凡纳滨对虾EST微卫星标记初步筛选

对161 075条凡纳滨对虾dbEST(database of “Expressed Sequence Tags”)的数据进行SSR序列筛选,搜索参数为二~六核苷酸重复6次以上(包括6次),共获得含SSR的EST序列12 600条,占整个凡纳滨对虾dbEST数据库的7.8%,其中二核苷酸重复10 104条,占总ESTSSR序列的80.2%; 三核苷酸重复2 036条(16.1%),四核苷酸重复336条(2.7%),五核苷酸重复35条(0.3%),六核苷酸重复89条（0.7%）。大部分发现的微卫星序列为完美型(perfect)的重复序列。在二核苷酸所获得的SSR重复单元中,AG/CT是优势重复单元,共分布4 820条,占二核苷酸各重复单元的47.8%;其次是AC/GT重复,共分布3 584条,占二核苷酸各重复单元的35.4%;最后是AT/TA 和CG/GC,分别占二核苷酸各重复单元的16.6%和0.2%。通过对凡纳滨对虾EST序列中SSR位点信息的发掘分析,共设计77对微卫星引物,在10个个体中成功扩增的引物有54对,成功扩增率为70.1%。其中多态性丰富的引物28对,多态率为51.9%。等位基因数为2～5,PCR产物大小为140～600 bp。本研究筛选的ESTSSR标记将为凡纳滨对虾的分子遗传学研究、种质鉴定等提供可靠的工具。     

三疣梭子蟹微卫星富集文库的构建与群体遗传分析

采用富集文库-菌落原位杂交法分离了30个三疣梭子蟹(Portunus trituberculatus)的微卫星标记.三疣梭子蟹基因组DNA经HaeⅢ酶切连接后.用固定了((AC)15和(AG)15探针的尼龙膜((Hybond N+)捕捉含有微卫星的片段.转化至大肠杆菌DH5α中.构建三疣梭子蟹微卫星富集文库.菌落原位杂交后.任意选取150个克隆进行测序.阳性克隆率为85.48%.利用软件设计了105对微卫星引物.筛选到稳定扩增标记56对.采用30个三疣梭子蟹个体进行多样性评价.30个位点均表现出多态性.观测杂合度(Ho)、期望杂合度(He)及多态性信息含量(PIC)的范围分别为0.2222～1.000 0、 0.4367～0.9099和0.350～0.892.本研究筛选的微卫星位点将为下一步三疣梭子蟹遗传多样性分析、家系分析、遗传图谱构建和QTL定位等研究提供基础依据.     

军曹鱼全基因组微卫星特征分析与多态性标记的筛选及应用

为更好地开发军曹鱼(Rachycentron canadum)高多态性微卫星分子标记，本研究基于军曹鱼全基因组测序结果，利用MISA1.0软件对其简单重复序列(simple sequence repeat, SSR)的位点信息进行检索及分析。结果显示，基因组中共筛选出1~6个核苷酸为重复单元的SSR位点344 820个，其中，以单核苷酸重复序列最多(174 146个)，占SSR总数的50.50%；其次为二核苷酸重复和三核苷酸重复序列，分别占SSR总数的30.23%和14.02%。在SSR包含的重复单元中，单核苷酸重复以A/T类型为主，AC/GT是二核苷酸的优势重复单元类型。军曹鱼基因组SSR核心序列重复次数在4~275次范围内波动，单核苷酸SSR重复数为10的最多，二核苷酸SSR重复次数为6的最多。本研究设置长度≥12 bp为筛选高多态性SSR位点的标准，共获得361 684个位点。在上述位点中随机选取100个候选位点进行基因分型检测，利用从中筛选到多态性较高的10个SSR标记分别对北海、陵水、硇洲、徐闻和三亚5个养殖群体进行遗传多样性分析，145尾个体中共检测到69个等位基因，观测杂合度(Ho)、期望杂合度(He)和多态信息含量(PIC)平均值分别为0.628、0.706和0.653。相关研究表明，军曹鱼基因组中SSR位点类型较为丰富、多态性潜能较高，从中筛选获得的多态性SSR标记可为军曹鱼分子标记辅助育种、群体遗传多样性评价等研究提供有力支持。     

大黄鱼EST微卫星标记初步筛选

通过构建大黄鱼性腺线性化cDNA文库，并经测序后获得3535条EST，对其二碱基至六碱基重复序列进行筛选，共发现微卫星位点150个，占EST序列的4．24％；其中包括二碱基重复序列64条，三碱基重复序列80条，四碱基重复序列5条，五碱基重复序列1条；三碱基重复序列是最丰富的重复单元，占53．3％。在这些微卫星序列中，（TG／GT／AC／CA）n形式在二碱基重复中最为常见，（GAG／AGG／GGA／CCT）n形式在三碱基重复序列中最为常见，分别占微卫星序列总数的26％和14％。选取其中的62条微卫星序列进行引物设计、合成与多态性检测，经过PCR扩增，2．0％的琼脂糖凝胶电泳检测，获得呈多态性微卫星引物8对，多态率为12．9％。本研究为开发大黄鱼EST微卫星分子标记和大黄鱼基因编码区微卫星的功能研究提供有价值的信息。     

基于RAD-seq技术的长体圆鲹二、三核苷酸重复微卫星标记开发与评价

通过对长体圆鲹(Decapterus macrosoma)基因组进行RAD-Seq高通量测序,共获得58 180条微卫星序列,选取112条二、三核苷酸重复的微卫星序列设计引物,经筛选后,共获得27个具有多态性的微卫星标记。利用一个长体圆鲹群体对通过筛选的微卫星标记的种群遗传学特征进行评价。结果显示,27对引物扩增的序列中18个位点为二核苷酸重复,重复次数为9～14次,9个位点为三核苷酸重复,重复次数为6～10次,等位基因数(Na)为5～17 (平均10.6),表观杂合度(Ho)为0.342 9～0.857 1 (平均0.631 7),期望杂合度(He)为0.538 3～0.911 8(平均0.796 8),多肽信息含量(PIC)为0.497～0.886 (平均0.780 9),除1个位点外,其他位点PIC值均大于0.500,表明开发的微卫星位点具有较高的多态性。"哈迪-温伯格"平衡(HWE)检测结果显示,19个标记等位基因频率符合HWE。连锁不平衡检测表明各位点间无连锁不平衡现象。该研究开发的27个微卫星标记可为长体圆鲹种群遗传学研究提供基础。     

三疣梭子蟹多态性微卫星DNA标记的筛选及评价

根据前人FIASCO方法构建的三疣梭子蟹微卫星富集文库,对含微卫星的DNA序列设计了71对引物并对其进行了多态性筛选,筛选出21对多态的微卫星引物,对三疣梭子蟹1个野生群体的30个个体进行遗传多样性检测,同时对引物进行评价。21个位点共获得了188个等位基因,平均每个位点扩增得到8.9个等位基因。不同引物获得的等位基因数差异较大,从3～13个不等,其中Pot8、Pot37、Pot48、Pot53、Pot54、Pot66六个位点分别获得了11、12、12、11、13、11个等位基因,而Pot46仅获得了3个等位基因。等位基因的大小分布在131～312bp,基本符合引物设计时理论产物长度。21个微卫星位点的期望杂合度的范围为0.659～0.889,PIC值均高于0.5,表明它们都有很高的杂合度,均可用于三疣梭子蟹种群遗传结构分析,为三疣梭子蟹品种选育、种系评估提供更多的微卫星DNA信息。     

放流三疣梭子蟹遗传多样性和贡献率初步研究

近年来我国沿海三疣梭子蟹自然资源明显下降,为恢复现有资源,辽宁省自2012年开始,连续实施了4年大规模人工放流工作。在目前的增殖放流中,为检测参与繁殖的三疣梭子蟹亲本和即将放流的子代间的遗传差异以及亲本对其子代的繁殖贡献率水平,利用10对具有丰富遗传多态性的微卫星分子标记,分别对9只三疣梭子蟹雌性亲本和179只即将放流的子代进行了遗传多样性分析及亲子鉴定。结果发现,子代的平均观测杂合度、平均期望杂合度和平均多态性信息含量数值均低于参与繁殖的雌性亲本,亲本和放流子代之间在观测杂合度、多态性信息含量参数方面并无显著差异(P0.05),但期望杂合度遗传参数存在显著差异(P0.05),子代的遗传多样性较雌性亲本呈下降的趋势。使用4个微卫星分子标记时,累积排除率≥0.998,亲子鉴定的准确率为56.98%;微卫星分子标记为6个时,累积排除率≥0.9999,准确率达到97.21%;当使用8个微卫星分子标记鉴定时,准确率达100%。同时发现,9只雌性亲本对子代均有贡献,最高为29.61%,最低为3.35%,不同亲本之间的贡献率存在显著差异(P0.05)。研究表明,微卫星可以作为有效的标记手段用于三疣梭子蟹增殖放流遗传评估中。上述试验结果将为我国三疣梭子蟹增殖放流的科学发展提供基础资料。     

从中国对虾ESTs中筛选微卫星标记的研究

利用生物信息学方法在含有10446个中国对虾ESTs的数据库中进行微卫星序列的筛选，共发现微卫星序列229个，占整个ESTs数据库的2．19％，其中含双碱基重复序列146个和3碱基重复序列58个，分别占在ESTs数据库中发现微卫星序列总数的63．76％，和25．33％，大部分发现的微卫星序列均为Perfect形式的重复序列。根据筛选得到的微卫星序列设计并合成引物19对进行多态性检测，在有扩增产物的16对引物中，首次筛选得到8个中国对虾微卫星标记，并对这些微卫星标记进行了等位基因频率、观测杂合度、期望杂合度、PIC值等统计学指标的评价。结果表明，在8个微卫星位点上，等位基因的数目从5到15不等，等位基因长度从：165～305bp，期望杂合度和多态性信息含量分别为0．59到0．89和0．56到0．88，表明这8个中国对虾微卫星标记完全适合于遗传分析。     

基于线粒体COⅠ基因序列的三疣梭子蟹东海区群体遗传多样性分析

通过对分布在东海区远海区(济州岛海域)和近海区(长江口以南和以北海域)的三疣梭子蟹(Portunus trituberculatus)自然群体线粒体COⅠ基因部分序列的测定,比较并分析了其群体遗传多样性和遗传结构。在24个采集点共286个样本的线粒体COⅠ序列中共检测到45种单倍型,单倍型多样性为0.864;核苷酸多样性为0.002 84,平均核苷酸变异数是1.686,其中有23个单倍型为单个采集点所独享,Hap3出现频率最高,在23个采样点的83个样本中均有发现,是所有三疣梭子蟹样本的共享中心单倍型。群体遗传多样性分析显示,远海区群体的遗传多样性水平最高,其次为长江口以北群体,长江口以南群体最低。由群体间遗传距离、系统进化树和单倍型网络关系图发现,东海区海域三疣梭子蟹种群间存在基因交流,亲缘关系的远近不以地理位置的远近为依据;AMOVA分子方差分析结果显示,三疣梭子蟹的遗传变异主要来自群体内,而群体间无显著遗传分化,不存在明显的地理趋势。     

基于胡鲇科和鲇科ESTs序列初步筛选兰州鲇EST-SSR分子标记

利用SSRHunter软件对现已公布的鲇形目(Siluriformes)中胡鲇科(Clariidae)和鲇科(Siluridea)共2002条EST(Expressed Sequence Tag)序列筛选兰州鲇(Silurus lanzhouensis)微卫星标记,并分析其序列丰度和分布特征。结果共发现209个微卫星序列,占整个ESTs数据库的10.44%;其中三碱基重复序列数量最多,占ESTs数据库中发现微卫星序列总数的35.62%;二、四、五、六碱基重复序列分别占微卫星序列总数的28.31%、25.57%、7.76%、2.74%。根据侧翼序列,设计125对引物,随机选取58对进行扩增鉴定及多态性筛选。结果显示29对引物能稳定扩增,16对引物具有多态性,每个位点等位基因数2~7个(平均3.75),观测杂合度(Ho)0.133 2~0.732 2(平均0.405 1),期望杂合度(He)0.198 2~0.848 3(平均0.560 2),多态信息含量(PIC)0.124 1~0.794 5(平均0.506 5)。研究表明,借用已有鲇形目鱼类ESTs数据库筛选到的兰州鲇微卫星标记质量较好,可为兰州鲇种质资源保护、微卫星连锁图谱构建、经济性状的QTL定位及分子标记辅助育种奠定基础。     

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.