隔板长度对紧凑型高速磁力泵水力特性及叶轮径向力的影响

为探究蜗壳内隔板长度对紧凑型高速磁力泵外特性与叶轮径向力的影响,根据蜗壳型式及隔板长度的不同提出6种蜗壳方案.设单蜗壳为方案一,其余双蜗壳方案根据隔板长度从小到大依次设为方案二至方案六.采用ANSYS-CFX软件对不同工况下(0.8Q_d,1.0Q_d,1.2Q_d)各蜗壳方案泵内流场进行数值模拟,得到不同蜗壳方案的泵中心面静压分布云图,并进行径向力分析.采用方案四蜗壳作为泵实型样机进行试验,将试验值与计算结果进行对比.研究结果表明:相较于无隔板的单蜗壳泵,采用有隔板的双蜗壳泵有利于平衡叶轮径向力,在额定流量下单蜗壳在x,y方向的径向力最大分量分别为151.2,149.7 N,是双蜗壳方案四的1.5倍;随着隔板长度的增大,泵的扬程与效率均逐渐提高,叶轮径向力不断减小,3种工况下扬程的模拟值与试验值偏差均小于3.0%;试验表明数值计算结果具有可信性,研究结果可为紧凑型高速磁力泵在提高水力性能以及平衡叶轮径向力方面提供一定参考.     

Circadian heart rate changes and light-dependence in the Mediterranean seabream Sparus aurata

Despite the abundant literature on circadian heart rate rhythms in fish, few studies have attempted to elucidate if such pattern is endogenous or if it is modulated by environmental cues. In this study, heart rates were continuously recorded in Sparus aurata acclimated to different light regimes (normal or shifted LD 12:12 cycle and a pulsed 0.75:0.75 LD cycle) to investigate the endogenous nature and the role of light on the circadian pattern of heart rate. Under LD 12:12, the daily pattern of heart rate showed higher values at night and lower rates during the day (average amplitude of the heart rate change of 10.6 ± 5.7 beats min^–1). The circadian pattern was maintained in animals under constant light but the amplitude was decreased (2.4 ± 1.1 beats min^–1). Light masks the expression of the rhythm because under a pulsed LD cycle, heart rate tracks the pulsed LD phases, increasing during the dark phase and decreasing during the light phase. Besides the ultradian pattern imposed, an underlying circadian rhythm was detected, which indicates that the rhythm is endogenous. However, the strong link between heart rate and light obtained under pulsed LD cycles suggest the timing mechanism to be mostly based on external light reception.     

不同光照条件对浮游植物生物量与多样性的影响

通过构建光照强度与浮游植物生物量和群落结构特征参数的关系曲线,为三峡水库水华预测预报模型的构建提供基础数据,同时也为水库调度的方案提供理论依据。基于三峡水库野外原位观测数据的分析结果,针对性设计不同梯度光照强度下浮游植物的生长演替规律室内控制实验。结果表明:(1)光照是影响浮游植物生物量和多样性的关键要素,光照强度0~4 500 lx,浮游植物的生物量随着光照强度的增加而增加,在光照强度为4 500 lx时,浮游植物生物量达到最大,但光强超过4 500 lx之后,浮游植物的生物量随着光照强度的增加而减少;光照强度0~1 500 lx,浮游植物群落多样性随着光强的增加而增加,在光照强度为1 500 lx时,浮游植物群落多样性达到最大;光照强度1 500~4 500 lx,浮游植物群落多样性随着光照强度的增加而减少;当光强超过4 500 lx,浮游植物群落多样性随着光照强度的增加而增加;(2)从制定三峡水库生态调度方案的角度来看,当光照强度在1 500 lx时,浮游植物生物量达到最低,此时其群落多样性达到最大,为最佳的调度方案光照参数;(3)浮游植物生物量(y)与光照强度(x)的关系为:y=2×10~(-8)x~3-5×10~(-4)x~2+3.1923x-122.92(R~2=0.934,P0.01),两者极显著相关;多样性指数(y)与光照强度(x)的关系式为:y=2×10~(-12)x~3-3×10~(-8)x~2+10~(-4)x+0.3266(R~2=0.554,P0.01),两者极显著相关。     

水体光照强度的变化对浮游甲壳动物群落结构的影响

近年来,我国淡水湖泊富营养化现象日益严重,藻类大量生长导致水体光照强度减弱,水生植物严重衰退。为了解水体光照强度减弱对生活在沿岸带草丛中的浮游甲壳动物分布情况的影响,本研究于2015年5月至2015年11月在水族箱中通过移植苦草并覆盖不同层黑色遮阳布来建立4个光照梯度（L1- L4）,其透光率分别是40.5%、17.1%、7.1%和2.8%,来模拟自然条件下沿岸带浮游甲壳动物群落对低光压力的响应,分析了水体理化指标、苦草和浮游甲壳动物群落结构变化。结果表明：（1）从不同的光照处理来看,浮游甲壳动物生物量随光照强度减弱而减少,其平均值分别是1.27 mg/L、0.99 mg/L、0.95 mg/L和0.45 mg/L,丰度和多样性也随光照强度减弱逐渐降低;（2）与其他3个处理组相比,L4组中除了锯缘真剑水蚤相对生物量百分比从5%升高到25%,其他种类都有所下降,其中晶莹仙达溞从50%降至9%;（3）浮游甲壳动物的平均生物量在秋季（1.28 mg/L）大于夏季（0.54 mg/L）,而夏季（83.79 ind./L）平均丰度大于秋季（53.59 ind./L）。统计分析表明浮游甲壳动物群落结构变化与光照强度和苦草生长引起的水体理化的变化显著正相关,主要是溶解氧和pH值。     

Tailoring codend mesh size to improve the size selectivity of undifferentiated trawl species

Tiger flathead, Neoplatycephalus richardsoni (Castelnau), and sand flathead, Platycephalus bassensis Cuvier, are undifferentiated and managed with a common legal minimum length (LML). The Commonwealth Trawl Sector (CTS) and the Tasmanian Danish‐seine fishery (TDSF) use a minimum codend mesh sizes of 90 and 70 mm, respectively. The codend mesh size should be tailored to the LML, which is based on the length of first maturity of females (M₅₀). This study found the length–girth relationship of N. richardsoni and P. bassensis was not significantly different. Using the covered codend method, these two species had 50% retention lengths (L₅₀) of 294 ± 2 and 307 ± 3 mm, in 70‐mm and 90‐mm codends, respectively. L₅₀ estimates for mesh sizes from this study and others produced a curvilinear relationship: y = 120 ln(x) ? 214, with an r² of 0.8504. The size at maturity (M₅₀) for female N. richardsoni was 337 mm, which is larger than the estimate for female P. bassensis (247 mm). There is a mismatch between the estimates of L_50, the estimates of M₅₀ and the LMLs in each fishery, leading to suboptimal exploitation of female Platycephalus. The model produced in this paper recommends a codend mesh size of 98 mm for both fisheries to exploit Platycephalus species sustainably.     

Effect of LED light quality on the phototaxis and locomotion behaviour of Haliotis discus hannai

Abalones were reared in a laboratory to determine the percentage response rate, response time, average crawling speed and the time taken to recover an upright posture under nine light‐emitting diode light quality treatments (red, orange, yellow, green, cyan, blue, purple, white and grey) and a dark environment. Animals were placed in the centre of an experimental device, and the tropism of each animal was continuously monitored by video. The highest percentage response rate (80% in dark adapted abalones, 60% in light adapted abalones) was observed in the dark environment, followed by red and orange light (27% and 30% in dark adapted abalones, respectively, 22% and 24% in light adapted abalones). Two induction materials (substrate and brown algae Laminaria japonica) were used to assess the effect of light quality on the tropism of abalones, with the highest percentage response rate (76% in the L. japonica treatment, 22% in the substrate treatment) also observed in the dark environment, followed by red and orange light (both 25% in the L. japonica treatment, and 26% and 32%, respectively, in the substrate treatment). The tropism order of the abalones under dark, red, orange and yellow light was as follows: dark > orange > red, yellow, but fewer abalones chose to stay in blue, green, cyan and purple light. The response time (about 700 s) in the dark environment was significantly longer than for the other light quality treatments. Compared with the average crawling speed in the other light quality treatments, abalones were relatively slower (about 3.8 mm s^?1) in red and orange light, and the dark environment. The mean time required for the recovery of an upright posture in red light and the dark environment was longer than in the other light quality treatments, with the average recovery time reaching a maximum of 60 s in the dark environment. The results demonstrate the phototaxis and locomotion behaviour of abalones, as well as confirming the necessity of a dark, orange or red environment for their management and aquaculture.     

光强、温度和N/P比对坛紫菜叶状体单性生殖发生的影响

为探究培养条件对坛紫菜叶状体生长和单性生殖发生的影响,研究了不同光强、温度和N/P比下坛紫菜叶状体的生长及单性生殖发生的特点。结果显示,当光强为10～40μmol/(m2·s)时,藻体生长缓慢、成熟晚、单性生殖发生晚;光强增至60～80μmol/(m2·s)时,藻体生长加快,成熟和单性生殖发生同时提前。温度为17～20°C时,藻体生长慢、成熟晚、单性生殖发生推迟;23°C时藻体生长最快;而29°C组的藻体虽然生长受到抑制,但藻体成熟和单性生殖发生得到促进。N/P比为16∶1处理组的叶状体比其他处理组(1∶1、4∶1、32∶1和64∶1)均生长变快,N/P比为64∶1时叶状体生长最慢,但易成熟、易发生单性生殖。因此,在高光强、高温和高N/P比下,藻体成熟和单性生殖发生均提早,说明这些因素对坛紫菜叶状体单性生殖的发生有重要影响。     

Influence of light intensity on biofilm formation and the performance of pink shrimp Farfantepenaeus paulensis juveniles reared in cages

A reduction in light intensity may increase shrimp activity, although it may also negatively affect the development of photoautotrophic organisms present in biofilm, an important natural food source for shrimp. This experiment evaluated the influence of light intensity on biofilm development and on the growth of cultured Farfantepenaeus paulensis juveniles. Six cages were deployed in a shrimp culture pond and stocked with 60 juveniles (0.72 ± 0.03 g). Three cages were randomly chosen and covered with five layers of polyamide net to reduce light incidence (shaded treatment), while the other three cages were not covered (control treatment). Biofilm chlorophyll a and microorganism abundance, as well as shrimp growth, were monitored during the experiment. Chlorophyll a concentration and the abundance of bacteria and flagellates were significantly lower in the shaded treatment (P<0.05). After 75 rearing days, shrimp stocked in control treatment achieved significantly higher (5.98 g) (P<0.05) mean weight than shrimp reared in shaded treatment cages (5.13 g). Similarly, the biomass produced was also significantly higher (P<0.05) in the control treatment (322.92 g) than in the shaded treatment (287.31 g). The results of this study demonstrate that light intensity has a huge influence on shrimp performance mainly due to the increase in natural food availability.     

Using knowledge of behaviour and optic physiology to improve fish passage through culverts

Culverts reduce connectivity for aquatic animals by being both a hydraulic and physical barrier. However, altered light intensity may also be a behavioural barrier to fish movement, especially for diurnal species that have adapted to moving when it is light. We propose that knowledge of optical physiology and fish behaviour, two important mechanisms underpinning movement, can inform efforts to improve fish movement through culverts. We firstly review the sensory systems of fish with reference to visual sense and explore how this affects fish movement. We then highlight theoretical knowledge that can help us understand fish behaviour and the potential mismatch between the conditions under which fish have evolved and altered conditions within culverts. We describe potential knowledge gaps and directions for future research to improve our understanding of how culverts may affect fish movement. Finally, we explore the potential costs and ecological benefits of different mitigation options to identify those with the most promise for managing the light environment in culverts to facilitate movement. For researchers and managers exploring this subject, we suggest an approach that: (a) identifies light requirements for movement by different species, (b) tests movement under different light conditions and (c) considers an integrative assessment method for testing fish behaviour around culverts. Understanding how optical physiology, fish behaviour and culvert design influence fish movement can improve connectivity for a range of species.     

光照强度对沉水植物生长和光合作用影响的研究进展

沉水植物作为重要的初级生产者,在水生生态系统中有着非常重要的作用。沉水植物的生长和分布受到诸多环境因子的影响,其中水下光照强度、水温和矿质元素等是重要的因子。本文综述了光照强度对沉水植物生长和光合作用影响的研究进展,总结了沉水植物对弱光在形态和生理上的适应机制,并对目前研究中存在的问题和今后的研究方向进行了展望,以期为进一步开展沉水植物生理生态学研究及受损生物群落的恢复提供科学参考。