北部湾鱼类多样性及优势种的时空变化

根据2007年在北部湾进行的4季渔业资源底拖网调查资料,对该海域鱼类的种类组成、物种多样性和优势种的时空变化进行分析.本次调查共捕获鱼类323种,隶属于18目101科,以发光鲷(Acropoma japonicum)、黄斑M(Leiognathus bindus)、竹??鱼(Trachurus japonicus)、二长棘鲷(Parargyrops edita)和大头白姑鱼(Argyrosomusmacrocephalus)为主要优势种.分析结果表明,北部湾鱼类的优势种更替明显,总体趋势为k选择种类(以红笛鲷和黑印真鲨等为代表)被r选择种类(发光鲷、鲾科和天竺鱼科等为代表)所替代,即寿命长、个体大和营养级高的鱼类种类减少,寿命短、个体小和营养级较低的种类增多.鱼类的Shannon-Wiener多样性指数(H)以共同渔区北部海域最高(3.60),东北部海域次之(3.58),共同渔区南部海域最低(2.35),四季多样性指数为2.96～3.77,平均3.31.2007年多样性指数比 1992-1993年低,但高于1998-1999年,表明近年来该海域捕捞压力有所减缓,使得渔业资源有一定的恢复.本研究旨在了解北部湾生物多样性和优势种的动态变化及演替状况,为该海域渔业资源的合理开发与可持续利用对策提供科学依据.     

北部湾东北部游泳生物资源现状

2009年至2010年对北部湾东北部海域游泳生物调查研究表明，该海域共有游泳生物300种，其中鱼类有209种（硬骨鱼类205种，软骨鱼类4种），隶属15目、70科、119属；甲壳类76种；头足类15种。底层鱼类100种，近底层鱼类72种，中上层鱼类29种，岩礁性鱼类8种，分别占鱼类总数的47．85％，34．45％，13．87％和3．83％。暖水性鱼类153种，暖温性鱼类55种，冷温性鱼类1种，分别占鱼类总数的73．20％，26．32％和0．48％。游泳生物种类数季节变化为夏季〉秋季〉春季〉冬季；资源密度指数季节变化为夏季〉秋季〉春季〉冬季；渔业资源密度随季节变化为夏季〉秋季〉春季〉冬季，渔业资源年平均资源密度为522．925kg·km^-2，约相当于该海域原始渔业资源密度的1／10；生物多样性指数以夏、秋季最高。估算了北部湾东北部海域潜在渔业资源量为1．092×10^5t·a^-1，最大可捕量为5．460×10^4t·a^-1。比较了北部湾渔业资源的历史变动情况，对渔业资源的进一步养护和管理提出了建议。     

黄海典型断面渔业资源结构的季节变化

为了解黄海渔业资源结构的动态变化,实验基于2006年9月(秋季)和12月(冬季)、2007年3月和5月(春季)对黄海南部三个典型断面(S1断面位于南黄海南部北部水域,S2断面位于黄海和东海交界处,S3断面位于黄海南部中部水域)的渔业底拖网调查数据,对黄海断面的渔业种类更替、生物量变动、多样性季节变化及其与环境因子的关系进行了初步分析.结果显示,各季节调查共捕获渔业生物156种,其中鱼类109种,底层鱼类占89.0％.各季节前10位渔业种类的渔获量均占总渔获量的60％以上,且主要渔业种类组成变化不大,以小黄鱼、黄(鮟)(鱇)、细纹狮子鱼、鳀和脊腹褐虾等为主.各季节S2断面的主要渔业种类组成有显著变化,而S1和S3断面的主要渔业种类组成变化不大,但各种类渔获量在总渔获量中的比例变化很大；各断面渔业生物个体体质量一般都小于40 g.黄海南部海域从南向北各断面渔业种类多样性递减；各季节的渔业种类数与群落丰富度指数呈正相关.研究表明,黄海各断面渔业资源结构从北向南存在明显的季节变化,并且与底层温度和盐度的关系密切.     

宁夏沙湖沉水植物恢复初期沉积物细菌群落特征研究

探究北部湾春季鱼类多样性变化及与环境因子的关系，为北部湾海域渔业资源的变化及渔业资源的长期开发、利用和保护提供参考。根据2011年和2018年春季北部湾渔业资源调查数据，结合海表面温度（SST）、叶绿素a浓度（Chl-a）遥感数据及水深数据，采用典范对应分析（CCA）和冗余分析（RDA）方法，研究北部湾鱼类优势种和常见种丰度、鱼类多样性指数与环境因子之间的关系。结果表明：2018年春季鱼类捕获种类数高于2011年春季，分别为157和135种；2011年春季优势种为竹荚鱼（Trachurus japonicus）、蓝圆鲹（Decapterus maruadsi）及鹿斑鲾（Secutor ruconius），而2018年春季优势种为竹荚鱼、二长棘犁齿鲷（Evynnis cardinalis）及日本发光鲷（Acropoma japonicum），竹荚鱼为共有优势种。2011年与2018年春季鱼类多样性指数无显著差异（P > 0.05）。CCA和RDA分析结果表明：SST与北部湾鱼类优势种和常见种丰度呈显著正相关性(P < 0.05)，而与鱼类多样性指数呈负相关；水深与北部湾鱼类优势种和常见种丰度呈正相关性，而与鱼类多样性指数呈负相关；同时，Chl-a浓度与北部湾鱼类优势种和常见种丰度呈显著负相关(P < 0.05)，而与鱼类多样性指数呈显著正相关性(P < 0.05)。     

秋季黄海底层鱼类群落结构的变化

根据1985年和2000年秋季渔业生物资源底拖网调查资料，分析了黄海底层鱼类群落结构的时空变化。结果表明，渔业资源优势种的组成随区域和时间不同有着较大的差异。黄海北部和中部渔获种类组成相似性较高，北部与南部、中部与南部的相似性较低；黄海渔获生物种类组成年间相似性较高，为65。进一步的单因子ANOSIM分析表明黄海底层鱼类群落不同区域和年间种类组成没有显著性差异。黄海渔业生物多样性由北向南递减。与1985年相比，2000年鱼类群落长度谱表现出小型种类和小个体增多，大个体减少，且长度范围变小；主要优势种的长度组成也呈现小型化趋势。长度谱区域变化则是从北部向南部小个体数量增多，大个体数量减少。     

莱州湾渔业资源群落结构和多样性的年际变化

根据2009-2013年每年8月在莱州湾水域进行的渔业底拖网调查数据,采用生态多样性指数和多元统计分析等方法,研究了该海域的渔业资源群落结构和多样性特征的年际变化.结果显示,调查共鉴定出100种资源种类,其中鱼类56种;渔业资源种类和资源量存在明显的年际变化,2013年渔业资源种类数为2012年种类数的84.4％,仅为2009年的60.3％,平均网获质量明显下降.鱼类优势种组成存在年际更替现象,主要由经济价值高、个体大的种类向经济价值低、个体小的种类演替.各生态多样性指数均呈现下降趋势,Margalef种类丰富度指数(R)变化范围为2.67-3.95,Shannon-Wiener多样性指数(H')变化范围为0.70-3.83,Pielou均匀度指数(J')变化范围为0.12-0.63.聚类分析(CLUSTER)和多维标度分析(MDS)分析表明,在相同的相似性水平上分组,组内平均相似性与组间相异性变大.单因子相似性分析(ANOSIM)表明,各年渔业群落结构均存在显著差异(P＜0.05).综上所述,莱州湾渔业资源逐年衰退,优势种更替明显,群落结构发生明显变化,多样性呈下降趋势.     

黄河入海泥沙年际通量对莱州湾渔业资源结构的影响

根据2009年8月-2013年8月莱州湾海域渔业拖网调查数据,分析该海域渔业种群组成、优势种、空间分布和资源量的年际变动,以了解黄河入海泥沙通量对莱州湾渔业结构的影响.结果表明:(1)莱州湾渔业资源量整体呈下降趋势,主要以鱼类为主,甲壳类次之,头足类最少;鱼类中以中上层鱼类为主,网获量明显多于底层鱼类,但2011年8月底层鱼类稍多于中上层鱼类;(2)莱州湾渔业资源各年份的优势种有所变动,中上层鱼类和底层鱼类的优势种变动较大,甲壳类优势种变动较少,鱼类优势种组成存在年际更替现象,主要由经济价值高、个体大的种类向经济价值低、个体小的种类演替.主要优势种集中于斑鲦、矛尾鰕虎鱼、口虾蛄、小带鱼和日本枪乌贼等种类.2010年斑鲦大量暴发,为唯一优势种;(3)2009-2013年黄河入海泥沙年际通量与鱼类种数、底层鱼类数和渔业资源数存在显著相关性,与底层鱼类生物量存在极显著相关性.综上所述,黄河入海泥沙年际通量的变动对莱州湾渔业资源量和资源结构都产生了一定影响.     

以数量生物量比较曲线评价东海鱼类群落的状况

利用1997-2000年东海渔业资源的调查资料，应用数量生物量比较曲线（abundance-biomass comparison curves，简称ABC曲线）方法及生物量谱分析东海鱼类群落的状况。调查过程中共出现的鱼类有350种，隶属于29目、121科、239属。按数量排序，前57种鱼类的累积数量百分比达到了99％，其中48种类的平均个体体质量低于50g，占84．2％，这些鱼的累积数量百分比高达97．7％，生物量百分比为82．5％；平均个体体质量在50-100g之间的种类有6种，而平均个体体质量大于100g的种类只有3种。主要优势种类为竹笑鱼（Trachurus japonicus）、发光鲷（Acropoma japonicum）、鲲（Engraulis japonicas）、七星底灯鱼（Benthosema pterotum）、鳄齿鱼（Champsodon capensis）、带鱼（Trichiurus japonicus）等。春季、夏季和冬季东海鱼类群落的ABC曲线显示群落的数量优势度曲线高于生物量的优势度曲线；秋季其数量优势度曲线与生物量优势度曲线相交，4个季节根据ABC曲线计算的形统计值的变化范围为-0．035～-0．077，冬季形统计值最低，其次为秋季，夏季最高。根据Warwick（1986）的划分标准，东海的鱼类群落处于严重干扰状态。从东海鱼类群落生物量谱来看，4个季节标准化生物量谱线性回归的斜率均小于-1，东海鱼类群落的生物量随着个体体质量的增加而逐渐减少，群落的生物量主要集中于较小个体体质量区间内。虽然东海鱼类群落状况在某些季节呈现好转，但其种类组成中小个体的比例仍然较高，主要种类组成中绝大多数种类（如鲲、发光鲷、七星底灯鱼等）的成体个体较小，各季节的数量和生物量百分比都相对较高；也包括一些个体大小差异较大的种类（如带鱼、小黄鱼、竹笑鱼等）。由于幼鱼补充、生长等原因导致它们数量、生物量以及平均个体体质量的季节变化较明显。而一些平均个体体质量较大的种类如蓝点马鲛（Scomberomorus niphonius）、刺鲳（Psenopsis anomala）、黄鳍马面纯（Thamnaconus septentrionalis）仅在某些季节为优势种类，但其生物量百分比远低于某些小型种类的生物量百分比。     

海南岛上岸渔获调查与分析

上岸渔获调查是调查渔业资源的主要方法之一。通过2010年9月至2011年8月监测海南岛主要渔港渔情，统计分析渔获上岸量、渔获组成和作业类型，评估南海渔业资源开发现状并提出建议。结果表明，1）低值幼鱼渔获比例超过40％，经济渔获蓝圆鲹（Decapterusmaruadsi）、带鱼（Trichiurushaumela）、马鲛（Scomber-morus）、眼镜鱼（Menemaculata）、金线鱼（Nemipterus）和头足类（Cephalopoda）的总和不足25％；2）蓝圆骖和带鱼是海南岛上岸渔获的优势种；3）拖网是海南岛近海渔获量最高的作业类型；4）海南岛近海底层渔业资源已严重衰退，远海中上层渔业资源具有巨大开发潜力。建议禁止海南岛近海拖网生产，允许南海休渔期间灯光围网和灯光罩网生产，通过增加远海作业船只的柴油补贴等途径扶持灯光围网和灯光罩网生产，构建“养护近海渔业、开发远海渔业”的新捕捞格局。     

珠江口浅水域小型虾拖网渔获组成分析

拖虾是广东省沿海捕捞渔业的主要作业方式之一。为了查明小型虾拖网的渔获组成及其对渔业资源的影响，2006年10～11月对在珠江口浅水域进行捕虾作业的虾罟网渔船进行了海上渔获组成抽样调查。研究结果表明，珠江口浅水域虾罟网的渔获种类多、组成复杂，幼鱼和副渔获的比例高；主要渔获种类是周氏新对虾Metapenaeus joyneri（18．57％）、矛形梭子蟹Portunus hastatoides（15．48％）、脊尾白虾Exopalaemoncarinicauda（11．50％）和斑节对虾Penaeusmonodon（11．16％），刀额新对虾Metapenaeus ensis、脊尾白虾、白姑鱼Argyrosomus argentatus、海鳗Muraenesocidae和银鲳Pampusargenteus渔获100％为幼鱼，凤鲚Coiliamystus和棘头梅童鱼CoUichthys lucidus幼鱼比例分别高达87．65％和96．15％；周氏新对虾、脊尾白虾、斑节对虾为主捕对象，鱼类和蟹类是主要的副渔获种类；虾罟网捕捞对渔业资源造成一定程度的破坏。     

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.