干露及恢复过程中菲律宾蛤仔免疫指标的变化

在滩涂养殖和运输过程中,菲律宾蛤仔经常处于干露状态。笔者研究了蛤仔在干露胁迫和随后的恢复过程中酶活力和免疫相关物质含量的变化,初步揭示了滩涂贝类耐干露的生理学机制。在蛤仔干露12、24、48 h,以及恢复培养2、6、12、24 h时分别取蛤仔鳃和内脏团,测定酶活力及免疫相关物质含量,设持续海水养殖的蛤仔为对照组。结果表明,蛤仔在干露胁迫12 h和24 h时,内脏团AKP活力显著高于对照组(P<0.05);CAT活性在整个实验中与对照组差异不显著(P>0.05),鳃中AKP和CAT活力与对照组差异不大;内脏团SOD活力在干露12 h时显著升高,而鳃中SOD活力在恢复期显著升高(P<0.05);内脏团中MDA含量在干露24 h时显著高于对照组,鳃中MDA含量在干露12 h和24 h时显著低于对照组;内脏团NO含量在恢复海水后6 h时显著高于对照组(P<0.05),而鳃在干露48 h时NO含量显著高于对照组。分析认为,干露过程中,蛤仔呼吸代谢减慢,鳃的生理机能维持平稳或受到抑制,代谢和免疫保护作用主要由内脏团来完成。恢复培养时,随着呼吸作用和血液循环的恢复,鳃逐渐承担起部分抗氧化功能,使机体迅速恢复到正常生理状态。     

Improving feeding strategies for shrimp farming using fuzzy logic,based on water quality parameters

In intensive shrimp farming systems, formulated feed represents the main nutrition source and its adequate management significantly influences the economic feasibility of the farm. Based on that, the present study evaluated two dynamic feeding strategies: fuzzy logic (FL) and mathematical functions (MF). For both strategies, the temperature and dissolved oxygen were modified in a controlled way. A conventional feeding table was the control treatment. The results showed that DO was the parameter that mostly influences the feeding rate (74%) while the temperature also did it, but in a lower grade (26%). The results showed that feed conversion rate (FCR) was significantly better when the FL strategy was used, saving around 35% of feed when compared to the control. An expert system based on FL may replace the traditional feeding strategies with no significant adverse effects on growth, survival and FCR, and may easily be adapted to some other culture systems.     

Development of human-powered fish feeding machine for freshwater aquaculture farms of developing countries

Feeding the fishes rightly has been a problem for the fish farmers and developing suitable feeding devices is one of the most challenging problems faced by aquaculture engineers. Fish farmers of developing nations find manual feeding economical rather than opting for expensive mechanized feeding. In this study, a simple human-powered fish feeding machine which can economically solve the feeding issue in freshwater aquaculture, has been developed. The major parts of the feeder are cylindrical feed drums mounted on a pedal powered shaft, a catamaran barge, propeller and steering arrangements. When the operator pedals, the feed shaft rotates and the feed in the feed drums is metered through the metering holes provided in the feed drums. Human muscle power is used to power feeding operation as well as to propel the feeder. Since the device has been designed to utilize optimum human power for its entire operation, it is energy-efficient, environmental friendly and most importantly affordable. The developed device has been tested in laboratory and has been observed to be successfully operating in field condition while achieving the desired feed rate.     

Numerical model of an aquaculture structure under oscillatory flow

Marine aquaculture is widely distributed in coastal areas. The aquaculture farms generate drag resistance to fluid motion and alter ambient hydrodynamics. Meanwhile, aquacultural structures are subjected to complex flow conditions including waves and currents. With the expansion to more open areas with severe flow field conditions, marine aquacultural structures face greater challenges and risks of damage. Culture unit is an important component of aquacultural structures and shows flexibility in both field observations and laboratory measurements. Underestimating or overestimating the drag resistance of culture units under the action of fluid flow can lead to damage risks or overdesign of the structure. A dynamic model is developed to estimate the deflection of flexible culture units and is incorporated into an aquacultural structure numerical model in this paper. Critical factors for safety as well as routine operation of aquacultural structures are considered including structural responses and mooring line forces. A suspended mussel long line system is taken as an example, and the results show that the calculated value (9.2 kN) of the maximum tension of the north mooring line is in good agreement with the measured data (9.8 kN) under the action of tide flow. The influence of different flow field parameters on structural dynamic responses is investigated. The numerical results indicate that decreasing wave height can reduce maximum mooring line tension and longitudinal and vertical motion amplitude of the main line. The maximum tension of the mooring line generally decreases with the increase of the angle between the main line and the inflow direction under the action of waves and tide flows. In structural design, the arrangement angle of structures can be determined according to the force calculation of mooring lines based on the numerical model. The spacing of culture units and the distance between adjacent long lines can be determined by referring to the motion calculation of structures to avoid damage due to intertwinement of structural components.     

Testing the efficacy of bouncing-bucket nursery systems for enhancing shell strength and thickness in on-bottom cultured Eastern oysters (Crassostrea virginica)

Through physical manipulation, oyster growers can modify the morphological features of young oysters in order to improve their robustness and resiliency to predation. In this study, the efficacy of a novel passive culturing technique using floating buckets that “bounce” oysters prior to the benthic grow-out phase for enhancing shell thickness and strength, while not compromising oyster shape, was investigated. Using a field experiment, we quantified and compared the shell thickness (mm), compressive strength (Newtons), and shape (fan ratios and cup ratios) of juvenile oysters subjected to this bouncing technique with oysters grown in floating bags, the current industry standard. Results indicated that bouncing increased shell thickness and strength for oysters >45 mm shell height compared to control oysters, but also decreased shell thickness and strength for oysters <45 mm shell height compared to control oysters. There was no difference in shell shape between bounced and control oysters, with both groups having similar fan and cup ratios. Ultimately, our results suggest that the size at which bounced oysters are released to the benthos for grow out will dictate the usefulness of bouncing technique for reducing predation-related mortality.     

LED光源在海水养殖水体中传播特征解析

光是影响水生动物生长和发育的重要环境因子，其在养殖水体中的传播特征仍未明确。本研究选取红光(波峰为645 nm)、绿光(510 nm)、蓝光(445 nm)、UVA(355 nm)以及全光谱(蓝光激发硅酸盐荧光粉辐射的白光波长范围可达400~800 nm)5种LED光源，调整辐射照度为60 W/m2，研究其在不同养殖水质环境中的传播规律，为满足室内工厂化水产养殖对象的光生物学需求，实现养殖光环境标准化调控提供参考。结果显示，5种不同光谱特征的LED光源在深井海水中的透光率随水深增加呈降低趋势，不同光源间变化趋势存在差异。当透光水深为10 cm时，绿光透光率最大，为(46.01±4.03)%，UVA最小，为(26.01±2.53)%；当透光水深为150 cm时，各光色透光率均小于1.5%；5种不同光色的光源在水体中的透光率衰减曲线均符合乘幂函数。水体对LED光的吸收在不同的光谱区域是不同的，具有明显的选择性，水对光谱中红外部分的吸收最为强烈，对可见光谱波段中的红色、黄色和绿色光谱区段的吸收也十分显著；LED光源在养殖水体中衰减严重，水深是影响LED光源在水体中传播的主要因素(P<0.01)，其次是总悬浮物(TSS)和化学需氧量(COD)，但不同光源在养殖水体中受TSS和COD含量的影响程度不同。光在水体中的衰减由水对光的吸收以及散射作用引起，且光在不同波段的衰减率主要由水生介质的吸收光谱决定。     

Application of nitrification and denitrification processes in a direct water reuse system for pacific white shrimp farmed in biofloc system

The aim of the present study was to propose a low-cost nitrogen removal system through the nitrification / denitrification process in order to maintain the water quality required for the Pacific white shrimp superintensive cultivation in closed systems without water renewal. The increase in productivity consequently causes the accumulation of organic matter and nitrogenous compounds, especially ammonia nitrogen and nitrite, which in high concentrations can be lethal to aquatic organisms. In addition, the accumulation of solids in the system provides conditions for the emergence of opportunistic pathogens, microalgae booms, and increases the producer's cost of inputs to maintain the equilibrium physicochemical relationships required for shrimp farming. The experimental productive cycle lasted 36 days using Litopenaeus vannamei shrimps with 7.1 g ± 0.56 g and density of 350 shrimps m⁻³. The nitrogen removal efficiency observed during the study period was 71.3 ± 5.3 %, and the shrimp had a survival of 92.9 % and a final weight of 13.1 ± 1.4 g. Thus, we established a system (ammonia and nitrite), capable of managing solids without interaction with the sea, ensuring high biosecurity against exogenous diseases in marine shrimps farms.     

Water quality upstream and downstream of a commercial oyster aquaculture facility in Chesapeake Bay,USA

Oyster aquaculture is an expanding industry in the Chesapeake Bay. Oysters remove nitrogen (N) and phosphorus (P) from the water column through filtration and conversion of phytoplankton into shell and tissue, but also continuously excrete these same nutrients back into the water column as inorganic compounds readily available for plant or algal uptake. The objective of this study was to assess multiple water quality parameters upstream and downstream of a commercial oyster aquaculture facility in the mesohaline region of the Chesapeake Bay. Results of the study indicated a 78.4% average increase in total ammonia nitrogen (TAN) concentration and a 19.4% decrease in chlorophyll-a (Chl-a) concentration downstream of the facility. There was no significant change in the concentration of reactive phosphate (RP), nitrate–nitrogen (NO₃⁻–N), or nitrite–nitrogen (NO₂⁻–N) as water passed through the facility. It was determined that velocity of water through the facility had no influence on the change in TAN or Chl-a concentration from upstream to downstream of the facility. Increased reduction in Chl-a concentration from upstream to downstream was related to higher upstream concentrations of Chl-a. There was no correlation between increased rates of Chl-a removal and downstream TAN. Results of this study suggest that oyster aquaculture can significantly increase the amount of available inorganic nitrogen in the water column immediately downstream of a facility, independent of upstream availability of phytoplankton and flow velocity of water through the facility.     

Assessment of Fatty Acid Composition and Technological Properties of Northern Pike (Esox lucius) Fillets: The Effects of Fish Origin and Sex

The aim of the study was to investigate the effects of northern pike origin (wild vs. farmed) and sex (female vs. male) on chemical composition, including fatty acids, and technological properties of fresh fillets. Fish origin influenced moisture, protein, fat, and ash contents, pH and color of the fillets, and the proportion of 22 out of 25 determined fatty acids, whereas sex affected expressible water, pH, lightness and redness of fillets, and only a single fatty acid (C20:0) proportion. Farmed pike had higher protein and fat content and lower moisture and ash than wild pike. Higher proportion and content of total polyunsaturated and n-3 fatty acids, as well as lower n-6/n-3 ratio, were found in farmed pike. Thus, it can be concluded that the commercial feed positively affected fatty acid proportion and content in the fish tissue and increased its nutritional value.     

Efficiency of producing bioflocs with aquaculture waste by using poly-β-hydroxybutyric acid as a carbon source in suspended growth bioreactors

With additional organic carbon, fish waste can be used as a substrate to produce bioflocs, a protein source for aquaculture animals. In choosing a carbon source, one should consider convenience, cost and biodegradability. This study investigates the efficiency of poly-β-hydroxybutyric acid (PHB), a biologically degradable polymer, as a carbon source to produce bioflocs in suspended growth bioreactors (SGRs), PHB-SGRs, compared with glucose (GLU-SGRs). The C:N ratio in PHB-SGRs could be maintained around 15:1. The volatile suspended solids (VSS) yield was 2.94 ± 0.72 gVSS/g fish waste for PHB-SGRS and 4.90 ± 0.23 gVSS/g fish waste for GLU-SGRs. The recycling rate of nitrogen in aquaculture solid waste was 56 ± 2% and 87 ± 7% for the PHB-SGRs and Glu-SGRs. No significant differences were found in the bioflocs produced and in the crude protein content of the produced bioflocs between PHB-SGRs and GLU-SGRs. PHB-SGRs and GLU-SGRs could remove dissolved inorganic nitrogen from aquaculture wastewater, with average values of 11.82 ± 8.95 and 16.27 ± 3.95 mg/g TSS/d. Because the calculation of the added amount of carbon and the multiple additions of carbon was avoided, PHB is considered to be a good choice as an organic carbon source for this process, even though not all parameters used for assessment were better than those of GLU-SGRs.