Effects of stocking density on the growth and immunity of Atlantic salmon salmo salar reared in recirculating aquaculture system(RAS)

Atlantic salmon reared in recirculating aquaculture system(RAS) may lead to inappropriately high stocking density, because ?sh live in a limited space. Finding the suitable stocking density of Atlantic salmon reared in RAS is very important for RAS industry. In this paper, the in?uence of stocking density on growth and some stress related physiological factors were investigated to evaluate the ef fects of stocking density. The ?sh were reared for 220 days at ?ve densities(A: 24 kg/m^3; B: 21 kg/m^3; C: 15 kg/m^3; D: 9 kg/m^3 and E: 6 kg/m^3). The results show that 30 kg/m^3 might be the maximum density which RAS can af ford in China. The stocking densities under 30 kg/m^3 have no ef fect on mortality of Atlantic salmon reared in RAS. However, the speci?c growth rate(SGR), ?nal weight and weight gain in the high density group were signi?cantly lower than the lower density groups and middle density groups. Moreover, feed conversion rate(FCR) had a negative correlation with density. Plasma hormone T_3 and GH showed signi?cant decrease with the increase of the stocking density of the experiment. Furthermore, thyroid hormone(T 3), GH(growth hormone) activities were decreased with stocking density increase. However, plasma cortisol, GOT(glutamic oxalacetic transaminase) and GPT(glutamic pyruvic transaminase) activities were increase with stocking density increase. And the stocking density has no ef fects on plasma lysozyme of Atlantic salmon reared in RAS. These investigations would also help devise effcient ways to rear adult Atlantic salmon in China and may, in a way, help spread salmon mariculture in China.     

Microbial diversity in Huguangyan Maar Lake of China revealed by high-throughput sequencing

Huguangyan Maar Lake is a typical maar lake in the southeast of China. It is well preserved and not disturbed by anthropogenic activities. In this study, microbial community structures in sediment and water samples from Huguangyan Maar Lake were investigated using a high-throughput sequencing method. We found significant differences between the microbial community compositions of the water and the sediment. The sediment samples contained more diverse Bacteria and Archaea than did the water samples. Actinobacteria, Betaproteobacteria, Cyanobacteria, and Deltaproteobacteria predominated in the water samples while Deltaproteobacteria, Anaerolineae, Nitrospira, and Dehalococcoidia were the major bacterial groups in the sediment. As for Archaea, Woesearchaeota (DHVEG-6), unclassified Archaea, and Deep Sea Euryarchaeotic Group were detected at higher abundances in the water, whereas the Miscellaneous Crenarchaeotic Group, Thermoplasmata, and Methanomicrobia were significantly more abundant in the sediment. Interactions between Bacteria and Archaea were common in both the water column and the sediment. The concentrations of major nutrients (NO^3-, PO4^3-, SiO3^2- and NH4^+) shaped the microbial population structures in the water. At the higher phylogenetic levels including phylum and class, many of the dominant groups were those that were also abundant in other lakes;however, novel microbial populations (unclassified) were often seen at the lower phylogenetic levels. Our study lays a foundation for examining microbial biogeochemical cycling in sequestered lakes or reservoirs.     

Effects of stocking density on the growth and immunity of Atlantic salmon salmo salar reared in recirculating aquaculture system (RAS)

Atlantic salmon reared in recirculating aquaculture system (RAS) may lead to inappropriately high stocking density, because fish live in a limited space. Finding the suitable stocking density of Atlantic salmon reared in RAS is very important for RAS industry. In this paper, the influence of stocking density on growth and some stress related physiological factors were investigated to evaluate the effects of stocking density. The fish were reared for 220 days at five densities (A: 24 kg/m³; B: 21 kg/m³; C: 15 kg/m³; D: 9 kg/ m³ and E: 6 kg/m³ ). The results show that 30 kg/m³ might be the maximum density which RAS can afford in China. The stocking densities under 30 kg/m³ have no effect on mortality of Atlantic salmon reared in RAS. However, the specific growth rate (SGR), final weight and weight gain in the high density group were significantly lower than the lower density groups and middle density groups. Moreover, feed conversion rate (FCR) had a negative correlation with density. Plasma hormone T₃ and GH showed significant decrease with the increase of the stocking density of the experiment. Furthermore, thyroid hormone (T₃), GH (growth hormone) activities were decreased with stocking density increase. However, plasma cortisol, GOT (glutamic oxalacetic transaminase) and GPT (glutamic pyruvic transaminase) activities were increase with stocking density increase. And the stocking density has no effects on plasma lysozyme of Atlantic salmon reared in RAS. These investigations would also help devise efficient ways to rear adult Atlantic salmon in China and may, in a way, help spread salmon mariculture in China.

     

Preliminary study on different nutrient pools supplies for the phytoplankton growth in the Jiaozhou Bay in China in the fall of 2004

The source and significance of two nutrients, nitrogen and phosphorous, were investigated by a modified dilution method performed on seawater samples from the Jiaozhou Bay, in autumn 2004. This modified dilution method accounted for the phytoplankton growth rate, microzooplankton grazing mortality rate, the internal and external nutrient pools, as well as nutrient supplied through remineralization by microzooplankton. The results indicated that the phytoplankton net growth rate increased in turn from inside the bay, to outside the bay, to in the Xiaogang Harbor. The phytoplankton maximum growth rates and microzooplankton grazing mortality rates were 1.14 and 0.92 d-1 outside the bay, 0.42 and 0.32 d-1 inside the bay and 0.98 and 0.62 d-1 in the harbor respectively. Outside the bay, the remineralized nitrogen (Kr=24.49) had heavy influence on the growth of the phytoplankton. Inside the bay, the remineralized phosphorus(Kr=3.49) strongly affected the phytoplankton growth. In the harbor, the remineralized phosphorus (Kr=3.73) was in larger demand by phytoplankton growth. The results demonstrated that the different nutrients pools supplied for phytoplankton growth were greatly in accordance with the phytoplankton community structure, microzooplankton grazing mortality rates and environmental conditions. It is revealed that nutrient remineralization is much more important for the phytoplankton growth in the Jiaozhou Bay than previously believed.     

天然气水合物的上界面——硫酸盐还原-甲烷厌氧氧化界面

定义了海域天然气水合物成矿带的上界面。指出在地球深部存在最原始的、从根本上不依靠光合作用来生存的生命系统。根据对ODP岩心样品中微生物数量的统计,海底以下沉积层中的生物数量可能占据全球原核生物总量的70%,其生物总碳量和地球表面所有植物的碳总量相当。地球内部如此巨大的生物总量应该在地壳中的气体分布等方面起着重要作用。甲烷在地壳层中广泛存在,并主要是微生物成因的。微生物产甲烷的途径主要有两个,一是二氧化碳还原,另一个是醋酸盐发酵。相应地,参与产甲烷的微生物菌群主要是产甲烷菌和食醋酸菌。甲烷在沉积层中的厌氧氧化是一个不争的事实。该过程发生在海底以下一个非常局限的区带,称为硫酸盐还原-甲烷厌氧氧化区带。通常,这个区带很窄,仅为一个面,因此,硫酸盐还原-甲烷厌氧氧化区带又称硫酸盐还原-甲烷厌氧氧化界面。这是一个基本的生物地球化学界面,在功能上它起到屏蔽甲烷向海底和大气逸散的作用,是一个巨大的甲烷汇。甲烷的厌氧氧化同样是一个由微生物介导的过程,参与此过程的微生物主要是食甲烷古菌和硫酸盐还原菌。硫酸盐还原-甲烷厌氧氧化界面在海洋沉积层中一般深可达海底以下上百米,浅可至海底。此界面为天然气水合物的上界面,该界面以上没有甲烷...     

南极长城站海雾特征分析

本文根据对海雾气象要素场、大气层结和天气形势的分析及其持续时间和季节、年际变化的统计分析,结合个例,讨论了南极长城站海雾的特征和形成机制。认为长城站海雾大多为平流冷却雾,高频率的偏北风和南大洋极锋附近显著的经向海温梯度是长城站多海雾的根本原因;夏半年海雾要多于冬半年,海雾的年际分布差异明显;海雾可出现于0-17m/s的各级风力中,3-11m/s偏北风最有利于海雾的维持;气温为-2-4℃、气-海温差为0-2℃时最易出现海雾;海雾的发生一般伴有稳定的大气层结;"东高西低"是长城站海雾的主要天气形势;海雾的持续时间取决于高压在南极半岛维持时间的长短,平均有10个小时。     

复合加载条件下吸力式沉箱基础承载特性数值分析

吸力式沉箱基础的承载特性是海洋工程结构设施建造与设计中的一个关键问题。这种新型的深水海洋基础型式,通常承受竖向上拔荷载与水平荷载的共同作用,其工作性能与设计理论远远不能满足工程实践的需要。本文采用有限元分析方法对吸力式沉箱基础的极限承载特性进行数值计算。以大型通用有限元分析软件ABAQUS为平台,通过二次开发,数值实现了Swipe试验加载方法和固定位移比分析方法,针对不同的沉箱长径比、土的强度折减系数,探讨了沉箱基础在垂直上拔荷载和水平荷载单调联合作用下的极限承载力,通过对不同荷载组合的数值计算构造了复合加载条件下沉箱基础破坏包络面。     

波浪作用下孔隙海床-管线动力相互作用分析

波浪作用下海床中的孔隙水压力与有效应力是影响海底管线稳定性的主要因素。然而,在目前的海床响应分析中一般将管线假定为刚性,并不能合理地考虑海床与管线之间的相互作用效应,同时也没有考虑土体和管线加速度对海床动力响应的惯性影响,从而无法确定由此所引起的管线内应力。为此考虑管线的柔性,分别采用饱和孔隙介质的Biot动力固结理论和弹性动力学理论列出了海床与管线的控制方程,进而采用摩擦接触理论考虑海床与管线之间的相互作用效应,基于有限元方法建立了海床-管线相互作用的计算模型及其数值算法。通过变动参数对比计算讨论了管线几何尺寸、海床土性参数对波浪所引起的管线周围海床孔隙水压力和管线内应力的影响。     

闽中近岸西北行路径台风浪波向特征

台风浪的研究对于船舶航行、避风以及港口、海洋和近岸建筑物的安全有着重要的现实意义。本文基于考虑波浪折射、底部损耗及波浪破碎等的波谱模型,在充分考虑风能量输入、白帽耗散、波浪破碎以及波-波间的非线性相互作用等物理过程后,对在福建省中部登陆的0513号"泰利"、0709号"圣帕"和0808号"凤凰"台风引起的台风浪过程进行了数值模拟计算。计算结果与实测数据相吻合,并总结出闽中近岸西北行路径台风浪的波向变化规律。为近岸海域船舶航行和港口工程防灾减灾提供了较为重要的参考依据。