-N in aquaculture water could be simulated well by the model, the predictive absolute error mean was 0.016 mg/L, and Nash-Sutcliffe efficiency coefficient was 0.74. The prediction model based on ELMAN neural network had a strong ability to describe the nonlinear dynamic changes of NH3-N content in aquaculture water, and it showed the good adaptability and accu- racy in practical application.

Foundations of Programmable Process Structures for the unified modeling and simulation of agricultural and aquacultural systems

This research paper defines the theoretical foundations and computational implementation of a non-conventional modeling and simulation methodology,inspired by the needs of problem solving for biological,agricultural,aquacultural and environmental systems.The challenging practical problem is to develop a framework for automatic generation of causally right and balance-based,unified models that can also be applied for the effective coupling amongst the various(sophisticated field-specific,sensor data processing-based,upper level optimization-driven,etc.)models.The scientific problem addressed in this innovation is to develop Programmable Process Structures(PPS)by combining functional basis of systems theory,structural approach of net theory and computational principles of agent based modeling.PPS offers a novel framework for the automatic generation of easily extensible and connectible,unified models for the underlying complex systems.PPS models can be generated from one state and one transition meta-prototypes and from the transition oriented description of process structure.The models consist of unified state and transition elements.The local program containing prototype elements,derived also from the meta-prototypes,are responsible for the case-specific calculations.The integrity and consistency of PPS architecture are based on the meta-prototypes,prepared to distinguish between the conservation-laws-based measures and the signals.The simulation is based on data flows amongst the state and transition elements,as well as on the unification based data transfer between these elements and their calculating prototypes.This architecture and its AI language-based(Prolog)implementation support the integration of various field-and task-specific models,conveniently.The better understanding is helped by a simple example.The capabilities of the recently consolidated general methodology are discussed on the basis of some preliminary applications,focusing on the recently studied agricultural and aquacultural cases.

Dynamic simulation based method for the reduction of complexity in design and control of Recirculating Aquaculture Systems

In this work we introduce the“Extensible Fish-tank Volume Model”that can reduce the complexity in the design and control of the Recirculating Aquaculture Systems.In the developed model we adjust the volume of a single fish-tank to the prescribed values of stocking density,by controlling the necessary volume in each time step.Having developed an advantageous feeding,water exchange and oxygen supply strategy,as well as considering a compromise scheduling for the fingerling input and product fish output,we divide the volume vs.time function into equidistant parts and calculate the average volumes for these parts.Comparing these average values with the volumes of available tanks,we can plan the appropriate grades.The elaborated method is a good example for a case,where computational modeling is used to simulate a‘‘fictitious process model”that cannot be feasibly realized in the practice,but can simplify and accelerate the design and planning of real world processes by reducing the complexity.

Overview of aquaculture systems in Egypt and Nigeria,prospects,potentials,and constraints

Fish farming is considered an important agricultural activity that is capable of ending nutritional deficiencies of the world and contributing to poverty reduction.Its proponents argue that aquaculture will meet the food security needs of millions of people in developing countries who will benefit from relatively inexpensive protein,while depleted capture fisheries are allowed to replenish.Egypt is Africa’s leading aquaculture country,followed by Nigeria with similar production systems.The dominant species of fish cultured in Egypt and Nigeria are Tilapia and African catfish,respectively.The aquaculture industries in these two counties are very promising,as there is a presence of water bodies,some institutional commitment,and high demand for fish among others.Despite some gains made by the countries and the huge potential of the aquaculture sector,it is however bedeviled with constraints such as low technology adoption,inadequate supply of fingerlings,high cost of fish feed,etc.This work is an overview of the aquaculture sectors of Egypt and Nigeria,which includes the production systems,prospects,and potentials of the sector and the constraints that affect aquaculture.

Microcystin Accumulation in Nile Tilapia, <i>Oreochromis niloticus</i>and Giant Freshwater Prawns, <i>Macrobrachium rosenbergii</i>in Green Water System Cultivation

Phytoplankton including blue-green algal or cyanobacterial blooms frequently occurred in aquaculture ponds. Some cyanobacteria produced cyanotoxins that may accumulate in the food web and eventually in the aquaculture products. In this study, accumulatation of microcystins in Nile tilapia (Oreochromis niloticus) and giant freshwater prawn (Macrobrachium rosenbergii) cultured in green water system was investigated.Nile tilapia was cultured in green water system and fish food;green water system with Microcystis aeruginosa Kützingand fish food and green water system with M. aeruginosa. Giant freshwater prawn was cultured: in green water systems with and without toxic M. aeruginosa. Microcystins of 8.32±0.76 and9.35±1.45μg·kg—1 d.w. were detected in fish cultured in green water system with M. aeruginosa and fish food and in green water system with M. aeruginosa, respectively. Microcystins of 14.42±1.63 μg·kg—1 was found in prawn samples. It implied that aquaculture products were likely to be contaminated with microcystins. This finding is useful for aquaculture in terms of food safety.

中国深远海养殖产业发展形势与对策

为了加快推进中国海洋渔业产业转型升级,拓展海水养殖新空间,落实“大食物观”,保障粮食安全,文章阐述了中国深远海养殖产业发展现状,从养殖规模、养殖设施、经营主体、政策导向等方面进行分析。对应中国深远海养殖提高产业竞争力和可持续发展的要求,围绕中国深远海养殖产业如何提质增效,剖析阐明了目前主要存在生产布局不合理、设施装备和养殖技术水平有待提高、产业链配套不够完善、生产安全亟待加强等问题。并在此基础上提出了优化养殖生产布局、推动全产业链发展、规范养殖生产行为、科技引领创新发展等对策建议。旨在为推进中国深远海养殖产业规范有序、健康高效发展提供参考。

海带病害诊断防治专家系统研究

海带病害诊断和防治是保障海带健康养殖的关键。为了提高海带养殖用户的病害诊断和防治水平,对海带病害诊断专家系统进行了研究。研究了知识获取,以学术期刊发表的文献为主,同时辅以专家调研,收集整理31种海带病害;选择产生式规则描述知识,并构造了规则库;采用正向推理进行病害诊断。该系统采用JSP+Sevlet+JavaBean实现,可以满足海带养殖用户对病害诊断防治的需求,并指出了未来研究方向和内容。

罗非鱼混养对广西三江传统稻渔综合种养系统环境及其菌群多样性的影响

研究罗非鱼混养对广西三江传统稻渔综合种养系统环境的影响,可为科学推广稻田金边鲤-罗非鱼混养模式提供基础。2021年5-10月设置3个试验组和1个对照组研究不同密度混养对种养系统环境及菌群多样性的影响,其中试验组内进行罗非鱼和金边鲤的混养,对照组为鲤单养组。结果表明,金边鲤的生长未受到罗非鱼混养的影响;高通量测序结果显示水体中的主要菌群为变形菌门(Proteobacteria)和放线菌门(Actinobacteria),其次为拟杆菌门(Bacteroidetes)、厚壁菌门(Firmicutes)和蓝菌门(Cyanobacteria),主要功能为化能异养和有氧化能异养;底泥中的主要菌群为变形菌门和绿弯菌门(Chloroflexi),其次为酸杆菌门(Acidobacteria)、广古菌门(Euryarchaeota)和蓝菌门,主要功能类群为甲烷生成和化能异养。罗非鱼高密度混养组稻田底泥中的总氮和硝酸盐氮含量有所下降,水体中Polynucleobacter等水质良好的指示物种相对丰度增加,罗非鱼混养对稻渔综合种养系统环境及其菌群产生了有益的影响。

船载投料系统饲料颗粒流落点预测

【目的】为解决网箱养殖中使用船载投料系统的饲料颗粒流落点控制问题,提出一种用于实时分割饲料颗粒流轨迹并精确预测其落点的方法(MLBP)。【方法】考虑到输料管管内参数及饲料颗粒流出口参数获取难度较大,本研究采用高速相机获取饲料颗粒流轨迹图像,并利用提出的混合网络模型分割饲料颗粒流轨迹,以获取轨迹关键信息;为准确预测饲料颗粒流落点,利用BP神经网络的优势,将轨迹信息及投料口高度作为其输入,实现饲料颗粒流落点的预测。【结果】与相关研究方法对比,结合混合网络模型与BP神经网络的MLBP方法的系统单次运行时间降低95%,同时落点预测准确度达到96%,落点的平均误差范围与平均误差百分比也分别降低32.0%和30.5%。【结论】本研究提出的MLBP方法预测精度及实时性均能满足网箱投饵作业需求,可为相关研究提供参考。

大食物系统构建中的水产养殖产业链:韧性挑战及提升对策

作为大食物系统的重要组成部分,水产品为国人提供了超过三分之一的动物蛋白,目前我国水产品总产量已经超过猪牛羊肉总产量之和。由于国内水产品主要来源于水产养殖业,且水产养殖业受国内外市场环境变化及自然条件等各种因素影响较大,因此,水产养殖业产业链韧性将深刻影响着我国水产品供给保障安全。本文基于国家统计局数据和调研数据,分析发现我国水产养殖产业链韧性面临抵抗风险能力弱、受冲击后恢复力不够、产业转型力不强等主要挑战。基于此,从加强科技研发与集成、完善渔业保险制度、打造“一条鱼产业链”、加强质量监管、完善资源管理政策等方面提出加强水产养殖产业链韧性的建议。

稻田-沟渠协同净化池塘养殖尾水效果

为了实现养殖尾水达标排放和循环利用,本研究构建了稻田-农沟-强化沟协同净化系统,考察了各净化单元对池塘养殖尾水中TN、TP、COD_(Mn)和TSS的处理效果,并采用水质标识指数法评价其去除特征和效果,通过浓度沿程衰减的模型拟合分析了相关水质指标沿流程变化规律。结果显示:净化系统出水中TN、TP、COD_(Mn)和TSS浓度平均值分别为1.33、0.19、6.61和12.00 mg/L,去除率分别为86.73%、89.26%、85.77%和93.68%。池塘养殖尾水经净化系统处理后综合水质得到明显改善,其中主要污染物TN得到了显著改善,相关水质达到《淡水池塘养殖水排放要求》(SC/T 9101—2007)一级排放要求;TN、TP和COD_(Mn)沿流程变化规律符合线性削减模型。结果表明稻田-沟渠系统可用于池塘养殖尾水的达标排放。