Performance study of annular settler with gratings in circular aquaculture tank using computational fluid dynamics

The use of recirculating aquaculture systems (RAS) permits the production of fish with a small amount of water and they are an alternative to the scarcity and pollution of water resources. The implementation of an annular settler made by concentric cylinder in an RAS tank allowed the optimal growth conditions of the fish and improves the removal of solids naturally with the presence of low water velocities in the sedimentation zone. The hydrodynamic analysis conducted in this study using computational fluid dynamics allowed the evaluation of different parameters for the geometric design of the settler and its effect on the velocity flow fields that directly affect the particle sedimentation process. Through the evaluation of different geometric configurations of the settler, the use of gratings in the perimeter of the settler with maximum height h_r = 1/6h, width and separation of 0.5h_r, for tank diameter (D) to water depth (h) ratios (D/h) less than 6 was established. These conditions produced velocities between 15−25 cm/s into the cultivation zone, optimal for fish growth. In addition, with the perimetral gratings, velocities less than 2 cm/s are generated inside the settler, situation that benefits the settling of particles and self-cleaning of the tank.     

Modeling hydrodynamics and path/residence time of aquaculture-like particles in a mixed-cell raceway (MCR) using 3D computational fluid dynamics (CFD)

A three-dimensional (3D) simulation of a commercial-size mixed-cell raceway (MCR) was performed using computational fluid dynamics (CFD). Hydrodynamics of the MCR were fully characterized and validated against experimental data. A simulation of path and residence time of aquaculture-like particles was also conducted to understand solids removal mechanisms and potential efficiencies within a mixed-cell. A structured 3D grid model of one mixed-cell was constructed using 250,000 hexahedral elements, and simulations were conducted using the Realizable k–ɛ turbulence model. From the results of the CFD simulations, average cell rotational velocities, radial velocity profiles, and velocity contour and vector plots were generated at three different water depths. As observed in experimental trials conducted by the authors, predicted velocity contours and vector plots revealed the development of a strong rotational flow in each mixed-cell with lower velocity zones at the center and corners of the cells. Also, a linear trend of increasing rotational velocities from the cell's center to its circumferential perimeter was described. Good fluid-flow pattern agreement was observed between the experimental and predicted vector and contour plots. Average rotational velocities at the bottom (95 cm depth), middle (50 cm depth), and top (20 cm depth) planes of the mixed-cell (1-m water depth) were 17.2, 14.9, and 13.7 cm/s, respectively. Comparison of these velocities with the observed values revealed an overall agreement of nearly 96%. Similarly, when the average velocities at radial distances of the MCR were compared at the three depths, the correlation between the experimental and predicted data was on the range of 89–95%.Simulations of aquaculture-like particles trajectories revealed that roughly 100% of particles larger than 500 μm settled and were removed in less than 15 min through the mixed-cell’ central drain. Also, 100% of the 100-μm particles were removed within one mixed-cell hydraulic retention time (HRT) cycle, with approximately half being removed by the bottom-center drain and half being removed via the upper-side drains. Only 50% of the 10-μm particles was removed; and this mainly occurred through the upper-side drains of the mixed-cell after 17 HRT cycles. Smaller particles appeared to stay in the tank for an indefinite period of time.     

Prediction of water velocities in circular aquaculture tanks using an axisymmetric CFD model

Computational fluid dynamics (CFD) software was used to construct two-dimensional axisymmetric simulations of the turbulent flow inside 1.5, 5, 9.15 and 10 m tanks containing rotating water. The water rotation was induced mathematically by either placing a rotating cover on the surface of the water or locating a tangential water inlet near the top of the side wall. Central and side drains evacuated the water from the tank when using an inlet. The rotating cover produced a forced vortex in the tanks similar to the one observed in actual rearing tanks when the majority of the flow is leaving via the side drain. The predicted flow structure in tanks with an inlet can be divided into three regions: a narrow region along the side wall where the rotating water is moving down toward the floor, a thin boundary layer along the floor where the rotating water is moving radially inward, and a large region in the bulk of the tank where radial and axial velocities are small and the tangential velocity is independent of elevation but varies with radial position. Calculations were performed with the k-ε (RNG) and Reynolds stress turbulence models. Converged solutions were easier to obtain with the k-ε (RNG) model but only the Reynolds stress model could predict the strong vortex which is experimentally observed to form in the central portion of the tank as the flow leaving via the center drains is increased. The simulations predict that the thickness of the floor boundary layer is proportional to the tank diameter and that the radial velocity within the floor boundary layer is maximum at an elevation equal to about 10% of the boundary layer thickness. At any given radial position, the maximum value of the radial velocity next to the floor is between 15 and 45% of the tangential velocity in the bulk of the tank. Predicted shear stresses along bounding surfaces were used to obtain correlations for the side-wall and floor friction coefficients in terms of the Reynolds number. These correlations were in turn substituted in an overall moment balance to obtain an analytical model for predicting the maximum tangential velocity V_θw near the side wall of multi-drain rearing tanks. The predictions of the analytical model are in excellent agreement with V_θw values reported in the literature for tanks with diameters ranging from 1.5–15 m and indicate that the drag from inlet structures is non-negligible. The results demonstrate that the axisymmetric CFD model can simulate the main features of the rotating flow inside circular tanks and provide valuable boundary-layer information that is difficult to obtain experimentally.     

Assessment of the quality of pond sediment in aquaculture using simple,rapid techniques

Aquaculture ponds receive inputs of organic matter such as uneaten feed, fertilizer and faeces. Analytical methods for four parameters are described to assess the sediment quality. These parameters are redox potential, pH, the hydrogen sulphide activity potential (pH₂S) and soluble ammonium nitrogen. The techniques are simple, rapid, and are practical on site. Ranges encountered are given and safe ranges suggested.     

养殖沉积环境中气单胞菌属细菌的实时荧光定量PCR检测方法的建立

利用GyrB基因的特异性引物建立沉积环境中气单胞菌属细菌的实时荧光定量PCR检测方法。将已知浓度的气单胞菌菌液加入灭菌的沉积物样品中,作为模拟沉积物样品。通过选择和优化沉积物DNA提取方法、特异性引物、标准曲线模板,建立沉积环境中气单胞菌属细菌准确检验的实时荧光定量PCR方法,同时验证该方法的特异性、灵敏性、重复性。结果表明,采用改进的溶菌酶-SDS温和裂解法提取沉积物DNA,以扩增GyrB基因片段的IAF和IAR为特异性引物,并直接以模拟沉积物样品DNA为标准品构建标准曲线,可以建立适用于定量检测沉积环境中气单胞菌属细菌的实时荧光定量PCR方法。该方法可灵敏、特异、准确地定量检测刺参养殖池塘底泥中气单胞菌属中不同种的细菌,检出效率可达103CFU/g。统计分析显示,变异系数为0.21%-0.80%,均小于5%,表明重复性良好。     

Microbiological indicators for aquaculture impact in Mar Piccolo (Taranto, Italy)

The mussel and fish-farming impact was investigated both in pelagic and sediment environments of Mar Piccolo in Taranto. We studied the yearly distribution of microbiological indicators (heterotrophic bacteria and coliforms), in relation to physical and chemical parameters of surface water at three different sites, characterized by mussel farms, fish cages and Citro springs. The heterotrophic bacteria and Clostridium perfrigens distribution were also examined in relation to organic content and granulometry of sediments. The urban sewages affected the quality of waters of the mussel site, by increasing faecal coliforms in the entire basin during summer. In the benthonic environment the aquaculture activity increased the bio-deposition of the sediment, causing changes in the abundance and the composition (heterotrophic bacteria/clostridia ratio) of microflora. A significant increase of heterotrophic bacteria in the warm season was observed. The clostridia proved to be a good indicator of impact of organic matter because they were significantly higher in the sites than the control stations.     

Applications of computational fluid dynamics to modeling hydrodynamics in tilapia rearing tank of Recirculating Biofloc Technology system

Biofloc Technology (BFT) has been widely used in tilapia rearing. However, the Total Suspended Solids (TSS) at the bottom of rearing tank will increase to high concentration due to biofloc sedimentation and accumulation. Therefore, it will be have negative effects on the feeding enthusiasm, gill and even survival of cultured species, and especially in the initial stages of larvae culture. The Recirculating Biofloc Technology (RBFT) would be one of the potential solution for the above concerns. To achieve an accurate TSS regulation, the biofloc distribution should be as homogenous as possible. The aim of this work is to specify the optimal bubble size and Hydraulic Retention Time (HRT) to the uniformity of biofloc distribution in a RBFT system through Computational Fluid Dynamics (CFD) method. For this, a three-dimensional and three-phase unsteady transient model was developed to simulate the hydrodynamics in a gas-liquid-solid tilapia rearing tank based on the commercial software Workbenching 15.0. Firstly, to achieve a more reliable prediction, the influence of the grid types and the computation turbulence model (Standard, Renormalization-Group (RNG), Realizable) to the simulation result were discussed by contrasting the simulations and experiments results of solid holdup at dimensionless radial position. Secondly, appropriate mesh size (181395 elements) and mixture standard k-e model were implemented to study the effect of bubble size and HRT on solid distribution uniformity. Simulations were performed by using three different mean bubble sizes (diameter = 1, 2, 3 mm) and three different HRTs (0.56, 1.13, and 2.25 h) to study the sensitivity of the results to the uniformity of the biofloc distribution, respectively. The results showed that to get a better biofloc distribution, the bubble size should be range in 1 mm and 2 mm, and as the HRT decreasing, the distribution of biofloc distribution will be more homogeneous (0.45 ≤ HRT ≤ 0.56 h). This paper provides an essential data set for determining the bubble size and HRT in production, as well as evaluating the accuracy of various CFD models for capturing the complex flow field in a BFT rearing tank.     

Seasonal dynamics of microbial community in an aquaculture system for Nile tilapia (Oreochromis niloticus)

Studies on bacterial abundance and diversity will improve the understanding of the microbial ecology to optimize aquaculture production, water quality, disease control and environmental impact of effluents. We comparatively evaluated an aquaculture system in dry and rainy seasons by Fluorescent in situ Hybridization (FISH) and culture‐dependent methodology. Overall, a negative correlation between seasonality in bacterial and flagellates abundance was observed. Alpha‐, beta‐, gamma‐proteobacteria and Cytophaga‐Flavobacter were observed with seasonal variation. Putative pathogenic bacteria such as coagulase‐negative Staphylococcus, non‐fermenter Gram‐negative rods (Pseudomonas sp. and Burkholderia sp.), and Enterobacteriaceae were also detected in this study with significant seasonal variation. Focusing on medically important bacteria, our data show that microbial diversity in the environment associated with aquaculture, as it is practiced, may be altered in growth ponds used for fish cultivation. As an ecological consequence, potentially pathogenic bacteria might be released in high concentrations to the downstream environments posing potential threats to human and animal health.     

石斑鱼循环水养殖系统微生物群落结构

通过16S rRNA基因片段高通量测序研究了褐点石斑鱼(Epinephelus fuscoguttatus)和东星斑(Plectropomus leopardus)循环水养殖系统水体细菌种群结构。结果显示石斑鱼循环水养殖系统中优势细菌类群为变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanobacteria)、梭杆菌门(Fusobacteria)、厚壁菌门(Firmicutes)和硝化螺旋菌门(Nitrospira)。其中养殖塘、固液分离池、沉淀池和蛋白分离池中主要优势细菌为γ-变形菌纲(Gammaproteobacteria),紫外消毒池和补氧池中则以a-变形菌纲(Alphaproteobacteria)为主,而生物滤池中两者比例接近,均为优势种群。从养殖塘到补氧池细菌多样性指数先降低后升高,生物滤池中达到最高值,之后再次下降至紫外消毒池中达到最低值,补氧池中有所回升。PCoA分析和聚类分析结果表明,养殖水在紫外消毒前后其细菌群落组成有着明显的差异。水质理化指标检测表明,经过净化处理后,循环系统的养殖水溶解氧含量上升,氨氮和亚硝酸盐含量下降并维持在较低的浓度。环境因子与细菌群落结构相关性分析结果表明,磷酸盐、pH、溶解氧和温度等指标可能对细菌群落结构影响相对较大,但未发现两者间有很显著的相关性,这可能与实验样本较少有关。     

冻融期刺参养殖池塘沉积物菌群结构特征及其影响因素

本研究以我国北方典型岸基半开放刺参(Apostichopus japonicus)养殖池塘为对象,利用高通量测序技术构建冻融期刺参养殖池塘沉积物菌群16S rRNA基因测序文库,解析封冰期、融冰期和化冰期刺参养殖池塘沉积物菌群结构特征,并查明影响菌群结构的主导环境因子。结果显示,冻融期刺参养殖池塘沉积物菌群丰度和多样性表现为整体下调趋势,在融冰初期呈现显著性波动(P<0.05)。冻融期刺参养殖池塘沉积物菌群结构呈现显著性差异,封冰期、融冰期和化冰期差异菌群分别隶属于厚壁菌门(Firmicutes)、酸杆菌门(Acidobacteria)和软壁菌门(Tenericutes)。尽管不同阶段微生物相对丰度比例不同,但第一优势菌门均隶属于变形菌门(Proteobacteria),相对丰度高于49.04%;次优势菌门则呈现出显著性变化,其中,封冰期为拟杆菌门(Bacteroidetes),融冰期为绿弯菌门(Chloroflexi)和放线菌门(Actinobacteria),化冰期为浮霉菌门(Planctomycetes)。环境因子与菌群相关性分析表明,冻融期刺参养殖池塘沉积物菌群结构与环境因子具有显著相关性(P<0.05),温度、盐度、总氮和总有机碳是沉积物菌群的主导环境因子。本研究将为刺参养殖池塘精细化管理提供理论依据。     

Use of treated mine water for rainbow trout (Oncorhynchus mykiss) culture: a production scale assessment

In previous proof-of-concept work, it was shown that the use of treated coal mine water for rainbow trout (Oncorhynchus mykiss) culture in a cage was technically feasible, though only a 50-fish bioassay was grown and no work on production-related issues was conducted. To further advance the use of treated mine water, an under-utilized water resource throughout Mid Appalachia, work was conducted to assess the effects of using treated coal mine water for the intensive production of rainbow trout in a flow-through system. During this study, comprehensive water quality data were collected to supplement fish weight and length data taken during routine monthly sampling events. The 8000 fish grew well in the raceway system over the 9 months of production, where a feed conversion ratio of 1.4 and a condition factor of 5.1 × 10⁻⁴ were measured with stocking and harvest densities of 26.4 and 50.2 kg/m³, respectively. Further, total net production was 3275 kg (7220 lb) with 98.6% survival. Throughout the study, dissolved ion concentrations (Fe, Al, Mg, Ca, and SO₄) often exceeded recommended tolerance limits. Further, elevated ammonia nitrogen concentrations generated from a component of the mine water-treatment process were identified as a potential limiting factor for aquaculture development. However, when the non-ideal effects of high ionic strength and the speciation of dissolved metal–ligand complexes were taken into account, the concentrations of free metal ions were within recommended tolerance limits.     

Optimization of blue mussel (Mytilus edulis) seed culture using recirculation aquaculture systems

By introducing recirculation aquaculture systems (RAS) in the nursery phase of the blue mussel (Mytilus edulis) (17–18 mm), we aimed at a similar growth and survival and a similar water quality compared to the commonly used flow‐through systems (FTS). To calculate water flow and size of the biofilter, a series of experiments were done to determine clearance rate (9.26 mL min^?1), pseudo faeces threshold (60 000 cells Pavlova lutheri mL^?1), nitrogen production (0.00065 mg TAN h^?1 ind^?1 and 1.6 × 10^?5 mg NO₂–N h^?1 ind^?1) and oxygen consumption (0.03 ± 0.01 mg O₂ h^?1 ind^?1). RAS showed no significant differences in water quality (0.06 mg TAN L^?1; 7.7 mg O₂ L^?1) and growth performance of mussel seed specific growth rate (SGR = 5% day^?1) after the experimental period of 4 weeks compared with FTS. The low water refreshment, 10% per day, as well as the constant chlorophyll concentrations (9.76 ± 1.06 μg L^?1), suggests the potential of RAS as culture system for mussel seed.     

Sedimentation from mussel (Perna canaliculus) culture in the Firth of Thames, New Zealand: Impacts on sediment oxygen and nutrient fluxes

Shellfish aquaculture is growing worldwide and previous studies have shown a range of associated environmental impacts. In the Firth of Thames, New Zealand, there are more than 2000 ha of existing and approved farm area with applications pending for approximately another 6000 ha, however, no previous studies have examined the impacts of mussel culture in this region. To determine the impact of a mussel farm (45 ha) in the Firth of Thames we measured sedimentation rates by deploying sediment traps, sediment characteristics by collecting sediment cores and sediment oxygen and nutrient fluxes by deploying benthic chambers in four seasons. Sedimentation under the farm was increased by 106 g m^− 2 d^− 1 compared to the reference site. Similarly sediments under the farm had elevated organic carbon, nitrogen, chlorophyll a and phaeopigment concentrations indicative of the additional organic input due to bivalve biodeposition. Oxygen consumption was higher under the farm compared to a reference site (1.1-2.1×) but this increase was only significant (p < 0.001) in summer when rates reached 3083 μmol m^− 2 h^− 1 under the farm. Ammonia release rates ranged from 80 to 319 μmol m^− 2 h^− 1 and were higher under the farm compared to the reference site in spring (1.8×, non-significant p = 0.588) and autumn (3×, significant p = 0.006) but in summer release rates at the reference site (275 μmol m^− 2 h^− 1) were 1.4× higher than those under the farm. Nitrate fluxes (3.1 to 21.8 μmol m^− 2 h^− 1) were significantly (p = 0.001) higher at the farm site. Oxygen and nutrient fluxes generally demonstrated the typical response to increased organic input due to sedimentation from mussel culture. Unusually low nitrogen release rates in summer may indicate enhanced denitrification under the farm. Benthic regeneration at the reference site could supply 74% of nitrogen required by pelagic primary producers whereas under the farm it could account for 94%. This demonstrates the importance of benthic nutrient regeneration in this region and that mussel culture can lead to a redistribution of nutrients. The farm we studied is small and located in a high-energy environment and impacts from larger farms or in areas where biodeposit dispersal is limited are likely to be even more significant and we suggest that site-specific hydrodynamic and biogeochemical conditions have to be taken into account when planning new mussel farms to prevent excessive modifications of nutrient dynamics.     

Assessment of impact of aquaculture on Kolleru Lake (India) using remote sensing and Geographical Information System

Aquaculture is one of the fastest growing food industries and the rapid growth of aquaculture worldwide has resulted in growing concerns about its impact on important ecosystems. Kolleru Lake, India's largest fresh water body, and Ramsar site have undergone tremendous changes due to the development of aquaculture. To assess the impact of aquaculture on Kolleru, satellite data were found appropriate because of the synoptic‐detailed overview and accuracy. Satellite data of IRS 1D, LISS III from 2004 and Survey of India topographic maps from 1967 were processed using image processing techniques in erdas imagine and analysed in Geographical Information System (GIS) such as arc gis 9.1. Land use map prepared from the satellite data was verified in the field using Global Positioning System to check the land and water use classes and its areal extent. It was estimated from the topographic maps of 1967 that the total lake boundary area was 180.38 km², in which 70.70 km² had water throughout the year and 100.97 km² had water during the rainy season. The digital image processing of 2004 satellite data revealed that Kolleru was no longer a lake and the lake area of 62.65 km² (34.73%) only remained in a degraded state, extensively colonized by macrophytes. The total loss of lake area was 109.02 km² between 1967 and 2004, in which aquaculture was developed in 99.74 km², which represented 55.3% of the 1967 lake area. The maximum conversion to aquaculture occurred from the lake liable to be inundated during the 1967 rainy season. The area under agriculture was 16.62 km² in 2004, the increase in lake area for agriculture between 1967 and 2004 being 8.22 km² (4.55% of lake). If human induced degradation is allowed to continue, the lake will very soon disappear. Now, the Government of Andhra Pradesh, India, has initiated schemes and laws to restore the lake to its pre‐development state. Lessons learnt from the Kolleru Lake cautioned that there is a need for regular monitoring of important water resources throughout the world to protect the biodiversity of the earth.     

Assessment of the tidal currents and pollutants dynamics associated with shrimp aquaculture effluents in SAMARE coastal lagoon (NW Mexico)

The pollutant dispersion induced by the tidal hydrodynamics was investigated through a modified model in Santa Marìa‐La Reforma coastal lagoon, a body water that receives effluents containing chemicals that are used in shrimp aquaculture. Maxima tidal currents (0.7 ms^?1) were predicted within the main channel. Residual currents, of the order of 0.01 ms^?1, were also predicted. The hypothetical pollutant, released at four selected sites that receive effluents from shrimp aquaculture and agriculture within the lagoon, spread towards the northern and southern inlets. The advection and diffusion processes allow the pollutant in most of the cases, to reach the inlets in about 120 h. The spreading of the pollutant in the coastal lagoon seems to be modulated by the tidal velocity fields. The presence of an area where tidal currents converge in the eastern part of Talchichitle Island suggests that a potential accumulation of pollutants occurs in this site.     

Impact of aquaculture on mangrove areas in the northern Pernambuco Coast (Brazil) using remote sensing and geographic information system

The conversion of mangrove areas into shrimp farming ponds has been indicated as the main activity responsible for the reduction in the area of this ecosystem along the northeastern coast of Brazil. The present study was conducted using remote sensing methods and a geographical information system with the aim of quantifying the participation of this activity in the reduction of the mangrove areas along the northern coast of the State of Pernambuco (northeast, Brazil), where shrimp farming has been implanted in last recent years. From 1973 to 2005, there was reduction of about 2.052 ha of mangrove, 197 ha of which were converted into shrimp ponds. Thus, the real contribution of shrimp farming to this reduction was just 9.6% of the total area. Other anthropogenic activities, such as agriculture, urban expansion and tourism, contributed greatly to the reduction in the mangrove areas along the northern coast of the State of Pernambuco.     

The possibility of application of agglomerate elastomers (EPP) as media for biological bed in aquaculture

The aim of the study was to determine the possibility of experimental media (agglomerate elastomers EPP) application as biological media bed, which serves the purpose of water purification in recirculating aquaculture systems (RAS). RAS enables mass‐production of fish in small volume of water in a limited area. This involves the possibility of multiple usage of water during culture. However, for that purpose of maintaining proper physico‐chemical parameters, water purification from products of metabolism, especially toxic nitrogen compounds, is required. One of the simplest and most effective ways to achieve it is combining application of two types of water filtration: mechanical and biological. It is needed to study new media for biological bed with proper filling is able to purify water from toxic nitrogen compounds.     

Captive breeding of climbing perch Anabas testudineus (Bloch, 1792) with Wova-FH for conservation and aquaculture

Induced breeding of climbing perch, Anabas testudineus was conducted by synthetic hormone Wova‐FH in the intensity level of 0.1, 0.2 and 0.3 mL kg^?1 of body weight respectively. The brooders were injected one time and left to spawn in the spawning hapa in the sex ratio between male and female as 2:1. It was found that at all the intensity level hormone Wova‐FH could enhance the fishes to breed and lay eggs whereas no breeding was observed in control set. The spawning time, quantity of the brooder spawn, fertilization rate, hatching rate and survival rate were quantified in each set of experiment. The egg output/female was significantly higher in 0.3 mL in comparison with 0.1 and 0.2 mL kg^?1 of body weight. The statistical analysis showed significant (P≤0.05) effect between hormone dose on fertilization rate, egg output and hatching rate. The present experiment suggests that Wova‐FH at the dose of 0.3 mL kg^?1 body weight of fish is more effective which might be considered for raising captive population.     

Influence of larval transport and temperature on recruitment dynamics of North Sea cod (Gadus morhua) across spatial scales of observation

The survival of fish eggs and larvae, and therefore recruitment success, can be critically affected by transport in ocean currents. Combining a model of early‐life stage dispersal with statistical stock–recruitment models, we investigated the role of larval transport for recruitment variability across spatial scales for the population complex of North Sea cod (Gadus morhua). By using a coupled physical–biological model, we estimated the egg and larval transport over a 44‐year period. The oceanographic component of the model, capable of capturing the interannual variability of temperature and ocean current patterns, was coupled to the biological component, an individual‐based model (IBM) that simulated the cod eggs and larvae development and mortality. This study proposes a novel method to account for larval transport and success in stock–recruitment models: weighting the spawning stock biomass by retention rate and, in the case of multiple populations, their connectivity. Our method provides an estimate of the stock biomass contributing to recruitment and the effect of larval transport on recruitment variability. Our results indicate an effect, albeit small, in some populations at the local level. Including transport anomaly as an environmental covariate in traditional stock–recruitment models in turn captures recruitment variability at larger scales. Our study aims to quantify the role of larval transport for recruitment across spatial scales, and disentangle the roles of temperature and larval transport on effective connectivity between populations, thus informing about the potential impacts of climate change on the cod population structure in the North Sea.     

One cryptic species of grey mullet (Mugil cephalus mitotype: NWP3) from Taiwan’s waters is worth cultivating for large roes using aquaculture

The grey mullet, Mugil cephalus, is an important aquaculture species in Taiwan. They were thought to be a single fish species in terms of the morphology‐based taxonomy; however, three cryptic species of grey mullet (mitotype: NWP1, NWP2 and NWP3) have been identified within the Taiwan waters. In general, the NWP2 females are known to have small body sizes with large developed ovaries regardless of the cultivation time, whereas the NWP1 females have large body sizes with small ovaries. In this study, the NWP3 females are found to have significantly larger body and ovary weights than do the NWP2 females under the same aquaculture conditions. Therefore, even though the NWP2 females are good fish for producing large ovaries, this study indicates that the NWP3 females have even more potential to produce huge ovaries than do the NWP2 females.