七连屿珊瑚礁鱼类种类组成特征分析

为了更好地了解和保护西沙群岛七连屿珊瑚礁生态系统和珊瑚礁鱼类,本研究综合2018-2020年的调查结果及历史资料表明,七连屿珊瑚礁海域目前共发现珊瑚礁鱼类315种,区域物种密度为12.6种/km2.七连屿珊瑚礁鱼类隶属于12目49科,以鲈形目(Perciformes)鱼类最多,占总种类数的79.05％;其中28科鱼类(...     

南海珊瑚礁海域鱼类分类多样性大尺度分布格局

珊瑚礁区生物多样性是当今生态学研究热点之一,为更全面地了解南海诸岛珊瑚礁海域鱼类物种多样性分布格局,系统整理了20世纪70年代以来南海东沙、西沙和中沙及南沙群岛珊瑚礁海域鱼类资源调查的历史资料,研究了南海珊瑚礁鱼类分类学多样性.种类统计结果表明,目前东沙记录鱼类种类514种,西沙和中沙632种,南沙548种;各礁区记录鱼类物种数目少于预测数目,也少于全球其他生境相似的海域记录的鱼类种数.估算了南海珊瑚礁鱼类平均分类差异指数△+和分类差异变异指数∧+,结果显示,东沙△+和∧+分别为55.1、121;西沙、中沙△+为60.2,∧+为164;南沙△+为56.6、∧+为150;各礁区海域鱼类△+值均小于东海陆架海域,而∧+值均高于东海陆架海域.在种和科的分类水平上,计算了南海珊瑚礁海域与卡拉棉群岛、米尔恩湾、南沙群岛西南陆架和南海北部陆架海域鱼类的相似性系数,结果表明,西、中沙群岛与其他礁区海域鱼类在种级分类阶元上的相似性系数相差较大,所有珊瑚礁海域鱼类在科级分类阶元上的相似性系数较为接近;另外,所有珊瑚礁海域鱼类种(科)间相似性均高于其与陆架海域鱼类种(科)间相似性.对南海珊瑚礁、卡拉棉群岛和米尔恩湾等海域典型礁栖性鱼类的科的物种相对丰富度进行了Kruskal-Wallis检验,结果表明,其差异均不显著(P＞0.05).结论认为,物种多样性较高而分类多样性较低是南海珊瑚礁鱼类多样性大尺度分布格局的主要特征.     

南沙群岛渚碧礁鱼类分类多样性研究

根据1999-2018年南沙群岛渚碧礁礁栖鱼类流刺网和手钓调查资料,分析了渚碧礁礁栖鱼类物种组成及分类多样性,计算了其平均分类差异指数(Δ^+)及分类差异变异指数(Λ^+)。结果显示,渚碧礁礁区共记录礁栖鱼类11目43科93属152种,其中鲈形目鱼类占绝对优势(76%);渚碧礁鱼类的Δ^+为58.75,Λ^+为102.60。与国内外其他生态系统鱼类群落组成的对比发现,渚碧礁鱼类的Δ^+高于赵述岛、米尔恩湾和圣何塞岛,低于东海陆架、南沙群岛西南陆架、北部湾和大亚湾,而Λ^+则均低于其他群岛。研究表明渚碧礁鱼类群落物种间的亲缘关系比东海陆架、南沙群岛西南陆架、北部湾和大亚湾更为接近,但比赵述岛、米尔恩湾和圣何塞岛远。物种多样性较高而分类多样性较低是渚碧礁礁栖鱼类多样性分布格局的主要特征。但该礁易受到人类活动的干扰,应及时给予保护。     

海南岛东岸、南岸浅水礁区近10年珊瑚礁鱼类种类分布及多样性探讨

根据2004—2013年海南岛东岸、南岸浅水礁区珊瑚礁鱼类监控数据,利用截线样条法、分类学多样性指数、相对丰富度及相似性指数等方法技术对海南岛东岸、南岸浅水礁区珊瑚礁鱼类种类组成及生物多样性进行研究。结果显示,海南东岸、南岸浅水礁区近10年调查珊瑚礁鱼类共计6目32 科64属130种,其中鲈形目居绝对优势;珊瑚礁鱼类密度大致呈现由南向北逐渐递减的趋势;科级多样性平均值为4.41,属级多样性指数平均值为3.09,标准化的G-F指数平均值为0.30;鲈形目珊瑚礁鱼类相对丰富度占有绝对优势,相对丰富度较高的6个科分别为雀鲷科、隆头鱼科、蝴蝶鱼科、天竺鲷科、四齿鲀科及玻甲鱼科;珊瑚礁鱼类在目级极为相似,相似性指数在0.86～1之间;科、属、种级相似性指数较低,均在0.5以下,通过Jaccard's种类相似性指数分析,海南岛东岸、南岸珊瑚礁鱼类种类较多,物种丰富。珊瑚礁鱼体长范围6～10 cm区间的数量最多,其次为0 ～5 cm区间,21～40 cm区间的珊瑚礁鱼类在浅水礁区分布极少。本研究通过对海南岛东岸、南岸浅水礁区珊瑚礁鱼类近10 a的种类分布及多样性进行探讨,旨在为海南岛珊瑚礁生态系统及珊瑚礁鱼类保护与研究提供基础数据及理论依据。     

南海美济礁瀉湖区鱼类优势种和生物多样性的长期变化

珊瑚礁鱼类是诊断和修复退化珊瑚礁新方法的关键组分。为了解环境变化和人类活动胁迫下南海典型珊瑚礁鱼类组成和多样性的演变趋势, 本研究根据 1998—2018 年美济礁瀉湖区鱼类手钓和刺网调查数据, 对南海美济礁瀉湖区鱼类种类组成、优势种和物种多样性指数的长期变动进行研究。结果表明, 与 1998—1999 年相比, 2012— 2018 年美济礁瀉湖区鱼类组成和优势种更替明显, 鹦嘴鱼科(Scaridae)、刺尾鱼科(Acanthuridae)、蓝子鱼科(Siganidae) 等具有重要生态功能的鱼类消失或明显减少; 优势种数目下降, 但其优势度显著增加, 第 1 优势种的相对优势度和所有优势种的平均优势度均明显增加; 1998—2018 年采集单位鱼类种类数所需的捕捞努力量和样本量均明显稳定增加; 手钓努力量增加对相应物种多样性指数增加有明显影响, 刺网努力量增加对多样性指数增加影响不明显; 刺网采样方式评估美济礁鱼类物种多样性比手钓采样方式更稳健; 基于刺网鱼类样本, 与 1999 年 5 月相比, 2016— 2018 年美济礁瀉湖区鱼类物种多样性极显著降低。结论认为, 人类捕捞和美济礁有效生境面积下降而导致的生态系统承载力下降是鱼类种类或丰度减少及多样性降低的主要原因。为促进南海美济礁鱼类资源恢复和保护, 建议及时采取措施保护其资源, 改善栖息地质量。     

长江中游监利江段鱼类早期资源及生态调度对鱼类繁殖的影响

为了解三峡水库开展试验性生态调度后长江中游监利江段鱼类早期资源现状,本研究于2018年、2019年的5—7月对该江段卵苗种类组成、资源量、产卵场及生态水文指标开展了调查,共鉴定出鱼类7目14科54种（属）,其中产漂流性卵鱼类26种。仔鱼组成以贝氏䱗（）（占15.2%）、沙鳅属（粒、324.2×10⁸尾;2019年分别为35.9×10⁸粒、1140.7×10⁸尾。监利江段成为鳊（）等鱼类的重要产卵场。生态调度对监利江段贝氏䱗、鳊、银鮈等鱼类的自然繁殖有明显促进作用。产卵量与涨水持续时间、流量累积涨幅呈正相关。监利江段涨水持续时间4 d及以上,流量累积涨幅3500 m³/s及以上时,产卵量可占当年调查期间鱼卵总规模的8.4%以上。建议继续开展并优化生态调度,加强对监利江段鱼类早期资源的基础研究。     

东沙群岛珊瑚礁海域鱼类物种分类多样性研究

根据南海东沙群岛珊瑚礁海域鱼类物种种类组成的历史资料,系统整理了鱼类物种组成,并计算了东沙海域的平均分类差异指数(△+)和分类差异变异指数(∧+).结果显示,东沙珊瑚礁海域共记录鱼类18目,68科,173属,403种,鲈形目鱼类占绝对优势.△+约为55.2,低于黄、渤海、长江口和东海陆架海域(P＜0.01),∧+约为110,低于黄、渤海、长江口(P＜0.01)和东海陆架海域(P>0.05).大尺度上,一般纬度越低,中国海洋鱼类△+越小,表明珊瑚礁鱼类群落物种的亲缘关系要比陆架和河口区域的接近.     

西沙群岛珊瑚礁海域鱼类分类学多样性

为评价南中国海西沙群岛珊瑚礁海域鱼类分类学多样性和更好地保护其鱼类,根据西沙群岛珊瑚礁海域鱼类物种组成的历史资料对西沙群岛及其16座岛礁的珊瑚礁水域鱼类物种数目、平均分类差异指数和16座岛礁的G-F多样性指数作了分析。结果显示,西沙共记录鱼类661种,隶属于25目、93科、305属。其中,永兴岛(351种),华光礁(173种),东岛(160种)记录鱼类物种数目较多。西沙鱼类平均分类差异指数(Δ⁺)约为60.2,各岛礁的Δ⁺与物种数目无关。中建岛、晋卿岛、玉琢礁等岛礁鱼类平均Δ⁺显著低于西沙鱼类Δ⁺。西沙鱼类Δ⁺小于陆架和河口区鱼类Δ⁺,说明珊瑚礁海域鱼类亲缘关系比陆架和河口区域的都要接近,此外大尺度上,一般纬度越低,中国海洋鱼类Δ⁺越小。但G-F多样性测度各指数由物种数目的大小决定,一般物种数目较大的岛礁G-F多样性各指数也相对较高,而R_G-F指数更适合该海域鱼类多样性的测度。以石岛为例初步探讨了G-F指数为负的原因,一是物种数目较少,二是多样性测度的关键函数Y=-XLnX并不是单调函数所致;物种数目较大的岛礁如永兴岛、华光礁、东岛等应该成为西沙珊瑚礁海域鱼类保护的重点区域。     

漳河山西段鱼类和大型底栖动物群落结构特征

2017年对漳河山西段鱼类、大型底栖动物进行调查,分析物种组成、多样性及空间差异特征。结果显示：(1)共采集到鱼类24种,优势种为棒花鱼Abbottina rivularis (Basilewsky, 1855)、麦穗鱼Pseudorasbora parva (Temminck et Schlegel, 1846)、拉氏大吻鱥Rhynchocypris lagowskii (Dybowski, 1869)、高体鳑鲏Rhodeus ocellatus (Kner, 1867)、中华鳑鲏Rhodeus sinensis Günther, 1868、子陵吻鰕虎鱼Rhinogobius giurinus Rutter, 1879;大型底栖动物44种,年平均密度为256个/m_²,优势种为中华锯齿米虾Neocaridina denticulate sinensis Kemp、蜉蝣科稚虫Ephemeridae、扁蜉科稚虫Heptageniidae、椭圆萝卜螺Radix swinhoei H.Adams。(2)各采样河段鱼类Shannon-Wiener指数、Margalef指数平均值分别为1.53、1.68,夏季多样性好于春、秋季;大型底栖动物两个多样性指数平均值分别为1.14、1.47,春季多样性好于夏、秋季。(3)聚类分析结果显示,鱼类组成分为清漳河、浊漳河两组,清漳河鱼类指示物种包括短须颌须鮈Gnathopogon imberbis (Sauvage et Dabry, 1874)、拉氏大吻鱥Rhynchocypris lagowskii (Dybowski, 1869),浊漳河指示物种为鳑鲏属Rhodeus的鱼类;大型底栖动物组成同样分为清漳河、浊漳河两组,清漳河平均密度及物种数低于浊漳河,其昆虫纲蜻蜓目物种数多于浊漳河,而昆虫纲龙虱科、蝎蝽科、黾蝽科、鱼蛉科以及甲壳纲、腹足纲、双壳纲、寡毛纲、蛭纲的物种数少于浊漳河。底栖动物物种结构的差异受流域内营养物质输入以及水环境质量的影响较大。     

曹娥江流域鱼类资源调查

近三十年来曹娥江流域水利工程建设、水域环境、渔业捕捞等影响鱼类生存的环境因素发生了较大的改变,迫切需要对流域内的鱼类资源现状重新进行调查研究。本研究于 2015~2018 年对曹娥江流域 9 个采集点的鱼类资源进行调查分析。结果表明,调查共获得鱼类 105 种,隶属于 13 目 26 科。其中,鲤形目种类最多,为 65 种,占总种类数的 61.90%,优势种为鲢、麦穗鱼和子陵吻虾虎鱼。曹娥江水域鱼类群落Shannon–Wiener多样性指数（H''）为 1.9718,Simpson优势度指数（λ）为 0.3297,Pielou均匀度指数（J''）为 0.4237,Margalef种类丰富度指数(D)为 10.5741。与《浙江省动物志?淡水鱼类》中记载的曹娥江鱼类调查结果比较,本次调查获得鱼类中肉食性鱼类比例减少,杂食性鱼类比例增加,同时 Shannon–Wiener多样性指数（H''）和Pielous均匀度指数（J''）下降。这一结果表明,与上世纪九十年代相比,近年来曹娥江流域鱼类群落结构的复杂性降低,其稳定性降低;鱼类生物多样性下降提示曹娥江鱼类资源正处在衰退之中。因此,曹娥江流域仍需采取有效措施,进一步加强流域内鱼类资源保护。     

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.