Habitat associations of upper Volga river fishes: Effects of reservoirs

Habitat associations of upper Volga river fishes are defined within a cycle of spawning, feeding and overwintering migrations. The migration cycles of resident riverine fishes are categorized as obligate rheophils, limno-rheophils and limnophils. Forty-four fish species in 14 families occurred in the upper Volga River before regulation. Four mainstem reservoirs were constructed on the upper Volga between 1937 and 1957: Ivankovo, Uglich, Rybinsk and Gorky. They are maintained in a stage of delayed and sustained annual flood pulse. Additional impacts of reservoir construction include the creation of a new pelagic habitat, replacement of floodplains by lacustrine littoral and sublittoral habitats, creation of a complex bathyal habitat from former river channels and replacement of riverine flow patterns by pelagic water mass circulations. Populations of rheophilic species declined, while a new pelagophilic fish guild developed. Forty-six fish species are now present; seven species were lost and nine introduced after impoundment. Spawning, feeding and wintering habitats are outlined for reservoir guilds. Ichthyomass increased three to four times following reservoir construction and commercial fish harvest from Rybinsk Reservoir between 1945 and 1992 ranged from 2220 to 4304 t/y. Reservoirs of the upper Volga have limited bioproductivity due to a deficiency and uneven distribution of reproductive habitats, decreasing bottom irregularity, seasonal anomalies of flooding and draining of the littoral and sublittoral and underestimating the importance of tributaries. Lack of littoral reproductive habitat can be remedied by increasing the area of protected littoral through the construction of chains of small islands, diking and reclamation of bogged areas. Improved reproduction of migrating local stocks can be achieved by removing sand bars across tributary mouths, construction of artificial spawning grounds and restoration and preservation of preferred habitats in the main channel.     

Catches of Larval Rainbow Smelt (Osmerus Mordax) and Alewife (Alosa Pseudoharengus) in Plankton Nets of Different Mesh Sizes

Four 0.5-m plankton nets (one each of 0.355-, 0.450-, 0.560-, and 0.750-mm mesh) were used to collect larvae of the alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) in northwestern Lake Huron and the St. Marys River. The number of larvae collected varied inversely with mesh size and the average length of larvae varied directly with mesh size. Numbers of each species caught in 0.355- and 0.450-mm mesh nets were significantly greater (P < 0.01) than the numbers caught in 0.560- and 0.750-mm mesh nets. Numbers of alewives caught were significantly greater (P < 0.01) in the 0.355- than in the 0.450-mm mesh, but numbers of rainbow smelt caught in the two meshes were about equal. Between the two larger-mesh nets, numbers of each species caught did not differ significantly. Nets with mesh larger than 0.355 mm were less effective at catching recently hatched larvae, and this reduced effectiveness accounted wholly for the smaller numbers caught in the 0.450-mm mesh net. Smaller numbers were caught in the 0.560- and 0.750-mm mesh nets not only because they caught fewer recently hatched larvae but also because they failed to retain older, larger larvae. Information on the effect of mesh size and towing speed on catches of larvae is important for making accurate estimates of larval densities.     

Estimating Larval Fish Abundances from Plankton Net Catches in Long Point Bay,Lake Erie,in 1971–78

Larval fish were sampled in Long Point Bay each summer in 1971–78 by towing ½– and 1-m diameter plankton nets at about 1 m/s. We report on the analysis of 2,576 tows, giving detailed consideration to sampling problems and statistical methods. The most common larvae were rainbow smelt (Osmerus mordax), caught in about 50% of the tows, and yellow perch (perca flavescens), clupeids, and cyprinids, caught in about 10 to 20% of the tows. Most of the data contained too high proportions of zero catches to be transformed to approximately normal distribution, and were therefore analyzed using the log-linear model rather than by analysis of variance. Except for cyprinids, larval fish seemed to be scarce in surface waters during the day. Small (4 to 10 mm long) smelt and perch larvae were caught more frequently in 526– than in 782–μm mesh nets. Very few perch and cyprinid larvae longer than 10 mm were ever caught. This, and a more rapid decline of daytime than nighttime catches of larval smelt through the mid-summer, suggests that the nets were avoided by at least the larger larvae. If avoidance of sampling gear is substantial, larval fish abundances may be overestimated in years of slow growth when the larvae remain catchable longer. We saw no evidence that the recent industrial development at Nanticoke, Ontario, has affected larval fish abundances so far. As the annual mean densities of larval fish varied 15-fold or more, it would require several years of observation to detect any but drastic future change from the current levels of abundance.     

超高效液相色谱-串联质谱法测定腌鱼中氟虫腈及其代谢物的残留

本文采用超高效液相色谱串联质谱法测定了腌鱼中氟虫腈及其代谢物氟虫腈砜、氟虫腈亚砜、氟甲腈。腌鱼样品经乙腈提取、盐析和吸附剂净化,以0.1%甲酸的甲醇溶液和0.1%甲酸的5 mmoL·L^-1乙酸铵溶液为淋洗液在BEH C18色谱柱梯度洗脱,电喷雾负离子多反应监测(Multiple Reaction Monitoring,MRM)模式检测。结果表明,氟虫腈及其代谢物在0.25～10.0 ng·mL^-1呈良好的线性关系,相关系数均大于0.999;在1.0～10.0μg·kg^-1添加范围内,氟虫腈及其代谢物的回收率为91.79%～109.84%,相对标准偏差为0.91%～3.39%(n=6);该方法检出限和定量限分别为0.2～0.4μg·kg^-1和0.8～1.2μg·kg^-1。本方法操作简单、灵敏,可同时测定腌鱼中氟虫腈及其代谢物的残留量,为其日常监管提供技术参考。     

观赏渔业:部市型水产业的新亮点--上海发展观赏渔业的思考和建议

观赏渔业是都市型水产业发展的经济增长点，本文从观赏鱼需求和供应两方面分析了发展观赏渔业的潜力和存在的问题，在发展观赏渔业的理论和实践措施方面作了积极的探索。     

Regime Shifts in the Fish Meal/Soybean Meal Price Ratio

Aquaculture growth has led to worries about overfishing and reduction in wild‐caught food fish supply because of increased demand for fish meal. As such, the price ratio between fish meal and soybean meal has received much attention as an indicator of changing market conditions. In recent years, the price ratio between these two commodities has become more volatile. Several authors have suggested that the traditional relationship between fish meal and soybean meal has broken down and that this is evidence of increased demand pressure on fish meal. In this article, we investigate the hypothesis that there are two regimes for the relative price between fish meal and soybean meal. The empirical results support this hypothesis, with the low‐price regime representing the traditional stable relative price. The continued linkages between the fish meal and the soybean meal markets indicate that aquaculture is reducing its dependency on marine proteins in favour of vegetable proteins.     

The impact of increasing non-agricultural market access on EU demand for imported fish: implications for Lake Victoria chilled fillet exports

Import demand functions for origin-specific chilled fish filletsto the EU using a Rotterdam-type production model are estimated.Results are used to project the impact of the EU expanding marketaccess to non-African countries. The preference erosion argumentsuggests that the lower tariffs will erode the competitive positionof African countries; however, when the total impact of pricesis considered, expanding preferential access may result in increasedimports from African countries. If tariffs are reduced to zero,the total EU imports are projected to increase by 4.1 per centresulting in a 2.2 per cent increase in chilled fillet importsfrom Lake Victoria.     

Climate change adaptation actions by fish farmers: evidence from the Niger Delta Region of Nigeria

This paper examined climate change adaptation strategies in fish farming and the effect of such methods on the profit of fish farmers in the Niger Delta region of Nigeria, Africa’s most populous country. Using cross‐sectional data obtained from 420 fish farmers from the region and applying multivariate probit and instrumental variable regressions, the study found that fish farmers have adopted a broad range of strategies to address climate risk and that these have significantly increased farmers’ profit. Our findings indicated important relationships between certain farm, socio‐economic and institutional characteristics and the adaptation actions. The study provides useful insight into factors that potentially encourage the adoption of livelihood‐enhancing climate risk adaptation strategies by fish farmers in the Niger Delta region and similar contexts.     

土豆红豆鱼香肠的研制

鱼香肠是以鱼肉为主要原料灌制的香肠。它营养丰富、味道鲜美、风味独特,深受广大消费者喜爱,尤其是老人和儿童。鱼香肠的优点是有外包衣(畜肠衣或塑肠衣)使鱼肉与外界隔绝,流通方便,卫生条件较好,加工后可长期保存。本文通过正交实验,探讨土豆和红豆添加量对鱼肉香肠感官质量的影响,逐步确定土豆和红豆的最优添加量,最终确定了新型鱼香肠最优配比为:以鱼肉质量计,土豆添加量:37%,红豆添加量:38%,畜肉添加量:15%,板油添加量:7.5%,淀粉添加量:5.6%,精盐添加量:2.25%,咖喱粉添加量:0.43%,胡椒粉添加量:0.06%,味精添加量:0.2%。     

基于社会化招聘成熟度模型的“投名状鱼塘”建设

F公司把社会化招聘作为树立最佳雇主品牌形象(EVP)以及建设员工价值体系(EVP)的重要途径,通过社会化招聘达到提升公司内外忠诚度的目的。本研究以中国背景下的外资企业F公司为例,探讨了复杂多变环境下F公司社会化招聘体系的建立以及建立过程中遇到的问题。