草鱼NADPH氧化酶2个调节亚基cDNA的克隆及表达特征

为了解草鱼(Ctenopharyngodon idellus)NADPH多酶复合体的基因结构及其在机体的防御体系中的功能,利用RT-PCR结合RACE-PCR的方法,克隆草鱼NADPH氧化酶的2个调节亚基p40phox和p47phox的cDNA,对其编码的氨基酸序列进行了同源性比较和功能域分析,同时对这两个亚基在草鱼不同组织中的差异性表达进行分析。结果显示:p47phox亚基cDNA序列全长为1 589 bp,开放阅读框长度为1 233 bp,编码410个氨基酸;p40phox亚基cDNA序列全长为2 103 bp,开放阅读框为1 068 bp,编码355个氨基酸。这两个亚基编码的氨基酸序列与其他鱼类的同源性在68%~96%,具有其它鱼类类似的PX,SH3,PB1和PC功能域。组织差异性表达分析结果表明:2个调节亚基在草鱼胸腺、心脏、头肾、鳃、肠、肝、肾、脾和皮肤组织中均有表达,在不同组织中的表达强度略有差异,在心脏、胸腺中表达水平最高,在肝脏中表达水平较低,但是不同组织之间的表达水平差异不显著(P>0.05)。     

剑尾鱼卵黄蛋白原C(Vg C)全长cDNA的克隆及表达

利用逆转录聚合酶链式反应(RT-PCR)和cDNA末端快速扩增(RACE)等方法,克隆获得剑尾鱼卵黄蛋白原C(Vg C)基因的全长cDNA序列。剑尾鱼Vg C基因cDNA序列全长4 011 bp,其5′非编码区包含12 bp和3′非编码区包含246 bp;含有一个3 753 bp的开放阅读框(ORF),编码1 250个氨基酸,推测其编码氨基酸分子量大小为141.7 ku,编码氨基酸序列与其他鱼类卵黄白原C编码氨基酸序列相似性在44%～85%。荧光定量PCR结果显示,Vg C在剑尾鱼肝脏中表达量最高,脾、肾、卵巢中有微量表达,脑、肌肉、鳃中几乎没有检测到表达;对不同时间暴露在雌激素中剑尾鱼肝脏进行实时荧光定量PCR表达分析的结果表明,Vg C在剑尾鱼肝脏中第5天表达量最高,随后降低,第9天后维持相对较低的表达量。研究首次克隆了剑尾鱼Vg C基因全长cDNA序列,并对Vg C在剑尾鱼体内表达组织器官分布及雌激素诱导后不同时间表达谱进行了初步研究,为剑尾鱼生殖生理及环境污染物监测应用等不同领域研究打下重要基础。     

鲤脂肪酸合成酶基因的克隆与表达分析

脂肪酸合成酶(FASN)是动物体内脂肪酸合成的关键酶。本研究利用逆转录PCR和RACE技术获得鲤Cyprinus carpio FASN全长cDNA序列为8 927bp,开放阅读框7 533bp,编码2 511个氨基酸。FASN蛋白质相对分子量274 145.67D,理论等电点(PI)为6.10。氨基酸同源性分析结果显示:鲤FASN基因与其他鱼类同源性为75.13%~95.34%,与人同源性为61.81%。系统进化树结果显示:鲤FASN氨基酸序列与金线鲃Sinocyclocheilus grahamia聚为一支,同源性最高。实时荧光定量PCR(RT-qPCR)检测结果表明:FASN基因鲤脑组织中表达量最高,肝脏次之,血液中最低。鲤FASN基因的获得为进一步深入研究鲤脂肪酸的合成途径及脂肪发育分子调控机制奠定了基础。     

军曹鱼Ig κ轻链cDNA克隆及组织表达分析

应用同源克隆和RACE技术克隆了军曹鱼(Rachycentron canadium Linnaeus)Igκ轻链的cDNA全序列,并分析其在组织中的表达.军曹鱼Igκ的cDNA全长969 bp,3'端的非编码区域(UTR)为188 bp,5'UTR为52 bp,开放阅读框为729 bp,编码242个氨基酸,分子量约为26.255 kD,理论等电点7.52.推测的军曹鱼Igκ恒定区氨基酸序列同鰤(Seriola quinqueradiata)、大西洋鲑(Salmo salar)的Ig轻链同源性最高,达77%以上,可变区氨基酸序列与鰤的相应序列同源性最高,达87%.通过构建系统进化树可以看出,军曹鱼Igκ恒定区氨基酸序列同鰤、大西洋鲑的L3、斑点叉尾鲴(Ictalurus punctatus)的G等鱼的轻链均为κ型的聚为一支,同大西洋鲑的L2、斑马鱼(Danio rerios)的L2、鲤(Cyprinus carpio)的L2等均为λ型的明显不同,由此可推断此序列属于Igκ型.利用半定量PCR技术,发现在健康鱼体中κ链基因在肝脏和鳃中的表达量较高,在肠和脑组织中几乎没有表达.经鲨鱼弧菌(Vibrio carchariae)JT2刺激192 h后,κ链基因在采样的各个组织中均有表达,尤其在头肾、肠、鳃和脾中的表达量较正常水平明显升高,而肝的表达量有所下降,脑组织有κ链基因的少量表达.说明经刺激后头肾、脾脏、肠、鳃是免疫球蛋白的主要表达场所,在抵御病原感染过程中发挥着重要作用.     

剑尾鱼 2 种卵黄蛋白原全长 cDNA 的克隆及序列分析

卵黄蛋白原是环境雌激素效应研究的重要生物标志物,广泛应用于水环境内分泌干扰物污染的评价。本研究利用RT-PCR和cDNA末端快速扩增法(RACE)克隆获得了剑尾鱼(Xiphophorus helleri)的2种卵黄蛋白原基因—VgA和VgB,并对其基因结构和系统进化进行分析。VgA基因cDNA序列全长5159bp,开放阅读框(ORF)5058bp,编码1685个氨基酸。VgB基因cDNA序列全长5349bp,开放阅读框(ORF)5067bp,编码1688个氨基酸。2种cDNA序列均具有与已发现的卵黄蛋白原分子相似的主要特征和功能域,包括Vitellogenin结构域、VWFD结构域和多聚丝氨酸区域,且与已知其他鱼类卵黄蛋白原基因有较高的同源性。     

大鳍鳠免疫球蛋白M 重链基因的克隆及表达分析

用RACE-PCR和RT-PCR方法获得大鳍鳠分泌型免疫球蛋白M(sIgM)重链基因的全长cDNA序列.大鳍鳠sIgM的cDNA全长为1 992 bp,包含5 '非编码区53 bp,3’非编码区226 bp,开放阅读框1 713,编码570个氨基酸.推测的大鳍鳠sIgM蛋白质序列可变区含有4个骨架区(FR)和3个互补决定区(CDR),恒定区(CH)含有CH1、CH2、CH3和CH4 4个部分.与其它6种硬骨鱼类IgM氨基酸序列比对分析表明,大鳍鳠sIgM存在半胱氨酸和色氨酸保守位点；其氨基酸序列与斑点叉尾鲴IgM的相似性最高,为54.3％；与石斑鱼的相似性最低,为24.6％.进化树分析表明,大鳍鳠sIgM与斑点叉尾鲴聚为一支.RT-PCR显示,大鳍鳠IgM基因主要在血细胞、脾脏、头肾和中肾中转录表达；注射嗜水气单胞菌后,血细胞、脾脏和头肾IgM重链基因转录表达量在1～10 d内有显著上升.     

虎皮鱼热激蛋白PtHsp70基因序列与低温表达分析

通过同源克隆和cDNA末端快速克隆技术扩增获得狭温热带鱼类虎皮鱼热激蛋白70(PtHsp70)基因的cDNA序列,BLAST比对分析基因序列同源性,预测其编码氨基酸序列和结构,实时荧光定量PCR技术分析虎皮鱼PtHsp70基因组织特异性表达谱和低温胁迫下PtHsp70基因的表达模式。研究结果表明,PtHsp70基因cDNA序列全长2317 bp,其中5′非编码区120 bp,3′非编码区266 bp,编码区1932 bp,对应的开放阅读框为121～2052 bp,预测编码643个氨基酸。PtHsp70基因mRNA在成年虎皮鱼不同组织中表达水平依次为肝脏肌肉鳃脑,其中肝脏PtHsp70基因本底表达水平显著高于其他组织(P0.01),表明其在肝脏中具有重要的生物学功能。而随温度降低,肝脏PtHsp70基因表达水平呈先降后升的趋势,表明肝脏PtHsp70基因参与虎皮鱼应对低温胁迫的过程;随温度降低,虎皮鱼脑、鳃和肌肉组织PtHsp70基因mRNA水平显著上调(P0.01),说明低温胁迫诱导PtHsp70基因mRNA表达。本研究克隆并鉴定了PtHsp70基因序列和组织表达谱,分析了低温胁迫下PtHsp70基因表达模式,研究结果显示,狭温热带鱼类虎皮鱼的PtHsp70基因具有组织特异性和温度诱导型表达特征。研究发现,PtHsp70基因在响应低温胁迫过程中具有重要作用,具有作为虎皮鱼低温胁迫分子标志物的潜能。     

军曹鱼MHC-Ⅰα基因全长cDNA的克隆及其组织表达分析

采用同源克隆和末端快速扩增（RACE）方法，得到1330bp的军曹鱼（Rachycentroncanadum）MHC-Ⅰα全长cDNA片段。该序列包括76bp的5’末端非编码区（UTR），189bp的3’UTR及1065bp的开放阅读框（ORF），编码354个氨基酸，预测其蛋白质分子量约40．10kDa，等电点5．70。构建MHC-Ⅰα氨基酸序列的系统进化树并进行氨基酸相似性比对，结果表明，军曹鱼和已知鱼类及人类（Homosapiens）MHC-Ⅰα氨基酸的同源性在27．9％～67．1％之间。所推测的蛋白序列具有一些重要特征，包括前导肽、α1、α2、α3区、CP／TM／CYT区和保守的半胱氨酸等。Real—timePCR检测结果显示，MHC-Ⅰα基因在各个正常军曹鱼组织中均表达，但表达量各有不同，其中较强的表达于头肾；中等程度表达于鳃、脾和肠；在心、脑和肌肉中表达较弱。     

鲈3种视黄醇类X受体基因cDNA的克隆和组织表达

视黄醇类X受体(retinoid X receptor,RXR)属于配体激活的核受体家族,在调节细胞内各种信号途径中起重要作用.采用RT-PCR和RACE技术,分离到鲈RXR基因3种亚型RXRα、RXRβ和RXRγ的cDNA序列.结果表明,得到的RXRα是长度为1 686 bp 3′末端不完整的cDNA序列,其中包括364 bp的5′非翻译区和1 322 bp的编码序列,可编码440个氨基酸.RXRβ cDNA全长为1 741 bp,其中包括150 bp的5′非翻译区,256 bp的3 ′非翻译区和1 335 bp的开放阅读框,共编码444个氨基酸,理论分子量为49.5 ku.RXRγ cDNA全长为1 847 bp,其中5′非翻译区为88 bp,3 ′非翻译区为397 bp,开放阅读框为1 362 bp,共编码453个氨基酸,分子量约为49.9 ku.氨基酸序列分析显示,鲈RXRα、RXRβ和RXRγ和其它物种的RXRs结构类似,在DNA结合区有P box和D box结构,配体结合区包括12个α螺旋和2个β折叠结构,H12的C端含有AF-2的激活区.系统进化树分析表明,鲈RXRα、RXRβ和RXRγ分别与其他动物的相应亚型聚类.组织分布特异性研究表明,鲈RXRα在肌肉、心脏、眼、大脑、肠、肾脏、脂肪、脾脏、鳃和肝脏10种组织中均有表达,但表达量较低；RXRβ在这10组织中都有较高表达,但心脏中表达量较低；在所检测的10种组织中,RXRγ都有表达,在肌肉、肠、肾脏、脂肪和脾脏表达量较高.     

奥利亚罗非鱼DMO cDNA的分离和克隆

采用RTPCR和RACE法分离和测定了奥利亚罗非鱼DMOcDNA的全序列。得到1571bp[不含poly(A)]的全长cDNA,包括148bp5’非翻译区,1230bp阅读框以及含Poly(A)信号AATAAA的193bp3’非翻译区[不包括Poly(A)]。阅读框共编码409氨基酸,与尼罗罗非鱼DMO编码的氨基酸序列进行比较,同源性为96.3%,表明DMO在同一物种中差别较小。而与尼罗罗非鱼,红鳍东方豚,虹鳟,青鱼将,鼠,人等动物的DMRT1编码的氨基酸序列进行比较,同源性分别为:25.7%,25.8%,24.3%,29.7%,22.5%,22.0%,这说明DMO和DMRT1可能是两个不同的基因。     

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.