宁夏沙湖浮游植物群落结构及多样性研究

于2008年4月-2009年1月对宁夏沙湖浮游植物的种类组成、密度、生物量、优势种以及物种多样性进行了分析研究,并依据浮游植物种类组成和密度,对浮游植物群落结构进行了聚类分析(Cluster Analysis,CA)和多维分析(Multidimensional scaling,MDS)。结果表明,沙湖浮游植物共有8门94属117种,种类构成比例为绿藻49.6%、硅藻21.6%、蓝藻16.0%和其它12.8%。春季优势种的种类较多,蓝、硅、绿藻均有,夏、秋季蓝藻占绝对优势,冬季以绿藻为主。浮游植物种类、密度、生物量和分布依季节而异,高峰期出现在7月,低谷期出现于1月。Margalef指数2.872~4.652,Shannon指数2.058~3.057,均匀度指数0.521~0.759,综合评价沙湖水体为中富营养水平。浮游植物群落结构春、夏、冬季聚为3类,秋季聚为2类,除春季外,MDS分析结果和聚类分析结果一致,支持和证实了聚类分析的结果,很好地揭示了沙湖各季节、各样点间浮游植物群落结构的相似性与差异性。b     

三角湖浮游植物群落结构与水质评价

2011-2012年对三角湖浮游植物进行季节性调查,以了解浮游植物群落结构特征及其对水质的指示作用,为污染防治和生态修复提供依据。结果表明,在三角湖共采集浮游植物94种(变种),隶属于8门、25科、51属;其中,绿藻种类最多,约占总种数的59.6%,其次是硅藻、蓝藻和裸藻,分别占12.8%、11.7%和8.5%,其他门类种类较少。浮游植物细胞密度平均值为(102.32±59.89)×106个/L;其中,蓝藻密度最大,占浮游植物总丰度的86.69%,其次是绿藻和硅藻,分别占7.77%和4.91%,其他门类密度较低。浮游植物密度具有明显的季节变化规律,夏季的密度最大,秋季次之,冬季和春季较低。夏季和秋季蓝藻细胞密度占绝对优势,绿藻和硅藻次之,而冬季蓝藻密度下降,硅藻和绿藻占优势,春季蓝藻又重新占据优势。三角湖浮游植物Margalef丰富度指数、Shannon-Weaver多样性指数和Pielou均匀度指数平均值分别为2.75、1.78和0.46。Shannon-Weaver多样性指数和Pielou均匀度指数以冬季和春季较高,秋季最低,表明冬季和春季浮游植物群落结构相对复杂,而秋季的群落结构相对简单。综合水质生物学和水体理化指标评价结果,三角湖水体为中-富营养型。     

抚仙湖浮游植物群落结构特征及多样性研究

为了了解抚仙湖浮游植物群落结构特征,于2014年9月(秋季)、2014年12月(冬季)、2015年3月(春季)以及2015年7月(夏季)对抚仙湖进行采样,在全湖共设置12个样点,通过野外调查及实验室研究的方法,对抚仙湖浮游植物群落结构及物种多样性进行了分析。结果表明,抚仙湖共有浮游植物8门、66属、101种,种类构成比例中,绿藻占54.46%、硅藻占21.78%、蓝藻占9.90%、其他13.86%;不同季节浮游植物的种类组成差异极显著(P0.01),夏季种类最多,有79种,冬季最少,仅有61种。优势度分析显示,抚仙湖共有优势种4门、13种,其中绿藻门最多,有8种,且在全年均形成优势种,蓝藻在夏季、秋季和冬季成为优势种,硅藻和金藻在春季和夏季形成优势种。抚仙湖浮游植物细胞密度为29.9×104~193.2×104个/L,平均为61.51×104个/L;生物量为0.242~0.567 mg/L,平均为0.455 mg/L。浮游植物Margalef丰富度指数为2.31~3.18,Shannon-Weaver多样性指数为3.14~3.65,Pielou均匀度指数为0.89~0.95,综合评价抚仙湖水体为无污染至轻污染。聚类分析表明,抚仙湖浮游植物的种群结构四季变化明显,不同区域浮游植物的种类和密度差异较大。将抚仙湖浮游植物与国内外典型的贫营养湖泊进行相似性比较,Jaccard相似性指数表明,抚仙湖浮游植物群落与其他湖泊均为极不相似,说明其物种及群落结构具有一定的独特性。     

２０１１年春秋季大渡河河口浮游植物群落结构特征研

对大渡河河口春秋季的浮游植物群落结构特征进行了调查,共采集到浮游植物6门、53属、157种；其中,硅藻种类最多,共109种,占总数的69.43％,其次是绿藻和蓝藻.左侧汊河和青衣江浮游植物种类较多.优势度分析显示,大渡河河口浮游植物优势种季节演替明显.浮游植物平均密度和生物量分别为469 040个/L和0.9051mg/L,均以硅藻最高.浮游植物密度春季高于秋季,生物量则春季低于秋季,青衣江浮游植物密度和生物量较干流低.大渡河河口多样性指数春季平均为3.1728,秋季平均为3.3547;均匀度指数春季平均为0.5300,秋季平均为0.5749.秋季浮游植物多样性指数和优势度均高于春季,青衣江两指标均较干流低.     

三角帆蚌养殖池塘浮游植物群落时空动态及其多样性指数

通过对某一套养有青鱼、鲢和草鱼的2.4 hm2三角帆蚌（ Hyriopsis cumingii）养殖池塘2011-2012年的水质和浮游植物调查，分析了浮游植物群落的时空动态，同时运用细胞密度及群落多样性指数等进行了水质综合评价。调查结果显示，浮游植物群落组成中绿藻44.07％，其次是硅藻（16.95％）；浮游植物群落结构、密度及生物多样性指数都具有明显的季节和月份变化特征。绿藻种类数在秋季最多，硅藻种类数在冬季和春季最多，而蓝藻种类数在夏秋季最多，隐藻种类数在秋季最多；浮游植物细胞密度秋季＞春季＞夏季＞冬季。4月份密度最大，达21.12×106 cells/L，其次是11月份，达到13.68×106 cells/L；整个冬季和春季的3月份浮游植物密度偏低；11次采样获得的 Shannon -Wiener 指数（ H′）与 Simpson 指数（ D ）、 Pielou 指数（ J ）的相关性系数分别达0.934、0.858，说明都具有显著相关性。综合浮游植物细胞密度、多样性指数及污染程度指示种类分析结果，说明该养殖水体处于中污状态。本研究对于利用浮游植物监测三角帆蚌养殖池塘水质综合状况及进行生态评价提供了依据。     

淮河流域西淝河浮游植物群落结构特征

为探究淮河流域西淝河浮游植物群落结构特征及其与环境因子的关系,在2016年和2017年冬季(2月)、春季(4月)、夏季(8月)和秋季(11月)对淮河流域西淝河浮游植物群落结构特征进行研究。结果显示,共鉴定出浮游植物236种(含变种和变型),隶属于8门、103属。其中,绿藻门(Chlorophyta)最多,有37属、83种,占浮游植物物种总数的35.17%;其次为硅藻门(Bacillariophyta)28属、78种,占33.05%;蓝藻门(Cyanophyta)20属、40种,占16.95%。浮游植物群落结构组成及变化显示,蓝藻门物种的细胞密度占绝对优势,其次为绿藻门,分别占总细胞密度的57.04%、17.66%。硅藻门物种的相对生物量最大,其次为绿藻门,分别占总生物量的35.69%和28.81%,且浮游植物细胞密度与生物量均在夏季达到最大值。浮游植物细胞密度为(7.24±1.13)×10~7个/L,生物量年均值为(34.08±3.20) mg/L。Shannon-Wiener多样性指数、Margalef丰富度指数和Pielou均匀度指数为3.27～4.66、2.75～6.10和0.73～0.94。Pearson相关性与RDA分析表明,影响浮游植物群落结构的主要因子有溶解氧、水温、水生植被盖度、电导率、营养盐和透明度。研究结果可为揭示淮河流域浮游植物群落结构特征提供基础理论依据。     

新疆乌伦古湖春、秋季浮游植物群落结构的聚类和多维分析

2007年4月和8月对乌伦古湖浮游植物进行了调查。经鉴定,调查区域内浮游植物共计8门172种(含未定种)。其中绿藻门74种(含未定种),硅藻门50种(含未定种),蓝藻门27种(含未定种),其他种类占12.2%。4月浮游植物平均细胞密度和生物量分别为33.49×104ind/L和0.4552mg/L;8月分别为276.28×104ind/L和3.6578mg/L。依据浮游植物物种组成和细胞密度,利用Bray-Curtis相似性测定,对浮游植物群落结构进行聚类(Cluster analysis)和多维(Multidimensional scaling,MDS)分析。结果显示,春、秋季布伦托海浮游植物群落结构聚为两大类,吉力湖聚为三大类;由于各采样点的水深、水温、pH值、透明度等环境因子的差异导致浮游植物群落结构发生变化,采用聚类和多维分析,有效地揭示了乌伦古湖春、秋季各采样点间浮游植物群落结构的相似性;多维分析与聚类分析结果一致,从二维空间角度证实了聚类结论。乌伦古湖属高纬度地区水体,春、秋两季出现以硅藻为优势类群的浮游植物群落类型;结合乌伦古湖浮游植物的优势种、数量和生物量的检测结果,该湖属于贫-中营养型湖泊。本研究旨在群落结构层面探讨春、秋季乌伦古湖浮游植物的变化规律,为今后进一步合理利用该湖丰富的水生生物资源提供科学依据。     

千岛湖浮游植物群落结构时空分布及其与环境因子的关系

研究千岛湖浮游植物群落结构特征及其与主要环境因子的关联性,为了解千岛湖水环境变动规律及水环境的保护与管理提供依据。沿水流方向在水库上中下游依次设置5个采样点,2010年对千岛湖浮游植物群落开展了周年调查。共鉴定出浮游植物8门223种,其物种数、密度和生物量均主要由硅藻、蓝藻和绿藻组成。不同浮游植物门类物种数、密度和生物量组成比例站点间无显著差异;群落总密度和生物量站点间无显著差异,但有显著的季节变化,它们的垂直分布均呈现先增加后下降的趋势,在4~8 m水层具有最大值。Shannon多样性和Pielou均匀度指数在空间和季节间均无显著差异,但Margalef丰富度指数存在显著的季节和空间差异。聚类分析(CA)和多维尺度分析(MDS)表明,藻类物种组成在站点间无显著差异,但具有显著的季节变化,即分化为春季、冬季和夏秋季3种群落类型,春季群落主要特征种为颗粒直链藻及其狭窄变种和尖尾蓝隐藻,冬季为水华鱼腥藻、颗粒直链藻狭窄变种和脆杆藻,夏秋群落为网状空星藻、水华鱼腥藻和梅尼小环藻。相关性分析表明,浮游植物密度和生物量与水温、pH值、CODMn和Chl-a显著正相关,与SD和DO显著负相关;生物量与Si O2-3-Si显著正相关。典范对应分析(CCA)显示,水温、DO和NO-3-N及pH值是影响浮游植物时空分布的主要因子。     

连环湖铁哈拉泡浮游植物群落结构及其与水环境因子的关系

2021年4月(春季)、7月(夏季)、10月(秋季)和2022年1月(冬季)，采用规范方法调查监测和分析受面源污染的浅水铁哈拉泡(46°30’～46°50’N,123°59’～124°15’E)浮游植物群落结构特征及其与水环境因子的关系，并对湖泡水生态保护和治理提出了建议。连环湖铁哈拉泡共鉴定出浮游植物7门66属115种及变种，绿藻门、硅藻门和蓝藻门种类优势占比较大，占总种类数的85.22%。浮游植物的总平均丰度为464.4×10⁴ind./L，总平均生物量为1.533 3 mg/L，绿藻门、硅藻门和蓝藻门丰度和生物量均高于其他门类，其中蓝藻门平均丰度(217.8×10⁴ind./L)和平均生物量(0.489 4 mg/L)均最高。铁哈拉泡浮游植物群落结构季节变化显著，春季蓝藻门、硅藻门和绿藻门为优势门类；夏季和秋季分别为蓝藻门的微囊藻(Microcystis sp.)和硅藻门中的小环藻(Cyclotella sp.)凸显出较大优势；冬季则演变为隐藻门、裸藻门、甲藻门和硅藻门共同占优势的群落结构。TSIM评价结果表明，湖泡营养状态为轻微的富营...     

沅水浮游植物群落结构特征

于2005年3、6、9、12月对沅水浮游植物群落结构进行了调查。结果表明:沅水浮游植物共计6门147种,以硅藻和绿藻为主,分别占43.53%和36.73%。浮游植物平均密度为2.21×105ind./L,蓝藻密度最大为1.33×105ind./L;浮游植物平均生物量为3.97 mg/L,蓝藻生物量最大为3.42 mg/L。浮游植物季节变化比较明显,密度秋季最大(4.64×105ind./L),夏季最小(1.6×104ind./L);生物量冬季最大(12.86 mg/L),夏季最小(0.2 mg/L)。水平分布密度和生物量均是牛鼻滩站最大,分别为6.03×105ind./L和29.6 mg/L。调查显示沅水浮游植物中巴豆叶脆杆藻、颗粒直链硅藻、钝脆杆藻、美丽星杆藻、细星杆藻、格孔单突盘星藻、泥污颤藻、铜绿微囊藻等为优势种。浮游植物Shannon-Wiener多样性指数较低,在1～2之间。指数变化由高到低分别为冬季、秋季、春季、夏季。     

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.     

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.     

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.     

美人鱼发光杆菌对凡纳滨对虾非特异性 免疫功能及抗病力的影响

在基础饲料中分别添加0.1%和1%美人鱼发光杆菌灭活菌、0.1%美人鱼发光杆菌活菌配制成3种免疫实验饲料,以基础饲料为空白对照组饲料,每组设3个平行样。对个体质量为(4.83±0.36)g的凡纳滨对虾进行为期20 d的饲养实验,分别在0、5、10、15和20d进行取样,以血清中的酚氧化酶(PO)、酸性磷酸酶(ACP)、碱性磷酸酶(AKP)、超氧化物歧化酶(SOD)和溶菌酶(UL)活性为免疫指标,探讨了美人鱼发光杆菌作为免疫制剂对凡纳滨对虾非特异性免疫效应的影响;在投喂免疫饲料后的第22天,按0.004 2 kg/kg体重的剂量,直接投喂对虾白斑综合征病毒(WSSV)病料,并记录累积死亡率。结果表明,美人鱼发光杆菌免疫实验组对凡纳滨对虾血清中PO、ACP、AKP、UL和SOD活性影响明显高于对照组,并且在饲料中添加美人鱼发光杆菌后,明显提高了对虾抵御WSSV感染的能力。其中0.1%美人鱼发光杆菌活菌实验组的抗病毒感染能力最强,WSSV感染14d内累计死亡率为63.3%±5.8%;而对照组为96.7%±3.3%。研究表明,美人鱼发光杆菌添加在对虾饲料中能提高凡纳滨对虾非特异性免疫水平,增强抵抗疾病的能力,将其作为对虾免疫增强剂具有良好的应用前景。     

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.