雅砻江中下游鱼类栖息地评价与保护方案

采用Barbour（1996）提出的栖息地评价指标体系,由底质、栖息地复杂性、流速和水深结合特性、堤岸稳定性、河道变化、河水水量状况、植被多样性、水质状况、人类活动强度和河岸土地利用类型共计10项指标构成雅砻江中下游鱼类栖息地评价指标体系,并依之对雅砻江中下游干流及其主要支流共985 km江段的鱼类栖息地进行了评价。评价结果是无“较差”河流;卧龙寺沟为“一般”; 达曲河为“较好”;其他河流“好”。基于此结果,建议雅砻江中下游按照“两区一段”和局部水域进行栖息地保护,将两河口库尾3.9 km保留河段、34.8 km变动回水区域、支流曲入河作为中游高原鱼类栖息地保护水域,将桐子林坝下及邻近水域作为雅砻江汇口栖息地保护水域,将锦屏二级闸厂址119.0 km大河湾段作为下游东部江河平原鱼类大河湾保护水域。局部水域主要指鳡鱼河支库及其源头支流永兴河、惠民河、达曲河、力丘河、色物绒沟。针对不同河段的保护功能与鱼类栖息地现状,提出了开展相关研究、监测和生态修复等对策的建议。     

赤水河河源段栖息地现状评价及修复对策探讨

对受损栖息地进行保护与修复是复苏河湖生态环境的重要举措。本文以赤水河河源段为研究区域，综合考虑区域内小水电拆除对鱼类栖息地的影响，依据AHP-熵权法，筛选了金沙鲈鲤、青石爬鮡、圆口铜鱼、岩原鲤、昆明裂腹鱼、长薄鳅六种优先保护鱼类，构建了基于河流地貌特征、水文、水质及鱼类等四方面的河道栖息地健康评价指标体系，建立了多尺度赤水河河源段栖息地综合评价标准。评价结果显示该河段仅30%河道栖息地为较好状况，50%河道栖息地处于一般状况，20%河道栖息地处于较差状况。小水电拆除可以有效恢复鱼类栖息地，但其质量仍需进一步提升，结合对研究区栖息地现状评估结果，可采取河道清理、卵砾石注入、河段平面形态修复等五种修复对策。     

大渡河金川至丹巴河段干、支流鱼类资源及其多样性分布

为进一步了解大渡河金川至丹巴河段干、支流鱼类群落结构及其多样性分布特征，2020年5和9月、2021年5和7月对大渡河上游金川电站坝址至猴子岩电站库尾108km干流及区间主要支流进行了系统的鱼类资源调查与分析。结果显示：研究河段共分布有鱼类19种，隶属3目6科11属；鲤形目种类最多（15种），占总种数的78.95%；鲇形目（3种），占15.79%，鲑形目（1种），占5.26%。土著鱼类（14种）主要为裂腹鱼亚科、高原鳅属和爬鮡属等适应高山峡谷流水生境、特化程度较高的鱼类。其中，大渡河裸裂尻鱼（Schizopygopsis chengi chengi）、细尾高原鳅（Triplophysa stenura）和齐口裂腹鱼（Schizothorax prenanti）为研究河段的优势种。渔获物统计及多样性分析表明，干流与小金川、革什扎河、东谷河及勒乌沟等支流土著鱼类组成较为相似，但干流与支流以及各支流间鱼类资源及其多样性差异明显。研究表明，本河段鱼类群落组成简单，生态脆弱性较高，种群资源一旦遭到破坏，将很难恢复。且大部分土著鱼类为珍稀濒危和特有鱼类，保护意义重大。同时，大渡河上游鱼类正面临严重的外来鱼类入侵威胁，需引起高度关注。研究结果可为梯级开发对鱼类资源的影响评估提供基础资料，为鱼类栖息地保护等水生态保护措施的规划和设计提供依据。     

黑水河鱼类优先保护次序的定量分析

在金沙江下游干流大规模水电开发的背景下,干流开发与支流保护是生态环境保护的有效措施;黑水河是白鹤滩库区鱼类的优先保护支流,确定其鱼类优先保护次序和保护物种是进行鱼类栖息地修复和保护工作的首要任务和前提基础。在野外调查和查阅相关文献资料的基础上,运用濒危系数、遗传价值系数和物种价值系数对黑水河35种鱼类进行优先保护次序的定量分析,并结合黑水河栖息地实际情况,确定保护目标鱼类。结果显示,达到黑水河一级保护的鱼类只有1种,为长江上游特有鱼类长薄鳅（Leptobotia elongata）;达到二级保护的种类有12种,其中昆明裂腹鱼（Schizothorax grahami）、黄石爬鮡（Euchiloglanis kishinouyei）、短须裂腹鱼（Schizothorax wangchiachii）和长鳍吻鮈（Rhinogobio ventralis）为长江上游特有鱼类;处于三级保护的鱼类有17种,其中钝吻棒花鱼（Abbottina obtusirostris）和张氏?（Hemiculter tchangi）是长江上游特有鱼类;四级保护鱼类有5种,其中短体副鳅（Paracobitis potanini）为长江上游特有鱼类,评价结果基本反映了黑水河鱼类的实际情况。结合白鹤滩水库蓄水后黑水河栖息地生境改变的情况,最终确定昆明裂腹鱼、黄石爬鮡、短须裂腹鱼为黑水河栖息地修复和保护的目标鱼类,长薄鳅和长鳍吻鮈为备选保护鱼类。     

雅鲁藏布江中游桑日至加查江段渔业资源群落结构特征

2018年春季(4月)和秋季(10月)在雅鲁藏布江中游桑日至加查江段设9处采样点,其中干流7个,支流2个,采用定置刺网、地笼和肩背式电捕三种捕捞方式,调查了该江段的渔业资源。结果表明:(1)在调查水域共采集到渔获物14种,其中土著种类9种,主要由裂腹鱼类、高原鳅类和?科鱼类等3大类组成,外来鱼类5种,即鲤Cyprinus carpio、鲢Hypophthalmichthys molitrix、鲫Carassius auratus、鲇Silurus asotus和黄?Hyeleotris swinhonisps;(2)拉萨裸裂尻鱼Schizopygopsis younghusbandi分布范围较广,双须叶须鱼Ptychobarbus dipogon、尖裸鲤Oxygymnocypris stewartii和黑斑原?Glyptosternum maculatum分布较窄;(3)加查峡谷上下和峡谷内江段的渔获物种类有所不同,峡谷上江段鱼类种类最为丰富,且外来鱼类仅发现于峡谷上干流泽当江段;(4)调查水域干流主要分布有大个体的鱼类,支流主要分布小个体的鱼类,如拉萨裸裂尻鱼的幼鱼和小型鱼类高原鳅类,因此,桑日曲和沃卡河等支流不适合作为雅鲁藏布江干流桑日至加查江段鱼类的替代生境;(5)异齿裂腹鱼Schizothorax oconnori、拉萨裸裂尻鱼和拉孜裂腹鱼Schizothorax waltoni为调查水域中的优势种。本文首次调查了藏木水电站建成后加查峡谷及其上下水域的鱼类群落结构,可为分析加查峡谷桑日至加查江段梯级电站建成后对雅鲁藏布江中游鱼类的影响提供数据参考。     

梯级开发下金沙江下游鱼类群落结构特征及环境驱动因子

为了探明梯级电站开发下金沙江下游鱼类群落的结构特征及主要环境驱动因子，于2017年对春季和秋季金沙江下游尚未建成的乌东德和白鹤滩水电站江段以及已下闸蓄水的溪洛渡和向家坝水电站江段应用多网目复合刺网进行了鱼类群落定量研究，同时运用多种统计分析方法分析了鱼类多样性特征以及鱼类群落与环境因子的关系。研究发现仍保持正常流水未成库区的乌东德和白鹤滩江段鱼类群落与已成库区的溪洛渡和向家坝江段有着明显的差异。在仍为峡谷激流型生境的江段，鱼类组成以土著特有鱼类为主，优势种为喜流水的圆口铜鱼C. guichenoti、泉水鱼P. procheilus、犁头鳅L. fimbriata；而在已蓄水的库区江段，鱼类组成多为长江中下游常见种类，优势种为喜静水缓流的?H. leucisculus、飘鱼P. sinensis、似鱎T. wwinhonis。应用典范对应分析对鱼类群落与环境因子做了相关分析，发现影响金沙江下游鱼类群落的主要环境驱动因子包括水深、总固体悬浮物、电导率、pH和水温等。这些研究结果为制定金沙江下游鱼类种质资源和生物多样性保护的相关管理政策提供了基础与支撑。     

银盘电站蓄水前后乌江下游产漂流性卵鱼类早期资源变化

为了探究水电开发对流域鱼类资源的影响，遏制生物多样性衰退的趋势，2009-2015年5-7月对乌江下游干流漂流性鱼卵进行阶段性调查，初步分析银盘电站蓄水前后产漂流性卵鱼类的自然繁殖变化。结果表明，调查期间共采集到鱼卵12种，包括犁头鳅（Lepturichthys fimbriata）、中华金沙鳅（Jinsha sinensis）、中华沙鳅（Botia superciliaris）、圆筒吻鮈（Rhinogobio cylindricus）、吻鮈（Rhinogobio typus）、长鳍吻鮈（Rhinogobio ventralis）、蛇鮈（Saurogobio dabryi）、花斑副沙鳅（Parabotia fasciata）、铜鱼（Coreius heterodon）、中华倒刺鲃（Spinibarbus sinensis）、翘嘴鲌（Culter alburnus）和蒙古鲌（Culter mongolicus）。漂流性鱼卵年资源量为1012.99万~18673.97万粒，鱼类产卵场自上而下分布有彭水、高谷、江口（杨家沱）、武隆（石鼻子）、土坎（桃子沟）、羊角6处。银盘电站蓄水后，乌江下游产漂流性卵鱼类的自然繁殖较蓄水前发生了显著变化。种类组成中，典型的流水生境繁殖类群减少，缓静水生境繁殖类群增加；产卵规模显著下降，以长鳍吻鮈、铜鱼、圆筒吻鮈、中华金沙鳅的减少尤为显著；产卵场减少并逐步往坝下压缩，数量由6处减少到3处，长度由35 km减少到18 km，位于银盘库区的彭水、高谷产卵场消失，江口产卵场规模显著减少。产漂流性卵鱼类的大规模产卵都在涨水时发生，不同种类产卵对水文条件的要求有所差异，大坝建设引起的栖息地萎缩和水文情势改变是导致乌江下游漂流性卵鱼类早期资源衰退的主要原因。建议采用水库生态调度补偿措施，通过合理下泄生态流量，加大脉冲流量和流水江段长度来满足重要鱼类的繁殖和早期发育需求，并结合人工增殖放流、鱼类基础监测和生态学研究等综合手段，强化乌江下游鱼类资源的生态修复。     

银盘电站蓄水前后乌江下游产漂流性卵鱼类自然繁殖变化

为了探究水电开发对流域鱼类资源的影响,遏制生物多样性衰退的趋势,2009-2015年5-7月对乌江下游干流漂流性鱼卵进行阶段性调查,初步分析银盘电站蓄水前后产漂流性卵鱼类的自然繁殖变化。结果表明,调查期间共采集到鱼卵12种,包括犁头鳅(Lepturichthys fimbriata)、中华金沙鳅(Jinsha sinensis)、中华沙鳅(Botia superciliaris)、圆筒吻鮈(Rhinogobio cylindricus)、吻鮈(Rhinogobio typus)、长鳍吻鮈(Rhinogobio ventralis)、蛇鮈(Saurogobio dabryi)、花斑副沙鳅(Parabotia fasciata)、铜鱼(Coreius heterodon)、中华倒刺鲃(Spinibarbus sinensis)、翘嘴鲌(Culter alburnus)和蒙古鲌(Culter mongolicus)。漂流性鱼卵年资源量为1 012.99万～18 673.97万粒,鱼类产卵场自上而下分布有彭水、高谷、江口(杨家沱)、武隆(石鼻子)、土坎(桃子沟)、羊角共6处。银盘电站蓄水后,乌江下游产漂流性卵鱼类的自然繁殖较蓄水前发生了显著变化。种类组成中,典型的流水生境繁殖类群减少,缓静水生境繁殖类群增加;产卵规模显著下降,以长鳍吻鮈、铜鱼、圆筒吻鮈、中华金沙鳅的减少尤为显著;产卵场减少并逐步往坝下压缩,数量由6处减少至3处,长度由35 km减少至18 km,位于银盘库区的彭水、高谷产卵场消失,江口产卵场规模显著缩小。产漂流性卵鱼类的大规模产卵都在涨水时发生,不同种类产卵对水文条件的要求有所差异,大坝建设引起的栖息地萎缩和水文情势改变是导致乌江下游漂流性卵鱼类早期资源衰退的主要原因。建议采用水库生态调度补偿措施,通过合理下泄生态流量,加大脉冲流量和流水江段长度来满足重要鱼类的繁殖和早期发育需求,并结合人工增殖放流、鱼类基础监测和生态学研究等综合手段,强化乌江下游鱼类资源的生态修复。     

怒江傈僳族自治州的鱼类调查

为了保护怒江州的鱼类资源,按照<内陆水域渔业资源调查手册>要求,于2006年1月至2007年底开展怒江州鱼类资源调查.调查范围涉及全州29个乡(镇)中的28个,覆盖了怒江州的内怒江、澜沧江、伊洛瓦底江3大水系的干流和主要支流.云南省怒江傈僳族自治州现有鱼类72种;其中,土著鱼类58种,隶属5目、8科、32属;分析了鱼类组成区系和分布特点,并提出了保护鱼类资源的初步建议.     

北盘江光照水电站建设前后鱼类资源变化

2009年9月和2010年5月,对北盘江光照水电站影响河段鱼类资源进行现场调查,采集鱼类45种,其中18种为新记录种,各河段鱼类组成特点与生态类型相符。结合相关文献资料,确定调查河段鱼类共71种,其中珍稀濒危鱼类4种,珠江水系特有鱼类3种。光照电站的建设对库区河段的鱼类资源影响显著,喜静缓流生境鱼类占76.5%,喜急流或流水生境鱼类占23.5%;流水生境河段受影响较小,约90%鱼类喜流水生境。调查水域没有典型产漂流性卵鱼类的产卵生境,原记录的产粘性卵鱼类产卵场受影响较小。     

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.     

Production of diatom–bacteria biofilm isolated from Seriola lalandi cultures for aquaculture application

Controlled incorporation of selected microalgae and bacteria in aquaculture systems can be beneficial because they can act as microbiological control. That is why the characteristics of biofilm generated naturally in Seriola lalandi culture cages were analysed, their potential benefit to the growth of larvae was studied, and their controlled use for improving the larval viability and as a vector to improve incorporation of previously studied probiotic bacteria was tested. According to biodiversity results, these biofilms are composed of a diatom–bacteria mix showing a decrease in biodiversity in laboratory culture conditions being dominated by Navicula phyllepta and bacteria of the family Rhodobacteraceae. This can be produced on mesh substrates incorporated in bioreactors with rapid growth rate and adhesiveness. Preliminary results from the addition of substrates with this specific biofilm in larvae culture systems showed that it is consumed by the larvae without negative effects, while positive effects on the viability of larvae in combination with probiotics were observed. Considering preliminary results, the addition of these specific substrates with diatom–bacteria biofilms could be a good improvement for aquaculture systems and together with the use of probiotics can contribute to maintaining a stable and controlled system improving the viability of the larval fish culture in its early stages.