Modelling changes in the length–frequency distributions of fish larvae using field estimates of predator abundance and size distributions

The goal of this study is to determine if an individual-based size-dependent model can realistically simulate changes in the length–frequency distributions of several species of fish larvae collected in Conception Bay in 1993 and 1994, using field estimations of growth and predator abundance. We first model the length–frequency distribution of field samples with the best possible estimates of mean growth rate. Then, we add predation mortality given the characteristics of the predator community observed during our surveys, which was composed of macrozooplankton and adult capelin. The larval fish community is generally not affected by predation by macrozooplankton, as the average instantaneous mortality rate predicted by the model was 0.004 day^–1. Fish larvae appear to be more vulnerable to predation by the population of adult capelin. We estimate that an abundance of adult capelin ranging between 0.2 and 1.0 individuals per 1000 m^–3 may have a substantial impact on the larval fish community. The predictions of an individual-based model are directly related to the accuracy of estimates of the mean growth rates of the larval fish cohorts. We find that it is difficult to differentiate size-selective removal of individuals from random selection by analysing changes of the length–frequency distributions of the larval fish community.     

非独立悬架和独立悬架三轮汽车特性计算与比较

计算了非独立钢板弹簧后悬架和单横摆臂式独立后悬架三轮汽车的平顺性和操纵稳定性指标,通过比较可见,具有单横摆独立后悬架的三轮汽车有较好的平顺性和操纵稳定性,并建立了计算三轮汽车车架侧倾角的公式。     

Growth rates and survival of western rock lobster (Panulirus cygnus) at two temperatures (ambient and 23 °C) and two feeding frequencies

Wild caught post-pueruli, year one and year two post settlement juvenile western rock lobster, Panulirus cygnus, were held at ambient temperatures (15.6 °C to 23.1 °C; mean 19.0 ± 0.07 °C) or at 23 °C, and fed the same ration of a formulated pellet diet either once per night, or 3 times per night, over 12 months, to determine whether elevated temperatures and multiple feeds per night would stimulate growth through increased metabolism and feed utilisation without significant negative impacts on survival. Survival of post-pueruli (mean 63%) did not differ between ambient and 23 °C. Survival of year 1 and 2 juveniles was higher at ambient temperatures (p < 0.01 ambient: year 1 juveniles, 68%; year 2 juveniles, 88%; 23 °C: 57% and 74%, respectively). Feeding frequency did not affect survival of post-pueruli and year 2 juveniles (mean 63%, 81% respectively), but survival was 9% higher for year 1 juveniles fed three times per night (58% versus 67%; p < 0.01). All lobsters grew faster at 23 °C than at ambient temperatures (p < 0.05), with the growth of post-pueruli almost doubled at 23 °C (weight gain at 23 °C versus ambient: post-pueruli, 18 438 % versus 9 915 %; year 1 juveniles 259% versus 165%; year 2 juveniles 23% versus 21%). Feed frequency did not influence the growth of year 1 and 2 juveniles. However, there was an interaction effect of temperature and feed frequency on post-pueruli where weight and carapace length were significantly higher at ambient temperatures when post-pueruli were fed three times a day, whereas at 23 °C weight and carapace length were significantly greater when fed once per day (p < 0.05). Feed intake (g pellet dry matter lobster^− 1 day^− 1) of pellet was higher at 23 °C for all lobsters (p < 0.05), but was the same between lobsters fed 3 times per night versus once per night. This study has shown that increasing temperatures to 23 °C significantly improved the growth of P. cygnus post-pueruli without any adverse effects on survival. The faster growth rates exhibited by year 1 and 2 juveniles at 23 °C may potentially offset their lower survival by significantly reducing culture period. There is no benefit of feeding P. cygnus multiple times at night in terms of growth and survival. The implications for P. cygnus culture are that temperatures should be maintained close to 23 °C during the entire growout period, with due care taken to minimise mortalities through adequate provision of food and shelter. Feeding P. cygnus once daily to excess just prior to dusk to co-incide with nocturnal feeding behaviour is recommended.     

Effects of dietary macronutrient level and feeding frequency on growth and body composition of juvenile rockfish (Sebastes schlegeli)

An 8-week feeding experiment was conducted to investigate the effects of different dietary macronutrient level and feeding frequency on the growth, feed utilization, and body composition of juvenile rockfish. Triplicate groups of fish (body weight of 4.1 g) were fed the experimental diets containing either high levels of carbohydrate (HC, 35%), lipid (HL, 13%), or protein (HP, 55%) at different feeding frequencies (twice daily, once daily, and once every 2 days). Weight gain was affected by feeding frequency but not by dietary composition. Weight gain of fish fed the diets once every 2 days was significantly (P < 0.05) lower than that of other groups. Daily feed intake and energy intake were affected by both dietary composition and feeding frequency. Daily feed intake of fish fed the HC diet was significantly (P < 0.05) higher than that of fish fed the HL and HP diets at the same feeding frequency. Feed efficiency and protein efficiency ratio were affected by both dietary composition and feeding frequency and decreased with increasing feeding frequency in the same dietary composition. Feed efficiency and protein efficiency ratio of fish fed the HC diet were significantly (P < 0.05) lower than those of fish fed the HL diet at the same feeding frequency. Whole-body lipid content of fish fed the HL diet was significantly (P < 0.05) higher than that of fish fed the HC and HP diets at the same feeding frequency. These results indicate that an increase of dietary lipid level compared with dietary carbohydrate level may have the advantage of a protein-sparing effect at same feeding frequency, and a once-daily feeding regime is more effective than twice daily or one feeding every 2 days to improve growth performance of juvenile rockfish grown from 4 to 21 g.     

中国主栽水稻品种微卫星标记数据库的初步构建

以前期筛选的微卫星标记为基础,并在4个染色体上增加新标记,进一步检测了63个主栽常规稻品种和杂交稻亲本,推荐了24个微卫星标记（每条染色体2个）作为水稻品种鉴别的标记;除了63个常规稻品种和杂交稻亲本外,这24个标记还应用于检测41个主栽杂交稻组合,并确定了各个标记在试验材料中检测到的等位基因类型。通过杂交稻组合与其亲本的标记匹配性检验,确认了杂交稻母本的高真实性,提高了恢复系数据的可靠性,剔除了1个假杂交稻,建立了103个水稻材料×24个标记的主栽水稻品种微卫星标记数据库,并分析了数据库中各个标记、各组材料的多态性表现。此外,还讨论了材料真实性和典型性对数据库构建的影响,提出了水稻品种间差异判别标准的建议及其应用风险和解决途径。     

牛瘤胃胃电频谱分析中窗函数的选择

采用三种常用的窗口函数,对牛瘤胃４ 种生理状态下胃电（峰电位和慢电位）的频谱进行了分析比较,得出了不同窗函数下频谱中幅值的特性,并分析确定了作者课题组频谱分析时的窗口函数——汉宁窗。     

中国稻瘟病菌种群分布及优势生理小种的研究进展

 着重概述了中国主要水稻产区稻瘟病菌的种群分布与生理小种的组成状况。目前东北稻区稻瘟菌主要种群为ZF、ZD、ZE和ZA,出现频率分别达到23.2%、22.2%、15.6%、12.3%。西南稻区以强致病力菌株ZA和ZB为主,四川省内ZB种群频率高达53%,ZA为22.3%;贵州省的优势种群为ZB、ZA和ZG,出现频率分别为41.4%、18.5%和10.7%。华南稻区主要种群为ZB和ZC,出现频率分别为28.0%和37.0%。华北稻区以致病力较弱的ZE、ZF和ZG群体为主,出现频率分别达到21.5%、22.1%和44.3%。华东稻区主要种群为ZB、ZG、ZC和ZA,出现频率分别为43.3%、25.0%、13.9%和123%。华中稻区主要是ZA、ZB、ZE和ZC,出现频率分别为34.9%、28.8%、21.4%和14.1%。西北地区水稻种植较少,但以致病力强的ZA和ZB群为优势种群。     

投喂频率对龙虎斑幼鱼生长和饵料利用的影响

在室内车间采用4种不同的投喂频率养殖龙虎斑幼鱼（47．6±5．2 g）,分析和比较不同投喂频率对其生长和饵料利用的影响。试验设S1、S2、S3、S4共4组,分别按照1、2、3、4次/d进行投喂,共进行60 d。结果显示：（1）投喂频率显著影响龙虎斑幼鱼的生长（P＜0．05）。 S1的平均体质量显著低于S2、S3、S4（P＜0．05）,为149．7 g;S2、S3、S4组间差异不显著（P＞0．05）,S4最大（168．7 g）,其次为S3（168．0 g）和S2（162．2 g）;S1日增体质量、增重率、特定生长率显著小于S2、S3、S4（P＜0．05）,分别为1．68 g,204．83％,1．86％/d,S2、S3、S4组间差异不显著（P＞0．05）,S2特定生长率最大,为2．12％/d;S2的体质量回归方程斜率最大,为1．915,S1最小,为1．532。（2）投喂频率对龙虎斑幼鱼的饵料利用影响显著（P＜0．05）。 S2的摄食率和饵料系数显著小于S1、S3、S4（P＜0．05）,分别为1．31％/d、0．70;S4摄食率最大,为1．64％/d;S1、S3、S4组间饵料系数差异不显著（P＞0．05）,分别为0．88、0．84、0．88。因此,综合养殖效果和劳动强度考虑,S2的投喂频率最适合龙虎斑的养殖,建议在龙虎斑的养殖生产中,最适宜的投喂频率为2次/d。     

Relationship Between Dietary Protein Source and Feeding Frequency During Feeding Nile Tilapia,Oreochromis niloticus (L.) Cultured in Concrete Tanks

ABSTRACT

A 24-week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 50.87 ± 6.03 g and 14.4 ± 0.45 cm, respectively, to examine the effect of two protein sources and two feeding frequencies on growth performance, production traits, and body composition. Twelve 4 m³ concrete tanks (2 × 2 × 1.25 m, long, width, and height) were each stocked with 100 fish and fed diets containing either fish meal protein or soybean meal protein at two feeding frequency of two times daily or four times daily (2 × 2 × 3 factorial experiment). The results revealed that there was no significant effect of dietary protein sources on growth rate, whereas there was a significant increase in growth rate with increasing feeding frequency (P < 0.05). The same trend was also observed for mean body weight (g), production rate (kg/m3), specific growth rate (SGR % day^?1). The best final mean body weight (g), specific growth rate (SGR % day^?1), and production rate (kg/m3) were recorded in groups of fish fed with feeding frequency four times daily. Whole fish moisture, protein, fat, and ash contents were significantly influenced (P ≤ 0.05) by protein sources and feeding frequency, except protein not influenced with feeding frequency. Energy was significantly (P < 0.05) influenced by feeding frequency, but not by dietary protein sources. Economic evaluation indicated that soybean meal (Diet B) at four times feeding daily was the most cost-effective and affordable feed strategy for farmers. We conclude that a soybean diet fed four times daily is recommended for adult Nile tilapia reared in concrete tanks.     

变频调速装置在给水系统中的应用分析

分析讨论了工业企业给水系统的特点和当前常用的给水系统调节方式和优缺点及变频调速装置的节能原理,指出变频调速装置应用于给水系统是最为节能的运行方式.