不同工作姿态下立式双曲面网板水动力及周围流场特性研究

网板是单拖网中实现网具扩张的重要属具,其稳定状态直接决定拖网网口扩张程度,进而影响渔获效率和经济效益。该研究以立式双曲面网板为研究对象,利用水槽模型试验和数值模拟(Computational fluid dynamics,CFD)探究立式双曲面网板在不同倾斜状态(内、外倾斜,前、后倾斜)和冲角下的水动力性能变化,并对网板周围流场和表面压力进行可视化。结果显示:1)模型试验和数值模拟的网板升力系数均在倾角为0°,冲角为25°时达到最大值,分别为1.69和1.88;而两者的阻力系数均随倾角增大逐渐减小。2)模型试验和数值模拟的升阻比均随倾角增大逐渐减小;当内倾角为5°时,两者的升阻比均达到最大,分别为3.27和3.69。3)压力中心系数Cpb随倾角变化基本保持不变;但当网板处于前倾状态时,Cpc随倾角增大而增加;而网板处于后倾状态时,Cpc随倾角增大逐渐减小。4)CFD结果显示,网板中心面后部旋涡随倾角增大逐渐减小;当网板处于内、外倾状态时,前端流速衰减区随倾角增大逐渐增加;但当网板处于前、后倾状态时,衰减区随倾角增大逐渐减小;网板处于前倾状态时,压力中心随倾角增大逐渐向网板上端翼弦移动,网板处于后倾状态时则出现相反结果。研究结果可为今后研究网板稳定性和合理使用及调整网板提供科学参考。     

南极磷虾拖网网板水动力性能分析

为提高南极磷虾单船拖网低拖速作业时的网具扩张性能,针对一种立式曲面中空式拖网网板,利用水槽模型试验测得不同迎流冲角状态下的升力系数(CL)、阻力系数(CD)和升阻比(K)。结果表明,CL和K值随冲角的增大呈先升后降趋势,CD随冲角的增大呈上升趋势;升力系数最大值CLmax=1.436(冲角α=30°),此时CD=0.649,K=2.213,升阻比最大值Kmax=4.671(α=10°),此时CL=0.981,CD=0.210;工作冲角范围为10°~30°时,南极磷虾拖网网板升力系数CL0.98且升阻比K2.21。比较不同类型网板的水动力性能,南极磷虾拖网网板具有阻力系数较低、升阻比较高的优点,可为进一步优化南极磷虾拖网网板性能提供参考依据。     

基于CFD评估尺度效应对V型网板水动力的影响

按相似准则等比例缩小网板构建物理模型测定其水动力,是研究网板水动力特征的主要方式。基于V型网板,利用计算流体力学(Computational fluid dynamics, CFD)对比分析了3种尺度比(1∶2、1∶3和1∶4)的网板和3种厚度(2、5和10 mm)下的升、阻力系数及流场分布,并将其与模型试验结果进行对比,探究不同物理模型尺度对估算网板水动力的影响。结果表明：1)随着冲角的增加,各尺度的网板阻力系数逐渐增大,升力系数先增大后减小,升阻比逐渐减小;2)在30°冲角之后,网板后部出现明显的分离涡,造成模拟升力减小;3)随着网板模型尺度的增大,网板表面边界层分离效果和尾流区流场分离涡逐渐增强,网板升、阻力及升阻比亦呈增大趋势。网板厚度对流场及升、阻力影响较小,最大升力系数相对于模型试验平均误差为4.97%;4)随着模型尺度增大,网板水动力的预测误差逐渐减小。     

双开缝矩形曲面网板水动力性能及影响参数研究

为满足渔业现代化的发展需求,渔具的改良是其不可或缺的一部分,而网板是提供拖网网衣水平张力主要属具。采用矩形曲面网板有利于提高网板的升力系数和升阻比,而网板开缝有利于减小网板的背面涡流,增加网板的水动力性能,提高网板操作稳定性。为研究小型拖网渔船网板的水动力性能,通过数值模拟的方法,在其他参数一定的情况下,采用控制变量法控制双开缝矩形曲面网板的速度、开缝尺寸以及展弦比等参数的单一变化,研究其对拖网网板水动力性能的影响规律。数值计算结果表明:该网板升力系数和升阻比随冲角的增大呈先增后减的趋势,最佳升阻比出现在冲角为10°左右的时候;速度对网板水动力性能无显著影响;升力系数随开缝尺寸的增加总体呈上升趋势,当开缝尺寸大于50 mm时,升力系数无显著变化,升阻比随开缝尺寸增大总体呈先增后减的趋势;不同展弦比的网板在升力系数达到最大时对应的最佳冲角随展弦比的增加而逐渐减小;同时,升力系数峰值随展弦比的增加呈先增后减的趋势,当展弦比为0.6左右时,升力系数的峰值达到最大。研究结果可为同类型的小型拖网渔船拖网网板的结构优化设计提供更加可靠的参考。     

叶板尺度比例变化对单缝曲面网板水动力性能的影响

利用风洞模型试验研究单缝曲面网板模型,通过改变叶板尺度比例对单缝曲面网板其水动力性能变化进行了考察。试验中采用了3种不同叶板尺度比例的模型网板,在风速28 m/s,冲角(α)范围0°~70°时,利用塔式六分量机械-应变天平对网板所受到的阻力、升力和力矩进行了测量,通过换算得到网板的阻力系数Cx、升力系数Cy、俯仰力矩系数Cm、压力中心系数Cp和升阻比Cy/Cx,对比各系数的变化分析各模型网板的水动力性能差异。结果显示,2号与3号模型网板的最大升力系数更高,分别为1.919(α=30°)和1.911(α=30°),导流板尺度比例较小的1号与2号模型网板的最大升阻比较高,分别为5.991(α=10°)和5.994(α=12.5°),且2号模型网板的作业冲角选择范围较大;在稳性对比方面,导流板尺度比例较小的1号模型网板的Cp变异系数最低,为6.02%,说明1号模型网板的稳性更好。研究结果可为拖网网板的结构优化设计提供参考。     

立式V型曲面网板的水动力性能

采用正交优选法来考察网板板面折角、展弦比以及后退角对立式V型曲面网板水动力性能的影响。试验结果证明影响网板水动力性能的最重要的因素是网板板面折角,其次是展弦比和后退角。当网板的板面曲率为14%、板面折角为12°、展弦比为1.60、后退角为10°时,网板具有较高的水动力性能。当冲角为25°和28°时,网板的升力系数均为1.68。另外,通过对优选网板添加模拟海底的试验证明,网板在底层作业时,其临界冲角从28°减小为25°;在常用工作冲角范围内,网板在底层时的扩张性能要高于中层,同时,网板的升阻比也略有上升,并能在较宽的冲角范围内持续保持较高的扩张性能。     

加筋结构对V型网板水动力性能的影响研究

网板作为拖网渔具的重要属具,其水动力性能对拖网渔具的可操作性和渔获效率均有十分重要的影响。以我国近海拖网渔船配置的加筋V型网板为研究对象,通过与传统无筋V型网板的水动力性能对比分析,研究加强筋对V型网板水动力性能的影响机理,并通过开展动水槽实验对数值计算结果的有效性进行验证。在此基础上,通过改变展弦比、板面折角、加强筋尺寸等设计参数,研究其对加筋V型网板水动力性能的影响规律。结果表明,在大冲角(40°以上)时,加筋V型网板的升、阻力系数与传统V型网板相比呈显著下降趋势;加强筋的存在较为明显地降低了V型网板在最佳工作冲角(10°左右)下的升阻比;增设加强筋后,V型网板的最大升阻比依然会随展弦比的增加而呈逐渐增大的趋势,但不同的展弦比下V型网板的最大升阻比有较为明显的降低;加筋V型网板的板面折角变化引起最佳冲角的改变,但最大升阻比会随板面折角的增加呈现显著增大的趋势;加强筋间距较大时会引起V型网板最大升阻比的明显降低,其尺寸的增加也会在一定程度上降低网板的升阻比。     

展弦比和最大相对弯度对南极磷虾拖网网板水动力学性能的影响

为了研究展弦比和最大相对弯度对南极磷虾拖网网板水动力学性能的影响,通过水槽模型实验分析网板临界冲角(α0)、最大升力系数(CL_(max))、临界冲角时的升阻比(Kα0)和最大升阻比(K_(max))等主要水动力学性能参数的变化规律。结果表明:1)展弦比对CL_(max)、K_(max)和Kα0值的影响极显著(P0.01),对α0无显著影响(P0.05)。随着展弦比的增加,CL_(max)和K_(max)呈上升趋势,Kα0呈先升后降趋势,λ=2.0时Kα0值相对较高。随着展弦比的增加,α0分别呈下降(最大相对弯度为12%和14%)和上升(最大相对弯度为8%)趋势。最大相对弯度为10%时,α0在27.5°~30°间波动变化,趋势线基本保持水平。2)最大相对弯度对CL_(max)和K_(max)值的影响极显著(P0.01),对α0值的影响显著(0.01P0.05),对Kα0无显著影响(P0.05)。展弦比和最大相对弯度两者间交互项对Kα0影响极显著(P0.01),而对CL_(max)和K_(max)无显著影响(P0.05)。随着最大相对弯度的增加,CL_(max)和α0呈上升趋势,K_(max)呈下降趋势。综合考虑拖网网板的水动力学性能,实际应用中建议立式双弧面网板最大相对弯度设计为12%,展弦比设计为2.0,此时网板的主要水动力学性能参数均为前40%水平,具有最大升力系数和最大升阻比相对较高、阻力系数较低的优点。     

倾斜状态对V形网板水动力和周围流场特征的影响

为了探究 V 形网板在各种工作姿态下水动力特性的变化规律, 作者采用数值模拟(computational fluid dynamics, CFD)方法对比了 4 个展弦比(0.4、0.5、0.6、0.7)和 4 个板面夹角(16°、19°、22°、25°)的网板的水动力性能, 遴选出水动力性能最佳的 V 形网板, 并分析其在不同姿态下, 前后倾和内外倾分别为 5°、10°、15°、20°时的水动力系数、周围流场分布和表面压力变化规律, 结果表明：(1)展弦比 λ=0.7、板面夹角 Γ=16°的 V 形网板(13 号网板)的水动力性能最优, 升力系数在冲角为 37.5°时最大, 为 1.482, 冲角为 10°时扩张效率最大。(2)随着冲角的增大, 13 号网板迎流面的压力逐渐增大, 网板迎流面和背流面的速度差亦呈增大趋势。(3) 13 号网板发生不同程度的前后倾或内外倾时, 升力系数降低, 阻力系数则随着倾角的增大而减小。(4)当网板发生内外倾斜时, 随着倾角的增加, 迎流面压力中心向网板前端移动, 网板中心面后涡旋变化不明显; 当网板前后倾斜时, 网板迎流面压力分布变化明显, 即随着倾角的增加, 压力中心分别逐渐向前端上下两侧移动, 并且网板中心面后涡旋逐渐变小。本研究结果可以为预测不同工作姿态网板水动力特性变化, 调整网板稳定性提供科学参考。     

网板水动力性能研究综述

网板是单拖网渔业中实现网具水平扩张的重要渔具构件,网板水动力性能的优劣直接关系到拖网的渔获效率。综述了国内外矩形平面网板、立式曲面网板、立式V型曲面网板和双翼型网板的相关研究进展,分析了这4种网板类型的各自水动力性能,总结了影响其水动力性能的几种主要因素,旨在为旧式网板的改良优化和新型网板的开发研制提供参考。同时,还分别从机翼理论、模型(实物)实验和CFD数值模拟技术3个角度阐明我国网板研究存在的问题和未来发展方向。     

Rare serotype occurrence and PFGE genotypic diversity of Streptococcus agalactiae isolated from tilapia in China

Previously, we reported 10 PEGE types of 85 tilapia Streptococcus agalactiae(GBS), which shifted from Streptococcus iniae in China, by using PEGE method. Presently, larger and more representative tilapia GBS were isolated, for the ?rst time in China, to characterize their serotypes and genetic diversities more precisely than had done before. 168 GBS strains were distributed in ?ve provinces of China, in which Guangdong, Guangxi and Hainan were the major ones, holding36.9%(62/168), 37.5%(63/168) and 19.6%(33/168), respectively. Serotypes, Ia, Ib and III, were observed in these strains and the most predominant one was Ia(95.2%), which mainly distributed in Guangdong, Guangxi and Hainan. Ia initially occurred in 2009, it shoot up to 32.1% in 2010,but decreased to 16.1% in 2011 before went up to 45.2% in 2012. Ib sporadically occurred during2007–2011, III onlyoccurred in 2012. 14 different PFGE types, including 4 new types(N, O,P and Q), were observed, in which B, D, F and G were the predominant types, holding 83.9%(141/168) of the total GBS strains. Ia corresponded to 11 PFGE types(A–H, N–P), in which type D predominated(51%). Ib represented 3 genotypes(I, J and Q) and III harbored only 2genotypes(N and F). Type N and Fsynchronously presented in Ia and III. In summary, the genetic diversity of tilapia GBS varied by serotypes and changed with geographical locations and years.Although Iastillpredominated, new rareserotypeIII alreadyoccurred in China.     

Growth hormone (GH) and reproduction: a review

Interaction between growth and reproduction occurs in many vertebrates and is particularly obvious at certain stages of the life cycle in fish. Endocrine interactions between the gonadotropic axis and the somatotropic axis are described, the potential role of GH being emphasised. A comparative analysis of these phenomena in mammals, amphibians and fish, suggests a specific role of GH in the physiology of puberty, gametogenesis and fertility. It also shows the original contribution made by studies on the fish model in this field of investigations.     

Purification and partial characterization of GtHs (cfLH and cfFSH) from Indian walking catfish (Clarias batrachus) (L.) and development of a homologous ELISA for cfLH

Two gonadotropins (GtH; Qa and Qb) were purified by gel filtration and ion exchange chromatography from the pituitaries of Indian walking catfish (Clarias batrachus). The presence of GtH during purification was assessed by in vitro oocyte maturation and in vivo steroidogenic activity, and their identities were determined by elution profiles, molecular weight, biological activities and yield. The molecular weights of Qa and Qb were 37 and 42 kDa, respectively, and composed of distinct subunits (Qa: 20 and 14 kDa and Qb: 26 and 18 kDa). Polyclonal antibodies raised against Qa immunostained Qa, Qb and pituitary GtH cells. A competitive Qa‐ELISA was developed whose sensitivity was 6.25 ng mL^?1 (1.25 ng well^?1) with intra‐ (3.5%) and inter‐ (12.4%) assay coefficients of variation. Displacement curves parallel to the standard were obtained with plasma and pituitary extracts of catfish, Qb and carp GtHII. The assay was validated by measuring the plasma Qa levels after LHRH treatment and in relation to ovarian growth in the female catfish during different reproductive phases. Based on the results, Qa and Qb corresponded to fish LH and FSH respectively. The findings will increase the knowledge of the mechanisms controlling fish reproduction and identification of sensitive phases in fish in captivity for hormonal manipulation.     

Controlled infection of Poecilia reticulata Peters (guppy) with Tetrahymena by immersion and intraperitoneal injection

Tetrahymena is a protozoan parasite, which infects guppy, Poecilia reticulata Peters, and causes substantial economical losses in commercial farms worldwide. Studies of guppy infected by Tetrahymena require standardized infection protocols. The LD50 for Tetrahymena infection of guppies by intraperitoneal (IP) injection was calibrated, and the level obtained was 946 parasites per fish. Guppy infection with Tetrahymena by immersion, imitating the natural route of infection via the integument, was studied under normal or stress conditions. Exposure to cold and netting (CNI) and to cold only (CI) followed by immersion exposure to 10 000 Tetrahymena per mL resulted in 22.5% and 19.2% mortality, respectively, as compared to 14.2% and 10% in groups that were netted only (NI) or non‐stressed (I). Histopathology revealed that immersion infection resulted in a systemic infection. Lysozyme levels, measured 3 weeks after infection, were significantly higher in the CNI group (288 μg per mg protein) compared with CI‐, NI‐ and I‐treated groups (94.5, 64 and 62.3 μg mg^?1, respectively). There was no evident parasite immobilization activity in body homogenates, suggesting no development of acquired immunity. Re‐infection by IP injection revealed no increase in protection in any of the treatment groups, mortality range of 56.3–75%, higher than in the non‐exposed control (40.6% mortality).     

Evaluation of a Fast Method Based on the Presence of Two Restriction Sites in the Mitochondrial ND5 (mt ND5) Gene for the Identification of Scomber Species

The purpose of this work was to evaluate the suitability of a method based on the presence of two restriction sites (for Hae III and Hindf I) in the mitochondrial NADH dehydrogenase subunit 5 (mt ND5) gene to identify Scomber species. The evaluation was performed on 144 reference and market samples by sequencing of the entire 505-bp fragment of the mt ND5 gene and of a 464-bp fragment of the Kocher fragment of the cytochrome b gene (mt Cytb). Sequence analysis of any of the two fragments allows the identification of each of the four Scomber species, but S. japonicus and S. colias had the same restriction sites at the ND5 amplicon and would not have been differentiated by this analysis. Similarly, loss of the Hae III site in some S. scombrus individuals would have misidentified them as not being Scomber. All the market products were correctly labeled except one acquired in Spain labeled as originating in the Atlantic and containing S. japonicus.     

Imported ornamental fish are colonized with antibiotic‐resistant bacteria

There has been growing concern about the overuse of antibiotics in the ornamental fish industry and its possible effect on the increasing drug resistance in both commensal and pathogenic organisms in these fish. The aim of this study was to carry out an assessment of the diversity of bacteria, including pathogens, in ornamental fish species imported into North America and to assess their antibiotic resistance. Kidney samples were collected from 32 freshwater ornamental fish of various species, which arrived to an importing facility in Portland, Oregon from Colombia, Singapore and Florida. Sixty‐four unique bacterial colonies were isolated and identified by PCR using bacterial 16S primers and DNA sequencing. Multiple isolates were identified as bacteria with potential to cause disease in both fish and humans. The antibiotic resistance profile of each isolate was performed for nine different antibiotics. Among them, cefotaxime (16% resistance among isolates) was the antibiotic associated with more activity, while the least active was tetracycline (77% resistant). Knowing information about the diversity of bacteria in imported ornamental fish, as well as the resistance profiles for the bacteria will be useful in more effectively treating clinical infected fish, and also potential zoonoses in the future.     

Effect of iodophor disinfection of non‐hardened Salmo trutta eggs on their bacterial and fungus load

This study investigated the efficiency of iodophor disinfection (135 ppm active iodine for 15–30 min) of non‐hardened Salmo trutta eggs against different groups of bacteria and against fungus. Egg samples were taken from non‐disinfected and from disinfected eggs, microorganisms were cultured on specific nutrient media and their mass was measured by turbidimetric methods. Bacteria and fungus mass of non‐hardened eggs could be reduced but not eliminated by iodophor disinfection with 135 ppm active iodine for 15 min. The extent of reduction was 47–65% (Experiment 1). The efficiency of disinfection increased with disinfection time as the reduction in bacteria and fungus mass was 40–55% after 15 min and 58–74% after 30 min (Experiment 2). Disinfection efficiency of iodophor solution diluted in water (reduction 49–57%) and of iodophor solution diluted in sodium chloride solution iso‐osmolar to the oocytes (reduction 52–61%) was similar (Experiment 3). The reduction in bacteria and fungus mass was persistent as it was 39–72% lower in embryos deriving from disinfected eggs than in embryos deriving from non‐disinfected ones (Experiment 4). In conclusion, the tested disinfection method is inadequate to eliminate pathogens completely but it could positively influence immune defence of eggs and embryos.     

Nitrogenous waste excretion and accumulation of urea and ammonia inChalcalburnus tarichi (Cyprinidae), endemic to the extremely alkaline Lake Van (Eastern Turkey)

The endemic, anadromous cyprinidChalcalburnus tarichi is the only fish species known to occur in alkaline Lake Van (Eastern Anatolia, Turkey). EightC. tarichi were maintained individually in Lake Van water (17 – 19°C; pH 9.8; 153 mEq·I^–1 total alkalinity; 22 total salinity) and tank water samples analyzed for 24 h in 2 to 4 h intervals. At zero time, < 1µM ammonia was present and urea was undetectable in the tank water; at 24 h, total ammonia and urea made up 114±32 and 35±25µM, respectively. Over the experimental period, ammonia-N and urea-N excretion averaged 1041±494 and 607±169moles·kg^–1 fish·h^–1, respectively. The extent of urea excretion was highly variable between specimens. Uric acid excretion was not detectable.Urea was present at high concentrations in all tissues and plasma (25 – 35moles·g^–1·ml^–1) of freshly caughtC. tarichi; total ammonia content of the tissues was by a factor of 1.9 (liver) to 3.0 (brain) lower. High arginase activity (2.4±0.2 U·min^–1·g^–1) was detected in the liver ofC. tarichi but ornithine carbamoylphosphate transferase, a key enzyme of the ornithine-urea-cycle, was absent. Ureagenesis is likely through degradation of arginine and/or uricolysis. High glutamine synthetase activity (11±0.6 U·min^–1·g^–1) and low ammonia content in brain suggest that, like other teleosts,C. tarichi has an efficient ammonia detoxification in the brain, but in no other tissue.Nitrogenous waste excretion at alkaline pH is discussed. The ability ofC. tarichi to excrete high levels of ammonia at extremely alkaline pH is unique among teleosts studied so far. The mechanism of ammonia excretion under Lake Van conditions remains to be elucidated.