水产养殖水体遥感动态监测及其应用

以安徽省巢湖市为实验区,以国产高分一号(GF-1)和资源三号(ZY-3)高分辨率遥感影像为数据源,以NDWI和纹理特征作为分类特征,联合随机森林、支持向量机和BP神经网络3种分类方法,发展了一种集成分类模型,用于提取养殖水体信息,并进行阴影剔除和形态学处理。结果表明,该集成分类模型适用于提取养殖水体信息,总体精度为97.4%,Kappa系数为0.87,漏分误差为3.7%,错分误差为6.4%,相比单个模型精度明显提高;针对GF-1影像的增强阴影水体指数,对山体阴影和城市建筑阴影的剔除效果明显,较大程度上避免了阴影对水体提取的干扰;实验区养殖水体的遥感动态监测应用发现, 2016年相比2013年水产养殖面积增加6.9%。该研究理论与技术成果的应用,有助于及时掌握养殖水体的时空分布及动态变化,快速提升中国渔业管理的信息化和科学化水平。     

基于景观格局的鄱阳湖生态经济区湿地时空变化

鄱阳湖生态经济区湿地是我国重要的淡水湖湿地,也是国际上重要的生态湿地。但近年来该地区湿地呈现出萎缩退化的趋势,生态功能也逐渐下降。因此,对该地区湿地的动态变化及变化驱动力研究就显得尤为重要。本文基于eCognition面向对象的最邻近域法,选取最优特征组合,对鄱阳湖生态经济区1995,2005,2015三期遥感影像进行解译和分类提取。同时采取动态度和景观格局指数等指标对20年间该地区湿地的动态变化特征进行分析,并采用地理探测器研究其变化驱动力,从而为湿地变化预测及保护提供依据。结果表明：(1)从分类结果看,eCognition面向对象的分类方法对湿地影像的提取效果良好,三期影像分类结果总体精度均大于85%,Kappa系数大于0.85,分类结果较好 (2)鄱阳湖生态经济区1995至2015年间湿地总体面积减少,总体变化率为-22.7%。其中,减少最多的是天然湿地,共减少191083.19hm_²。(3)鄱阳湖生态经济区20年间湿地的总体特征表现为各景观层次上总体变化较小,但各类斑块破碎化程度加大。(4)地理探测器结果表明人口密度、年均温及坡向均对湿地变化的空间分异有较强的解释能力,人口密度对湿地变化空间分异的解释能力高于年均温和坡向。本研究可以为鄱阳湖生态经济区湿地保护提供理论依据及数据支撑,也可以为我国及其他地区淡水湿地保护提供经验借鉴。     

１９８７－２００４年洞庭湖典型湿地类型动态分析

洞庭湖湿地是我国重要的湖泊湿地,先后经历了大范围围湖造田和退田还湖。选取1987年12月、1995年12月和2004年12月3期TM遥感影像,通过决策树分类方法对其进行分类,计算土地利用类型转移矩阵,对洞庭湖典型湿地类型面积动态变化进行分析,以了解1987-2004年退田还湖前后自然湿地与人工湿地相互转化状况,为今后洞庭湖湿地保护提供数据支撑。结果表明,1987-2004年,人工湿地减少,自然湿地增长,增长主要集中在草滩地和芦苇滩地,草滩地增长速率为23.85km2/a,芦苇滩地增长速率为1.97km2/a。1987-1995年,尽管湿地总体上呈现增长,但自然湿地退化严重;1995-2004年,人工湿地呈现下降趋势,在自然湿地中,水域与泥沙滩地总体变化不明显,芦苇滩地与草滩地呈现增长。退田还湖对湿地保护起到了主要作用,但仍存在一些围湖造田现象,退田还湖工程实施没有得到完全落实。     

基于高分卫星影像的秦皇岛近海浮筏养殖分布遥感监测

利用高分一号、高分二号和北京二号等多源国产高分卫星遥感影像,采用面向对象分类方法,结合目视解译,提取了2015-2018年秦皇岛近海浮筏养殖信息,分析了浮筏养殖分布范围与分布面积的年际变化特征。结果表明:秦皇岛近海浮筏养殖主要分布在昌黎县近海海域,每年面积百分比在93%以上;而北戴河区和山海关区则是零星分布,且不是持续分布。近几年秦皇岛近海浮筏养殖总面积呈上下波动的变化趋势,以2016年数值最大,其次为2018年,2015年和2017年相对较小。随着北戴河及相邻地区近岸海域环境综合整治工作的推进,2018年北戴河附近海域已无浮筏养殖分布。     

1980-2018年扎龙湿地及乌裕尔河流域景观格局演变及其响应

研究扎龙湿地及其上游乌裕尔河流域的景观格局演变，为湿地生态系统的管理与保护提供参考。利用研究区内1980-2018年5期土地利用遥感数据，运用GIS空间分析和主成分分析法，分析了区域景观格局时空变化及其驱动力。结果表明：（1）耕地面积从1980年的8629.648629km2增加至2018年的9527.909528km2；水域面积、居工地面积和盐碱地面积分别增加45.7446、57.9358和18.4618km2；林地面积、草地面积和沼泽地面积分别减少231.90232、742.33743和46.1646km2。1980-2000年研究区域其他土地利用类型转移为耕地的面积1035.861306km2，草地转移为其他土地利用类型的面积845.85846km2，其他土地利用类型面积总体变化不大。（2）景观格局指数不稳定，沼泽湿地面积是扎龙湿地的优势景观类型，耕地是乌裕尔河流域的优势景观类型，除优势景观类型外各种景观类型破碎化严重，景观丰富度越来越低。（3）景观格局的变化是自然气候和社会经济发展共同作用的结果，社会经济变化中的人均GDP、第一产业值以及城镇人口数量是导致整个研究区域湿地景观格局变化的主要驱动力；年均径流量与扎龙湿地内部草地的变化正相关。     

围填海对珠江口南沙湿地资源与生物资源的影响

利用1989、1994、2004和2014年陆地卫星遥感资料,采用遥感影像解译手段、GIS数字化和叠加分析等方法,分析珠江口南沙湿地围填海开发进程,并通过对2002—2003年和2013—2014年两个时期10个航次的现场调查资料的对比分析,研究围填海对南沙周围水域生物的影响。结果表明:(1)4个时相南沙湿地海岸线长度分别为213.6 km、230.0 km、232.5 km和248.6 km。1989—1994年、1994—2004年和2004—2014年海岸线长度年增加幅度分别为3.28 km/a、0.25 km/a和1.61 km/a,海岸线向海推进最大距离分别为4900 m、1700 m和7700 m。(2)1989—2014年南沙湿地因围填海增加面积约46.3km~2,增加幅度最大的阶段为1989—1994年,增加面积占总增加面积的40.60%;其次是2004—2014年,增加面积占总增加面积的34.99%;1994—2004年围填海占用的滩涂面积最小(24.41%),南沙万顷沙和龙穴岛的围填海活动最为剧烈。(3)近10年来,南沙湿地浮游动物、大型底栖动物、潮间带生物、鱼类和头足类等生物资源种类分别减少了60.34%、73.21%、26.67%、79.78%和50.00%,栖息密度分别减少58.49%、12.38%、79.96%、78.78%和66.79%,生物量分别减少了82.16%、73.23%、15.83%、70.49%和62.43%。甲壳类的种类数和栖息密度分别减少了13.33%和69.85%,但生物量增加了114.20%。(4)浮游动物多性性指数增加了10.24%,大型底栖动物、潮间带生物、鱼类、甲壳类和头足类等多样性指数分别减少了71.10%、91.82%、18.18%、66.90%和73.68%,优势种更替显著。可见,南沙湿地围填海不仅改变了海岸线的类型和长度,占用了湿地资源,同时也对周边水域的海洋生物产生了不利影响。     

东北地区湿地遥感监测与景观分析

分析东北地区湿地的时空变迁特点,可为东北地区湿地资源的合理利用、合理分配湿地资源、制定东北地区湿地保护和利用相关政策提供科学依据。以1975年MSS遥感图像、2013年CBERS遥感图像为数据源,借助于地理信息系统软件,采用人机交互目视解译的方法,并根据所建立的遥感解译标志,在遥感图像中解译出东北地区湿地信息;引入马尔科夫转移矩阵、重心迁移、景观格局等多种分析方法,探讨东北地区湿地时空动态变化特点。结果表明:近40年来东北地区湿地面积总体呈减少趋势,其中沼泽湿地面积减少24 769.9 km~2、河流湿地面积减少6 753 km~2、人工湿地面积增加22 017.4 km~2;非湿地与湿地各类型间转化明显,其中,沼泽湿地向非湿地、人工湿地转化显著,非湿地向沼泽湿地、人工湿地转化显著;湿地重心总体向南偏西方向迁移36.5 km,其中,人工湿地重心向北偏东方向迁移354.7 km、沼泽湿地重心向南偏西方向迁移261.4 km。景观格局分析显示,东北地区湿地总体向破碎化、多样化与不规则化发展。     

扬州市湿地景观格局演变及驱动力研究

以扬州市2002年、2007年、2013年的遥感影像为数据源,通过解译获得了扬州市湿地资源分布图,运用转移矩阵法及景观格局指数法对2002-2013年间扬州市湿地动态变化及景观格局演变进行分析,并利用主成分分析法对其驱动力进行探究。结果表明,扬州市2002-2013年湿地面积呈逐年下降趋势,2007年比2002年减少13.69 km2,降幅1.1%;2013年比2007年减少43.23 km2,降幅3.3%。2013年与2002年相比,河流面积稍有减少,降幅为5.6%;滩地面积增加73.2%;库塘面积所占比重由49.84%上升到55.37%,面积增加6.2%;湖泊面积降幅29.7%,所占比重由32.83%下降到24.14%。2002、2007、2013年,各湿地斑块所占景观面积比均为库塘>湖泊>河流>滩地。景观格局指数分析表明,湖泊、滩地及库塘呈现不同程度的破碎化,而河流湿地斑块形状趋于规则且连通性较好。扬州市湿地景观整体呈破碎化趋势,湿地斑块形状趋于复杂,景观多样性增加,各类型湿地呈均衡化趋势发展。社会经济发展、人口增加、第二产业比重及降雨量变化是导致湿地景观格局变化的主要驱动力。     

黄河下游湿地演变与实测径流相关性研究

探索不同类型河道湿地面积与水文站实测径流量的相关性，为黄河流域生态保护修复和管理工作提供支撑。选择黄河下游花园口-利津河段为研究对象，基于1986、1990、2000、2010和2020年5期遥感解译黄河下游湿地的类型、面积和格局，分析湿地动态变化及原因，结合黄河下游重要水文站实测径流量数据，探索黄河下游不同类型河道湿地面积变化与径流相关性。结果表明：（1）河流水面湿地为黄河下游河段湿地的主要组成部分，占湿地面积的45.9%~65.9%；（2）黄河下游河段的湿地面积从上世纪80年代至今虽然呈现萎缩趋势，面积减少约35.6%，但萎缩速度在不断减缓，湿地面积逐渐趋于稳定；（3）黄河下游游荡型、弯曲型和顺直型河段的湿地面积与径流量的相关性存在差异。游荡型和弯曲型河段河流水面面积与流量均呈正相关关系，但变化幅度不同，顺直型河段河流水面面积受流量的影响较弱，游荡型、弯曲型河段和顺直型河段滩地面积随径流量增大而减少，减少幅度各有差异，3种河段在不超过某一流量下，河流湿地的面积保持稳定，而超出一定流量范围后，湿地总面积均增加。     

星海湖湿地土地利用变化及其生态需水研究

星海湖是干旱地区典型城市湖泊湿地,其生态环境及生态需水量极大程度上受土地利用变化及相关政策影响。以星海湖湿地为研究对象,利用GIS-遥感技术解译影像,提取不同时期土地利用类型面积,通过水量平衡原理、FAO56Penman－Monteith法开展1996-2018年星海湖湿地湖泊及周边植被生态需水研究,旨在为石嘴山市的生态环境保护、水资源合理利用及优化配置提供科学依据。结果表明：（1）星海湖土地利用格局以水域为主,建设用地、草地次之。水域面积整体呈现增长态势,从6.42km2（占比6.42%）增加至43.11km2（占比43.11%）;区域植被面积仅在1996-2005年期间迅速增加,增加至20.68km2(占比44.35%),之后逐年减少,至18年植被总面积为9.21km2（占比19.64%）。（2）星海湖湿地生态需水总量整体呈增长态势,仅在2014年有所下降,在2018年生态需水总量达到最高：最小生态需水总量为13449.80×104m3,适宜生态需水总量为13674.34×104m3;1996年生态需水总量达到最低：最小生态需水总量为2177.11×104m3,适宜生态需水总量为2314.37×104m3。合理的土地利用配置及管理,对水资源合理规划管理及局部生态环境改善、维护区域生态安全具有重要意义。     

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.     

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.