长江、珠江、黑龙江三水系的鲢、镛、草鱼原种种群的生化遗传结构与变异

用LKB平板电泳仪聚丙烯酰胺凝胶电泳测定了长江、珠江及黑龙江的鲢、鳙及草鱼的原种8个种群16个酶位点的遗传变异。同种鱼不同水系种群之间存在着明显的生化遗传差异。长江、珠江、黑龙江鲢鱼种群的多态位点的比例分别是13.3％、26.7％、13.3％,平均杂合度分别是0.0493、0.0484、0.0511;长江、珠江鳙鱼种群的多态位点的比例都是31.3％,平均杂合度分别是0.1375,0.0977;长江、珠江、黑龙江草鱼种群的多态位点比例分别是30％,38％,23.1％,平均杂合度分别是0.1241,0.0961,0.0525。南方种群的多态位点比例有比北方的高的趋向。长江鲢—珠江鲢,长江鲢—黑龙江鲢,珠江鲢—黑龙江鲢的遗传相似度依次是0.9957,0.9955及0.9696;长江鳙—珠江鳙的遗传相似度是0.9955;长江草鱼—珠江草鱼,珠江草鱼—黑龙江草鱼,长江草鱼—黑龙江草鱼的遗传相似度依次是0.9679、0.9483及0.9324。长江种群与珠江种群这两个中央群体间的遗传差异较小,边缘群体黑龙江种群与中央群体长江、珠江种群间的遗传差异较大。黑龙江草鱼种群很小,其资源的保护工作应引起注意。     

合浦珠母贝2个野生种群的遗传多样性

用形态特征比较与同工酶电泳分析相结合的方法，对产于我国部湾和大亚湾的野生合浦珠母贝（pinctada martensii)的遗传多样性进行研究，结果表明，在贝壳形态方面，北部湾种群的平均壳长与壳高都略大于大亚湾种群，壳高与壳长呈乘幂相关，壳宽与壳长呈对数相关，大亚湾种群的壳宽指数，壳重指数和肥满度指标都大于北部湾种群，用聚丙烯酰胺梯度凝胶电泳检测由26个位点编码的12种同工酶，2种群都显示出较高的多态性，北部湾种群多态位点的比率为38．46％，大亚湾种群则为46．15％，都表现出明显的杂合子缺失现象，北部湾种群的平均杂合度（0．0999）小于大亚湾种群（0．1243），2种群之间的遗传距离为0．0159,本文还讨论了引种2种群杂合子缺失现象的原因，并认为生化遗传分析的结果与2个种群的形态特征是相关联的。     

黄海和日本海黄鮟鱇的形态和同工酶差异

对中国黄海及日本新泻县粟岛近海的黄鮟鱇形态进行了比较研究,并采用水平淀粉凝胶电泳技术分别分析了黄海和日本海黄鮟鱇的遗传结构及其遗传多样性。结果表明,黄海和日本海黄鮟鱇群体计数性状中除第2背鳍鳍条数平均值表现出一定的差异,其余性状没有明显差异;二者在体长/臀鳍基长、头长/眼径指标未表现出显著差异,其余可量性状比上表现出了显著差异。同工酶分析表明,中国黄海黄鮟鱇群体共记录了8个基因位点,其中,LDH*、AAT*、GPI*和G3PDH*共4个基因位点呈多态,其多态座位比例为0.5,平均观测杂合度和预期杂合度分别为0.027和0.026,平均有效等位基因数为1.028,遗传偏离指数均大于零;而检测的日本海群体的6个基因位点中,没有出现多态位点。黄海和日本海黄群体间的遗传距离为0.00046,二者的遗传多样性水平较低,群体间没有明显的遗传分化。     

不同罗氏沼虾种群形态差异的比较研究

采用3种多元分析方法，对8个罗氏沼虾（Macrobrachium rosenbergii）种群（浙江养殖种群，缅甸引进种群及6个不同组合杂交种群）的12个形态比例参数进行比较研究。聚类分析和主成分分析法对雌、雄虾的分析结果表明，6个杂交种群的形态较为接近，而与养殖种群和引进种群的趋异程度逐渐增加。构建的5个雌体主成分中，方差贡献率分别为主成分（1）26．191％、主成分（2）16．036％、主成分（3）13．309％、主成分（4）10．769％、主成分（5）10．166％，累积贡献率为76．471％。相应地，雄体的方差贡献率分别为主成分（1）25．206％、主成分（2）20．277％、主成分（3）16．985％、主成分（4）13．222％、主成分（5）8．945％，累积贡献率为84．634％。判别分析结果显示，8种群之间的形态参数之间有极显著的差异（P〈0．01）；8种群雌体判别函数的判别准确率P1为60．03％～100．00％，P2为33．30％～100％，综合判别率为92．1％；雄体判别准确率P1为20．00％～100．00％，P2为20．00％～100％，综合判别率为86．4％。其中判别函数对养殖种群，缅甸引进种群和“反交正回交”3个种群的判别准确率较高。综上所述，养殖种群和引进种群在形态上已经出现了明显的分化，并独立成为2个不同的种群；其他杂交种群由于同时综合了养殖种群和引进种群两者的相关性状，形态上没有呈现显著的差异（P〉0．05）。[中国水产科学，2006，13（4）：530-535]     

团头鲂三倍体的微卫星遗传特征及生长性能分析

为研究团头鲂三倍体育种,对团头鲂三倍体和二倍体2个群体进行微卫星遗传结构特征分析和生长性能比较.利用筛选得到的20个微卫星标记对团头鲂三倍体和二倍体进行遗传多样性分析.试验结果表明,团头鲂三倍体、二倍体的平均等位基因数分别为2.75、3.05,平均期望杂合度分别为0.5061、0.5412,平均多态信息含量分别为0.4...     

长江、珠江、黑龙江三水系的鲢、鳙、草鱼原种种群的生化遗传结构与变异

用LKB平板电泳仪聚丙烯酰胺凝胶电泳测定了长江、珠江及黑龙江的鲢、鳙及草鱼的原种8个种群16个酶位点的遗传变异。同种鱼不同水系种群之间存在着明显的生化遗传差异．长江、珠江、黑龙江鲢鱼种群的多态位点的比例分别是13．3％、26．7％、13．3％，平均杂合度分别是0．0493、0．0484、0．0511；长江、珠江鳙鱼种群的多态位点的比例都是31．3％，平均杂合度分别是0．1375，0．0977；长江、珠江、黑龙江草鱼种群的多态位点比例分别是30％，38％，23．1％，平均杂合度分别是0．1241，0．0961，0．0525。南方种群的多态位点比例有比北方的高的趋向。长江鲢-珠江鲢，长江鲢-黑龙江鲢，珠江鲢-黑龙江鲢的遗传相似度依次是0．9957，0．9955及0．9696；长江鳙-珠江鳙的遗传相似度是0．9955；长江草鱼-珠江草鱼，珠江草鱼-黑龙江草鱼，长江草鱼-黑龙江草鱼的遗传相似度依次是0．9679、0．9483及0．9324。长江种群与珠江种群这两个中央群体间的遗传差异较小，边缘群体黑龙江种群与中央群体长江、珠江种群间的遗传差异较大。黑龙江草鱼种群很小，其资源的保护工作应引起注意。     

罗氏沼虾缅甸野生群体和浙江养殖群体的遗传多样性比较

采用形态学方法、同工酶电泳技术和DNA分析方法对罗氏沼虾(Macrobrachium rosenbergii DeMan)缅甸野生群体(BNP种群)和浙江省养殖群体(ZCP种群)的遗传多样性进行比较分析。结果表明,两种群在外形、体色、生长等方面存在一定的差异;对罗氏沼虾11种酶的25个基因位点进行分析,得出BNP种群和ZCP种群的同工酶分析所得出的多态位点比例及平均杂合度分别为12％和:16％,0.0431和0.0501。根据同工酶的基因频率计算得两种群的遗传相似系数为0.9963,遗传距离为0.0037;22个经筛选的10bp随机引物共检测到139个RAPD位点,BNP种群的多态位点比例和遗传多态度(Ho)分别为33.81％和0.0940,高于ZCP种群的30.22％和0.0780,两个群体的平均遗传多态度(Hpop)为0.0860,90％以上的遗传变异是在群体内检测到的。根据RAPD扩增的基因频率得出两群体间的遗传距离为0.1206。无论是同工酶电泳结果还是RAPD分析结果,都表明罗氏沼虾缅甸野生群体的遗传多样性高于浙江养殖群体,说明人工养殖会导致罗氏沼虾遗传多样性的下降。结果还表明,罗氏沼虾群体遗传多样性水平欠丰富,因此需要对罗氏沼虾群体实行科学的管理。     

鲇细胞色素b基因序列差异及遗传多样性分析

从4个种群的鲇(Silurus asotus)线粒体DNA(mitochondrial DNA,mtDNA)扩增出约500 bp的细胞色素b基因,经Clustal X同源排序后得400 bp序列.用PopGen32软件计算遗传距离和遗传一致度.17个个体间的遗传距离的变化范围为O～0.0211,遗传一致度的变化范围为1-0.9791.结果显示,在长江上游的支流中,雅砻江种群在该基因片段上基本不存在变异,在被分析的4个个体中,其细胞色素b基因的序列完全一致;岷江种群和乌江种群在该基因片段上有一定的变异.沅江上游的海阳河种群在该基因片段上基本不存在变异,在被分析的5个个体中,其细胞色素b基因的序列完全一致.但各个种群问在该基凶片段上差异较大.在4个种群的鲇Cytb基因比较分析的基础上,构建了遗传关系聚类图,雅砻江、岷江、乌江、潕阳河4个种群各聚为一支后,雅砻江和岷江2个种群再聚为一支,乌江和潕阳河2个种群再聚为另一支.     

贵州3个斑鳜野生种群形态学差异

为探究贵州境内沅江、柳江和乌江水系野生斑鳜外形差异,基于形态学和框架结构测量数据,运用多元分析法比较3条水系斑鳜种群的形态特征,经数据标准化和参数选择后12项比例性状和12项可数性状进行统计分析。研究结果显示,单因素分析中9项可数性状之间差异显著(P<0.05);主成分中提取了前6个主成分,其累计贡献率为72.668%,前3项主成分对种群间外形差异贡献较大,主要受其尾柄长、眼间距和体宽等性状影响。应用逐步判别方法建立了这3个种群的特征判别函数,其交互验证判别准确率为81.5%。形态学聚类图结果显示,沅江和柳江种群形态关系较近先聚为一支,之后再与乌江种群相聚。差异系数分析表明,乌江种群与沅江和柳江种群在尾柄长/体长性状上的差异达到亚种水平(差异性系数>1.28)。综上可知,贵州3个斑鳜种群在形态学上存在一定差异,其中柳江与沅江形态差异较小,乌江与其差异较大,建立的判别方程可对3个种群进行区分。本研究结果可用于3个水系斑鳜种群的识别,也可为种群保护和育种利用提供理论依据。     

野生坛紫菜种群遗传多样性的ISSR分析

采用简单序列重复区间(ISSR)分子标记技术对福建省的3个野生坛紫菜(Porphyrahaitanensis)种群共60个个体进行了遗传多样性分析.15条引物共扩增出222个位点,其中186个位点具有多态性,多态位点百分率为83.78%,在种群水平上,多态位点百分率为80.18%～81.53%,平均为80.93%.期望杂合度、Shannon信息指数在物种水平上分别为0.3304和0.4834;在种群水平上分别为0.3089和0.4551,表明坛紫菜种群内存在着较高的遗传多样性水平,且在三个种群间没有明显差异.依据Gst值,坛紫菜的遗传变异主要发生在种群内的个体间(占93.5%),只有6.5%的遗传变异发生在种群间,由此说明坛紫菜种群间的遗传分化水平很低,这与坛紫菜种群间充分的基因交流(Nm=7.1930)是相关的.基于遗传距离的UPGMA聚类结果表明坛紫菜60个个体并不按照其地理分布进行分群,而是随机分群的.文章最后还对坛紫菜种质资源保护的必要性进行了讨论.     

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.