汉丰湖支流浮游植物群落结构及环境因子影响分析

为了准确反映汉丰湖的水环境状况,通过浮游植物监测与环境因子监测相结合,探讨小江中上游汉丰湖入湖支流东河、桃溪河、南河、头道河浮游植物群落结构特征及其与水体理化因子的关系,对水体理化指标和浮游植物进行了采样分析,在东河、南河、桃溪河、头道河各设置3个监测点,于2013年3、6、9、12月各采样1次。结果表明,4条入湖支流共采集鉴定浮游植物8门、84属、218种(含变种),以硅藻(107种)和绿藻(64种)居多,其次是蓝藻(31种),这3类的种数占浮游植物总数的92.7%,其它5门的种类数较少。各支流浮游植物种类数由低到高依次为东河(83种)、桃溪河(100种)、南河(106种)、头道河(120种),其密度均值在105数量级,南河下游浮游植物密度在夏季出现最大峰值,达到1 160×104个/L,在绝大部分时段均以蓝藻占优势。水体理化指标监测数据显示,汉丰湖4条主要支流的总氮、总磷、p H、溶氧、水温、CODMn和电导率均值分别为1.00~1.61 mg/L、0.03~0.11 mg/L、7.82~8.53、6.65~7.03 mg/L、17.9~20.4℃、2.07~4.57 mg/L、269.25~522.50μS/cm;其中,南河的总氮、CODMn较高,头道河的总磷较高,各支流的水温、溶氧、p H较为接近。浮游植物与环境因子的相关性分析表明,东河的裸藻、桃溪河的绿藻以及头道河的蓝藻密度均与水温显著相关(P0.05),南河的硅藻和绿藻密度与水温极显著相关(P0.01),东河的甲藻密度与总磷浓度极显著相关(P0.01),桃溪河的硅藻和甲藻密度与总磷浓度显著相关(P0.05),绿藻密度与总氮浓度显著负相关(P0.05),硅藻密度与总氮浓度极显著负相关(P0.01);浮游植物分布及密度主要受水温、总氮和总磷的影响。     

汉丰湖富营养化综合评价与水环境容量分析

2012、2013年季节性监测了汉丰湖水体理化指标,采用综合营养状态指数法对其富营养化状态进行了评价,采用沃伦威德尔模型(Vollenweider)和狄龙模型(Dillon)计算了化学需氧量、总氮、总磷的水环境容量。结果表明:汉丰湖水质总体处于地表水Ⅱ类~Ⅳ类标准,TN 0.76~2.24 mg/L、平均1.41 mg/L,NH3-N 0.17~0.95 mg/L、平均0.41 mg/L,TP 0.010~0.106 mg/L、平均0.069 mg/L,CODMn2.34~14.60 mg/L、平均4.22 mg/L。东河区域水质优于小江干流、南河区域,秋季污染程度最轻;汉丰湖水体营养状态介于中营养到轻度富营养型,其中南河区域的营养程度相对较高;从单个评价因子看,总氮的营养状态最高,持续处于轻度、中度至重度富营养状态。汉丰湖化学需氧量、总氮、总磷水环境容量分别为37 335、109.1和1 643.84 t/a,为达到汉丰湖水功能区划Ⅱ类水的管理目标,总氮、总磷削减率分别为38%和56%。     

包头南海湖非冰封期浮游植物的时空动态特征

为了解包头南海湖浮游植物群落非冰封期的时空动态特征,2017年5-10月,在南海湖设置了12个监测站位,监测浮游植物时空变化,并同步监测水环境因子。结果表明,南海湖12个站位共鉴定出浮游植物146种(含变种);其中,绿藻门(Chlorophyta)59种,蓝藻门(Cyanophyta)31种,硅藻门(Bacillariophyta)37种,裸藻门(Euglenophyta)9种,金藻门(Chrysophyta)5种,黄藻门(Xanthophyta)3种,隐藻门(Cryptophyta)2种。浮游植物密度为23.35×10~6～115.59×10~6个/L;优势度分析表明,5-6月主要以绿藻占优势,优势种为四尾栅藻(Scenedesmus quadricauda)和螺旋弓形藻(Schroederia spiralis);7-9月主要以蓝藻占优势,优势种为微小平裂藻(Merismopedia tenuissima)和水花束丝藻(Aphanizomenon flosaquae);10月以绿藻和硅藻占优势,优势种为四尾栅藻和近缘针杆藻(Synedra affinis)。空间上呈现出沿进水口向湖心区逐渐递增的趋势,湖心区整体密度较高,而排污口和芦苇区处密度相对较低;冗余分析(RDA)表明,氨氮、化学需氧量、pH、叶绿素-a以及水温是影响浮游植物分布的主要水环境因子,绿藻与总氮关系密切,蓝藻主要受总磷的影响,硅藻受pH影响较大。     

牧野湖浮游植物时空分布及水质分析

2012年9月至2013年8月,按月对牧野湖的水质及浮游植物群落结构开展了初步调查。共发现浮游植物87属147种;其中,黄藻门和隐藻门各6种,金藻门和甲藻门各4种,绿藻门57种,裸藻门23种,硅藻门29种,蓝藻门18种。2012年秋季到2013年春季浮游植物密度在7 400×104~9 100×104个/L,2013年夏季最高,为16 000×104个/L。秋、冬、春季密度较高的为绿藻和硅藻,所占比例:秋季绿藻32.2%、硅藻23.9%,冬季绿藻39.2%、硅藻24.5%,春季绿藻40%、硅藻51.7%;夏季密度较高的种群是蓝藻,占83%。湖区秋、冬、春、夏季Shannon多样性指数分别为1.3、1.27、1.06、0.48,Pielou均匀度指数也从0.35下降到0.175,表明从2012年秋季到2013年夏季牧野湖的水质是不断下降的。皮尔逊相关分析表明,湖区浮游植物的平均密度与Chl-a、CODCr、水温显著正相关(P0.05);与TN、TP、NH+4-N也有一定的正相关性,但未达到显著水平;与SD、NO-3-N之间有一定的负相关,但未达到显著水平。     

乌杨调节坝运行初期汉丰湖浮游植物群落结构及其与环境因子的相关性分析

为了解乌杨调节坝正式运行初期汉丰湖水体情况,2016年10月—2017年10月对汉丰湖浮游植物群落及水质状况进行了调查。结果显示,调查期间共检出浮游植物7门58属114种,其中绿藻门和硅藻门最多,分别占39.47%和38.60%。尖针杆藻、梅尼小环藻和啮蚀隐藻等为优势种。浮游植物平均密度为8.64×10~5 ind./L;平均生物量为2.03 mg/L;其中,平均密度和生物量在2016年12月最小,2017年2—8月不断增大,10月份有所下降;四个采样点的平均密度和生物量差异均不显著。各采样点浮游植物Margalef物种丰富度指数(d_(Ma))为1.69～5.23;Shannon-Wiener指数(H’e)为1.12～2.75;Pielou均匀性指数(J_e)为0.45～0.96。水温、高锰酸盐指数、总磷、总氮、氨氮的变化范围分别为12.7～31.5℃、1.54～4.92 mg/L、0.01～0.18 mg/L、0.20～1.11mg/L、0.10～0.81 mg/L。冗余分析(RDA)结果表明,汉丰湖浮游植物与高锰酸盐指数、总磷、亚硝态氮和氨氮呈正相关,与透明度呈负相关。     

大纵湖浮游植物群落特征及其与环境因子的关系

里下河腹地位于江淮两大水系交融地带,人类活动严重影响区域水生态环境。鉴于浮游植物群落结构及多样性可作为水环境变化重要指示生物,于2015-2017年对里下河腹地典型湖泊大纵湖浮游植物群落结构及环境因子进行逐月采样调查,分别采用藻类生物学指标和综合营养指数对大纵湖营养状态进行综合评价,并且基于相关性分析法,探讨浮游植物与水环境因子的响应关系。结果显示,大纵湖在调查期间共鉴定出浮游植物7门、123种,以绿藻、硅藻、蓝藻为主,分别为50、35、18种,占总种数的40.65%、28.46%、14.63%。全湖各采样点浮游植物的平均丰度为3.70×106 ~6.25×106 个/L;空间上略有差异,夏季藻类丰度较高,冬季最低。大纵湖各个采样点浮游植物优势种基本相同,共8种。浮游植物物种多样性指数和均匀度年均值分别为2.74和0.78,表明大纵湖处于轻-中度污染状态。综合营养指数显示,大纵湖处于轻度富营养状态,两者结果基本一致。相关性分析表明,水温（T）、透明度（SD）、浊度（TUB）和总氮（TN）是影响大纵湖浮游植物群落结构的主要水质指标。     

江苏横山水库浮游植物群落结构的动态变化

研究横山水库浮游植物群落的动态变化特征和综合分析水质,为库区的水资源保护和开发利用提供参考依据。2014年7月至2015年6月,设置5个采样点,每月上旬上午9时左右、天气状况良好时采水样1次。共采集鉴定浮游植物7门63属147种(包含变种及变型),绿藻门28属63种、硅藻门16属46种、蓝藻门10属23种、甲藻门3属6种、裸藻门3属3种、隐藻门2属3种、金藻门1属3种,浮游植物的种类组成为绿藻-硅藻-蓝藻型。浮游植物密度2.3×106~8.0×106个/L、平均4.2×106个/L,硅藻门、绿藻门和蓝藻门密度占比分别为57.3%、29.8%和8.4%。浮游植物的多样性指数H'变化范围为1.52~3.67,平均2.48;均匀度指数J 0.53~0.86、平均0.71;丰富度指数d 0.83~3.32、平均2.05。浮游植物主要优势种为绿藻门的美丽鼓藻(Cosmariumformosulum),硅藻门的变异直链藻(Melosiravarians)、颗粒直链藻(Melosira granulate)、尖针杆藻(Synedraacus)和肘状针杆藻(Synedra ulna)等。相关性分析表明,游植物密度与总磷、水温、透明度呈正相关关系,与溶解氧呈负相关关系,与总氮没有相关关系。硝酸盐和溶解氧对浮游植物密度有显著影响,亚硝酸盐氮、氨氮、CODMn、浊度、p H、UV254的水平变化和浮游植物密度没有相关性。根据浮游植物多样性分析以及富营养化指数值TLI(∑)评价,横山水库水质属于轻度富营养状态。     

红水河流域梯级水库夏季浮游植物群落结构特征

为了解红水河流域水生态系统的健康状态,2009年夏季(6-7月)对其干流龙滩、岩滩、大化、百龙滩、乐滩、桥巩6座梯级水库及主要支流水体中浮游植物的种类组成和分布进行了调查。共鉴定出浮游植物6门、75属、84种,以硅藻种类最多,其次是绿藻和蓝藻;其中硅藻51种,占60.71%;绿藻17种,占20.24%;蓝藻门10种,占11.90%;甲藻门、金藻门、红藻门各2种,分别占2.38%。优势度分析表明,龙滩水库和百龙滩水库浮游植物优势种为硅藻和绿藻,岩滩水库、大化水库、乐滩水库浮游植物优势种为硅藻、绿藻和蓝藻,桥巩水库浮游植物优势种为硅藻、绿藻和金藻;6座水库浮游植物密度变化范围2.12×105~6.03×105个/L,百龙滩水库的密度最高,龙滩水库的密度最低;浮游植物生物量变化范围0.60~2.45 mg/L,龙滩水库的浮游植物生物量最高,大化水库的生物量最低。Shannon-Wiener多样性指数为2.14~3.22,均匀度指数为0.56~0.85。各梯级水库浮游植物组成相似性系数为0.35~0.70,龙滩水库和桥巩水库之间浮游植物组成相似性最大(0.70),岩滩水库和百龙滩水库的相似性最小(0.35)。综合多种指标对水质进行评估,龙滩水库为贫-中营养型,岩滩、大化、百龙滩、乐滩、桥巩水库为贫营养型。     

武汉市夏季养殖湖泊浮游生物测定及比较研究

2007年夏季对武汉市梁子湖、斧头湖、柴泊湖、南湖和野芷湖5个湖泊共13个点的浮游生物进行了监测种类鉴定。5个湖泊有浮游植物133种,其中蓝藻门43种,金藻门1种,黄藻门1种,硅藻门28种,甲藻门6种,裸藻门12种,隐藻门2种,绿藻门40种。浮游动物有43种,其中原生动物14种,轮虫23种,枝角类3种,桡足类5种。5个湖泊浮游植物种类数量排序为:梁子湖>南湖>柴泊湖>斧头湖>野芷湖;浮游动物种类数量排序为:柴泊湖>斧头湖>梁子湖=南湖>野芷湖;浮游植物平均密度排序为:南湖>野芷湖>梁子湖>柴泊湖>斧头湖;浮游植物平均生物量排序为:梁子湖>南湖>斧头湖>柴泊湖>野芷湖;浮游动物平均密度和平均生物量排序均为:柴泊湖>南湖>野芷湖>梁子湖>斧头湖。梁子湖、斧头湖、柴泊湖、南湖和野芷湖的藻型特征分别是蓝藻+硅藻、蓝藻+硅藻+绿藻、蓝藻+绿藻、蓝藻+硅藻+绿藻和蓝藻+绿藻。     

大渡河河口浮游植物群落时空分布特征及其与环境因子的关系

为了探究安谷水电站建成后浮游植物群落时空分布特征及其与水环境因子的关系，于2015年5月至2016年9月对其所在的大渡河河口开展了调查。结果表明，调查区域共采集到浮游植物7门、49属、138种，主要由硅藻（种类数占71.02%）、绿藻（15.95%）、蓝藻（9.42%）、裸藻（1.45%）组成。大渡河河口主河道浮游植物种类数较高，特别是安谷水电站坝下断面最高。浮游植物密度为31.20×104~66.69×104个/L，其组成以硅藻为主，秋季浮游植物密度高于春季。大渡河主河道各样点浮游植物密度水平分布变化大，安谷水电站库区和坝下样点密度显著高于调查河段的其他样点。对比安谷水库蓄水前后，浮游植物种类的季节分布无明显差异，而密度的季节分布则差异明显；浮游植物群落的空间分布发生了显著变化，特别是安谷水电站库区和坝下浮游植物种类和密度明显增加。Person相关性分析显示，影响浮游植物密度的主要因子是水温、流速、透明度，与氮、磷元素的浓度则未显出相关性；RDA分析表明，水温、溶解氧、流速、透明度、总氮是影响浮游植物组成的主要因素。安谷水电站的建设使得水体理化指标及水文情势分布因素发生改变，对浮游植物群落的时空分布造成了直接影响，特别是电站库区和坝下，浮游植物的种类和密度变化明显。     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

This study brings an integrated analysis about the relationship between water deterioration and its physiological consequences in live fish transport. The analysis was focused on the transport water and its deterioration, and physiological challenges imposed on the fish. Usual commercial handling procedures employed to mitigate fish stress during transport were discussed. Future topics of research for the establishment of safer fish transport protocols were proposed. Transport was classified into short (≤8 h) or long transport (>8 h). The main issue in short transports should be the prevention of water pH reduction, while in long transports it is the increase in ammonia. Plasma cortisol is the most employed marker for stress and is acutely elevated upon short episodes of transport, but remains elevated even in long‐transport events. Plasma glucose is perhaps a better marker for handling stress. Plasma lactate, pH, osmolality CO₂ and ions should be more often evaluated. Plasma Na⁺ and Cl^‐ are very useful markers of acidosis, due to their respective exchange for H⁺ and , for acid–base regulation. The establishment of species‐specific transport protocols should be preceded by such combined analyses of water and physiological parameters.     

Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

Effects of cadmium on the kinetics of calcium uptake in developing tilapia larvae, Oreochromis mossambicus

The toxic effects of Cd²⁺ on Ca²⁺ influx kinetics in developing tilapia (Oreochromis mossambicus) larvae were evaluated. Addition of 20 µg l^-1 of Cd²⁺ to the environment of 0 and 3 day-old larvae competitively inhibited the Ca²⁺ uptake within 4h resulting in a great increase in K_m values for Ca²⁺ influx (19.3 and 17.4 fold, respectively) as compared with their respective controls. Consequently, the actual Ca²⁺ influx of larvae in solutions of 0.2 mM Ca²⁺ are suppressed by 32–45%. Also, 3 day-old larvae were more sensitive to internally accumulated Cd²⁺ than 0 day-old larvae. Although the Ca²⁺ influx in 0 and 3 day-old larvae may be restored to the levels of their respective controls with 24h of being transferred to a 20 µg l^-1 Cd²⁺ solution, total body Ca²⁺ content was significantly reduced in 3 day-old larvae. Increased Ca²⁺ uptake efficiency ensures sufficient Ca²⁺ for normal growth. However, rapid increase in Ca²⁺ influx after hatching also leads to higher Cd²⁺ uptake. Exposure to Cd²⁺ will lead to a drop in body Ca²⁺ content resulting in retardation of larval growth. Therefore, we conclude that if Ca²⁺ uptake is interfered with at this critical stage of development, larvae will not be able to maintain normal levels of body Ca²⁺ and will show signs of Cd²⁺ poisoning.     

Migratory dynamics of stream-spawning longnose gar (Lepisosteus osseus)

Abstract– Literature evidence suggests that lake-dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in-stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In-stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in-stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management decisions.     

Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

The desaturation and elongation of [1-¹⁴C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.