疏目拖网配纲技术

目前拖网渔具正在向大型化、疏目化发展，就山东沿海群众渔业大马力拖网渔船而言，网具目大已由过去的 １０～２０ ｃｍ增大到目前的 １０～１２ ｍ。网具参数改变后，再用传统的配纲方法来进行疏目拖网配纲往往会产生较大误差，而且网目越大计算越不精确。我们在多年的实践探索中，总结了一套比较切合实际的疏目拖网装配方法，介绍如下：１中纲配纲 见图１。 Ｌ＝（ｎ－１）·ｅ·ａ，Ｌ：中纲配纲长度，ｎ：中口门总目数，ｅ：水平缩结系数，ａ：网目大小。 以前拖网网目较小，在配纲中多１目或少１目对配纲误差甚微（误差０．０１％～０…     

变位底拖网

变位底拖网是在不改变现有机帆船双船底拖网网身结构的基础上,采用吊纲绳,侧空纲以及“G”型脱卸钩等装置。使拖网能在一定幅度内有效地调整网位,满足捕捞选择性要求,提高捕捞效果,在拖网捕捞技木方面为国内初次。生产实践证明,变位底拖网在捕捞带鱼,起到了保护资源的作用,既能提高渔获物质量,降低幼鱼的比例,又能减少网具消耗,减轻劳动强度,具有较为显著的经济,生态和社会效益。     

十二、对拖网上网袖配纲计算与上、下纲长度校核

<正> 一、上网袖(上翼网)三段剪裁的配纲计算:根据拖网上纲在作业中比较接近于悬链线形状的特点,自七十年代后期起,国营渔业的机轮对拖网都陆续将上网袖(即上翼网)分三段剪裁。但是,群众渔业的机帆船对拖网尚未普遍采用。     

曳纲长度与网位水层的关系

近几年来，由于拖网操作技术的改进，原来的底拖网网具巳不仅扑捞底层或近底层的鱼类，通过曳纲长度和浮沉力的调整，也可以捕获表层或近表层的鱼类。前些年的秋汛捕虾生产，一些机轮所采用的浮拖网就是底拖网通过曳纲长度和浮沉力配备的调整，把网具从底层提升到表层进行生产作业的。这种浮拖法早在70年代初期辽渔公司有些渔轮在捕起浮的青鱼等鱼类时曾采用过，有的船亦获得数十箱或数百箱的大网头，但仅是偶然的机会。     

绳拖网与普通拖网阻力对比分析↑（*）

本文对目大６ｍ、８ｍ、１０．８ｍ的绳拖网分别与疏目拖网、小目拖网的阻力进行了对比分析。据几顶有代表性的网具统计，绳拖网网口周长比同级渔船使用的疏目拖网增大１．１６～１．４３倍，比小目拖网增大１．８８～２．１６倍。网具阻力分别降低３０％～３４％和４０％～４５％，绳拖网阻力小，为大网快拖、增产增收创造了条件。     

六片式拖网性能的研究

利用１／７比例的网具模型，在拖曳水槽中对六片式拖网进行水槽试验。得出网口高度公式为：Ｈ＝０．１２１ＣＶ＾－０．８１１。网具阻力公式为：Ｒ＝０．０６９ｄ／ａＬＣＶ＾１．５５９。同时得出力纲上装配浮子能提高网口高度３．６％，上中纲与上纲长度之比不能大于０．１４０，上边纲长度可大于相对应的力纲３．３％等设计网具数据。     

底拖网配纲校核法

在分析比较目前中国各地曾使用过的各种底拖网配纲校核方法的基础上，提出了“网翼上、下边缘配纲之差与网盖缩结长度之比”（简称翼纲差比）的新配纲校核方法。翼纲差比较大的拖网，其网口易于升高而沉纲贴底程度较小些；反之，翼纲差比较小的拖网，其网口不易升高而沉纲贴底程度较大些。     

精养中小型水面电拖网的设计试验报告

介绍了精养中、小型水面电拖网网具设计的原理及特点，网具结构和作用；网具的捕捞原理，网具尺度的确定及材料选用和电拖网网具装配工艺等。试捕试验表明，其捕捞性能优良，上层鱼类起捕率达96%以上，中，下层鱼类起捕率超过90％。     

帆带形升浮器

自发明拖网渔法以来，渔民一直在设法使拖网上纲尽可能提高。     

东南太平洋智利竹筴鱼中层拖网捕捞技术

根据2001年7月至2002年8月我国渔船在东南太平洋的智利竹笑鱼(Trachurus murphyi)渔捞记录和现场收集的资料,对中层拖网捕捞技术进行了分析研究,结果表明：(1)中层拖网主要在夜间作业;捕捞水层主要集中在30～80m水深;网位与鱼群的相对位置可分为5种类型,即鱼群在网口的中间、上纲紧贴在鱼群的上部、下纲紧贴在鱼群的下部、鱼群在上纲的上部和鱼群在下纲的下部。(2)鱼群进网数量可根据网位仪映像加以判断。(3)网位(y)与曳纲长度(x)呈线性关系,其回归方程式为：y=0．4427x-36．604。(4)捕捞效率随拖网速度而增加。(5)较高捕捞效率的表层水温指标为11．5～13．5℃。根据研究结果还对我国今后在东南太平洋智利竹笑鱼捕捞技术改进提出合理化建议。     

Physiological and Biochemical Determination of Rainbow Trout,Oncorhynchus mykiss,Semen Quality for Cryopreservation

In rainbow trout, Oncorhynchus mykiss, parameters to determine semen fitness for cryopreservation and quality control of cryopreserved semen were investigated. The following parameters can be used to evaluate semen fitness for cryopreservation as they are statistically significant (P < 0.01) correlated to the post-thaw fertilization rate: motility rate of fresh semen (y = 4.996x - 0.0958x² + 0.0006x³ - 5 1.7363); sperm velocity of fresh semen (y = 6.741x - 0.036x² - 268.37); seminal plasma osmolality (y = 0.539x - 125.59); seminal plasma pH (y = -82.768x + 728.133); seminal plasma triglyceride levels (y = 0.069x + 29.863); seminal plasma ß-D-glucuronidase activity (y = -1.112x + 0.0058x² + 82.229); seminal [lasma lactate dehydrogenase activity (y = -0.096x + 0.00006x² + 583.80); spermatozoan acid phosphatase activity (y = -132.51x + 126.38x² + 66.48); spermatozoan adenylate kinase activity (y = 3.474x + 4.925). Quality of deep-frozen semen can be evaluated by motility parameters (P < 0.01): frozen/thawed semen motility rate and post-thaw fertilization rate: y = 1.943x + 28.002; sperm velocity and post-thaw fertilization rate: y = 0.8812x - 0.0059x² + 24.9686.     

Measuring the height of the fishing line and its effect on shrimp catch and bycatch in an ocean shrimp (Pandalus jordani) trawl

The relationship between fishing line height (FLH), shrimp catch and bycatch in a semi-pelagic ocean shrimp (Pandalus jordani) trawl was investigated using a newly developed recording inclinometer. The inclinometer was effective at measuring FLH and indicating trawl performance deficits. FLH was determined to be stable during a haul and also between hauls within a given footrope and groundline configuration. FLH was readily adjusted with simple modifications to the footrope “dropper” chains. Inclinometer data showed that FLH can be unequal between double-rigged nets of identical configuration. Shrimp catch and the bycatch of flatfish and juvenile rockfish varied inversely with FLH, suggesting FLH can be adjusted to equalize the catch of shrimp, flatfish and juvenile rockfish between two double-rigged shrimp nets.     

Escapement from the main body of the bottom trawl used for the Mediterranean international trawl survey (MEDITS)

Escapement through the body or under the footrope of the sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) was assessed i) by means of visual observations performed with a towed operating vehicle equipped with a high-sensitivity video camera, and ii) by attaching small bags to the outside of the trawl body and under the footrope. Due to the small size of most of the individuals present in the study area and to the towing speed, fish behaviour in front of the trawl could not be frequently observed. In contrast, their behaviour was easily observed inside the net, especially upstream and inside the codend. Some species, such as horse mackerel (Trachurus sp.), showed greater swimming endurance compared with others such as annular seabream (Diplodus annularis). In three fishing trips conducted in different seasons in 1996 and 1997 to obtain data on several species in different areas of the Adriatic, six small net bags were mounted outside the body of the MEDITS trawl to quantify escapement through the trawl belly and under the footrope. Significant escapement of many species occurred in the near-bottom part of the side panels. Norway lobster (Nephrops norvegicus) had the highest rate (64 %), mainly represented by small-size individuals. The escapement of greater forkbeard (Phycis blennoides) was also high (53 %). For hake (Merluccius merluccius), common pandora (Pagellus erythrinus) and poor cod (Trisopterus minutus capelanus), rates ranged from 10 to 16 %. The escapement of red mullet (Mullus barbatus) was very low despite their great abundance. Blue whiting (Micromesistius poutassou) escaped mainly through the mid-height part of the side panel. This great variability of escapement values could affect the proportion rates of the species sampled during a standard survey. Different escape behaviours among size classes were observed for M. poutassou, T. minutus capelanus and P. erythrinus, with smaller individuals tending to escape towards the bottom and larger ones towards the higher parts of the trawl body. In the species where the escape rate was size-dependent, therefore, the size-frequency distributions obtained from the codend catch may not reflect actual size-frequency distributions.     

拖速和曳纲长度对南极磷虾中层拖网网位的影响

利用2015年2—7月随青岛远洋捕捞有限公司南极磷虾(Euphausia superba)大型中层拖网渔船"明开轮"赴南极南舍得兰群岛水域执行农业部南极海洋生物开发利用项目期间收集的网位(D)、网口高度(H)、曳纲投放长度(L)和拖速(V)等数据,分析了拖速和曳纲长度对拖网网位和网口高度的影响。本研究中,网口高度定义为网口上下纲深度之差;网位定义为网口中心位置水深。根据渔船作业习惯和虾群群体特点,曳纲投放长度范围138~258 m,每档间隔20 m。拖速1~3 kn,间隔0.5 kn。结果表明:(1)网口高度变化范围为13.6~24.1 m,网位水深变化范围为50~70 m;(2)作业过程中,南极磷虾拖网网位变化主要由曳纲长度决定,曳纲从138 m开始投放时,每增加20 m,网位平均下降深度约1.9 m,网口高度平均减小1.1 m,曳纲长度对网位和网口高度均产生极为显著的影响(P0.01);(3)拖速由1.0 kn变化至3.0 kn时,网位平均上升速率约2.9 m/kn,网口高度平均减小速率为2 m/kn,平均降低19.8%,拖速对网位和网口高度的影响显著(P0.05);(4)不同曳纲长度时的各拖速区间内的平均网位变化速率呈先减小后逐渐增大的规律。本研究结果不仅可为南极磷虾渔船船长根据虾群的群体大小、水层变化及其与网具的位置关系,适时调整曳纲长度和拖速,使网位到达预设水层,实现瞄准捕捞提供参考,还可为研究南极磷虾拖网网具性能的优化以及南极磷虾拖网网具设计的改进提供基础资料。     

Comparing and modifying penaeid beam and otter trawls to improve ecological efficiencies

In an attempt to improve the selectivity and engineering performances of generic penaeid trawls, three established and one novel spreading‐mechanism configurations were assessed: otter boards attached (1) with and (2) without 3.15‐m sweeps to a 7.35‐m headline trawl, and a beam rigged directly to a 9.19‐m trawl (3) with and (4) without a horizontal wire and plastic streamers. Despite more surface area (7.5 vs 6.0 m²), both beam‐trawl configurations had significantly lower drag than the otter trawls (≤30%). When catches were standardised to per ha, the otter trawl with sweeps retained significantly more (1.3–2.4 times) school prawns, Metapenaeus macleayi (Haswell), than the other three configurations. Within systems, removing sweeps or adding a horizontal wire significantly reduced the unwanted catches of a key teleost (southern herring, Herklotsichthys castelnaui Ogilby) by 41 and 48%. The results illustrate the utility of simple anterior modifications for independently addressing penaeid‐trawling environmental issues.     

青鱼消化器官数量性状胚后发育规律

采用显微解剖和测量、光镜和扫描电镜观察方法，系统观测全长为５．６～３３０．０ｍｍ的青鱼标本３７０尾，描述了鳃耙、咽齿、角质垫和肠等消化器官数量性状在胚后发育过程中的变化规律；论述了青鱼的摄食特性、消化器官数量性状胚后发育的阶段性及其相关性、消化器官数量性状发育与食性转化，为制订培育青鱼苗种和饲养成鱼的生物学技术提供了可靠依据     

不同贝龄栉孔扇贝数量性状的相关性和通径分析

为深入了解栉孔扇贝形态性状与湿重之间的关系,为栉孔扇贝选育工作中亲贝的挑选提供策略,本研究使用来自同一家系的栉孔扇贝子代324只一龄个体以及生长到二龄的230只个体的性状数据进行通径分析。性状数据包括壳长(x_1/cm),壳高(x_2/cm),壳宽(x_3/cm),湿重(y/g)。结果显示,所有形态性状和湿重之间的相关系数均达到极显著水平。其中与一龄贝湿重相关系数最大的是壳长,为0.939,与二龄贝湿重相关系数最大的是壳高,为0.808。通径分析结果显示,壳长对一龄贝湿重的直接影响最大(0.532),壳高对一龄贝湿重的直接影响最小(0.163)。壳高对二龄贝湿重的直接影响最大(0.451),壳长对二龄贝湿重的直接影响最小(0.191),决定系数与以上通径分析结果的变化趋势一致。利用多元回归的方法构建了一龄贝和二龄贝形态性状与湿重间的回归方程,一龄贝:y=–10.527+0.287x_1+0.087x_2+0.409x_3,R~2=0.926;二龄贝:y=–68.609+0.254x_1+0.719x_2+2.008x_3,R~2=0.830。本研究结果为栉孔扇贝种贝的挑选提供了理论依据。     

大网目底中层拖网模型试验研究

利用1:22.82比例的2张网具模型,在拖曳水槽中进行底中层拖网的网具性能测试,得出网具阻力公式为:F=0.121(d/a)LCV~(1.62),网口高度的公式为:H=0.225CV~(-1.316),2张网具的作业性能良好,GM_2的垂直张开性能优良,拖速3节时的垂直扩张系数已接近7％,能耗系数在拖速3节时为0.2kw.h/10~4m~3,在同类渔具中较优;GM_1网的能耗系数比GM_2网低,在拖速3节时低于9％左右,作为中层拖网时的总体性能优良。     

Protein requirements of grass carp fry (Ctenopharyngodon idella Val.)

The study was aimed at determining the optimal level of protein in a casein diet for grass carp. There was a linear relationship between the percentage of protein in the diet and the increase in fish protein and weight up to optimal levels of 41 and 43%, respectively. No further increase in fish protein or weight was noted with diets containing up to 64% of protein. However, if the optimal level was defined by the parabolic curve with the formula y = 36.21 + 6.238x ? 0.0593x², it would equal 52.6 ± 1.93%. Net protein utilization (NPU) values for experimental diets were obtained using a formula which took the maintenance nitrogen metabolism on a non-protein diet into consideration. This NPU formula was related to the length of the experiment, difference in the weight of fish at the beginning of the experiment, and growth of fish fed protein diets. Both protein efficiency ratio (PER) and NPU decreased with the increase in protein content of the diets according to the formulae y = 1.966?0.018x and $\text{y = 40.8?0.327x +}\text{302.6}\text{x}$, respectively.     

拖网囊网网目及其对东海带鱼选择性的研究

本文介绍了东、黄海拖网囊网网目的套网系列试验结果，指出当带鱼的刺鱼体周相当于网目内周时，其体长一般大于这种网目对带鱼的50％选择体长。文中比较了按照刺鱼体周求算网目内径同用50％选择体长决定网目内径的不同之处。根据网目内径与刺鱼体长的相关式，提出保护东海带鱼资源的拖网囊网最小网目内径为56毫米，并依据网目的选择性及带鱼的生物学资料，讨论了采用这一网目尺寸的可行性。