藻蚌混养对养殖尾水的作用效果研究

为了研究小球藻(Chlorella vulgaris)和三角帆蚌(Hyriopsis cumingii)混养模式净化养殖尾水水体的效果，本实验共设计4个处理组，藻蚌组、蚌组、藻组、空白对照，每组处理重复三次，取鱼类养殖尾水净化。结果显示：藻蚌组、蚌组和藻组对总氮(TN)去除率分别为90.03%、91.96%和89.58%;对总磷(TP)去除率分别为50.89%、26.36%和45.79%,对氨氮(NH⁺₄-N)去除率分别为53.77%、34.96%和42.64%;化学需氧量(COD)去除率分别为74.84%、57.75%和80.56%。实验结果表明，单用小球藻和单用蚌对尾水处理都有一定的效果，但是都有局限性。单用小球藻前期对TN、TP和NH⁺₄-N去除效果较好，但是随着天数增加，TN、TP和NH⁺₄-N浓度也随之增加，小球藻的生长受到了抑制，去除效果变差。单用蚌不论是TN、TP还是NH⁺₄-N和COD,都比藻蚌组...     

河蚌和水培植物组合协同净化水体的效果研究

本试验研究底栖动物背角无齿蚌(Anodonta woodiana)与水培植物白掌(Spathiphyllum kochii)和降糖草(Gynura divaricata DC)协同净化水质效果,为室外生态浮床技术奠定基础。室内进行动植物组合处理供试水样,测定TN、TP、叶绿素a的去除率和水体浊度。处理组对TN去除率依次为降糖草白掌河蚌降糖草组合河蚌白掌组合,无显著差异(P0.05);降糖草对水体中TP去除率最高为63%,与其它处理组有显著差异(P0.01);有河蚌的处理组容易使水体的浊度上升。综合考虑降糖草和河蚌降糖草组合更适合在室外富营养化水体中生长,兼具生态和景观美化效果,可为水产养殖水体及景观水体进行生态修复提供参考。     

蛋白核小球藻与水蕹菜调控对南美白对虾养殖水体及其生长影响的初步研究

为了解接种蛋白核小球藻(Chlorella vulgaris)和种植水蕹菜(Ipomoea Aquatica)对南美白对虾(Penaeus vannamei)养殖的影响,在南美白对虾养殖水体中设置空白对照组、单纯接种蛋白核小球藻、种植水蕹菜及二者联合的4个处理组,定期监测各处理组中水质理化指标、生长特性及免疫相关酶活性的变化情况。结果显示:与对照组相比,三个处理组均能有效去除南美白对虾养殖水体中的NO~-_2-N、NH~+_4-N、TN和TP,其中接种蛋白核小球藻处理组对NO~-_2-N的去除率达到51.27%;种植水蕹菜处理组对NO~-_2-N、NH~+_4-N和TP去除效果最好,去除率分别为55.19%、70.06%和74.76%;联合处理组对水体TN去除率为49.66%,去除TN效果最佳。三个处理组均能提高南美白对虾的特定生长率和提高其成活率,其中联合处理组效果最佳,分别较对照组提高了0.66%和27.27%,水雍菜处理组分别增加了8.14%和9.10%,蛋白核小球藻处理组分别增加了4.41%和2.28%,同时联合处理组的增重率显著高于其他三组。种植水蕹菜处理组能显著增加南美白对虾CAT、GST活性和GSH含量,分别较对照组增加了128.84%、235.39%和426.26%;联合处理组对南美白对虾肝胰腺的SOD活性和GSH含量促进效果最佳且达到显著水平,分别较对照组增加了52.75%和1 376.69%。综上可见,接种蛋白核小球藻和种植水蕹菜均能不同程度地促进南美白对虾生长及免疫活性,且以联合处理的综合效果最佳。     

密度和收割对水蕹菜净水效果的影响

通过在水桶试验中设置2种不同处理方式(密度和收割),研究水蕹菜(Ipomoea aquatic Forsk)对富营养水质的净化特性及效果。结果表明:室外培养12 d,高密度组(10 g/L)对NO2-、NO3-、PO32-、TN、TP和Chl-a的平均去除率最高,分别为90.88%、93.98%、98.96%、82.36%、88.89%和89.33%,显著高于对照组(0 g/L);收割有助于刺激植物加速分蘖、促进植物对N、P元素的吸收固定,并改善水体的DO;水蕹菜组织N、P含量在试验前后发生变化,并与生长水体中的N、P浓度呈正相关关系;植物固定对水体中N、P去除的贡献率与植菜密度呈正相关关系,占高密度组水体中TN、TP去除总量的52.05%和40.41%,为试验组水体中N、P去除的主要途径。     

2种淡水蚌类对水环境中Cu、Zn和Cd的去除与累积

2007年10月,在室内模拟条件下初步研究了成年背角无齿蚌和三角帆蚌对水环境中的Cu、zn和cd的去除与累积.随着暴露时间的延长,2种淡水蚌在不同重金属浓度处理下.对水体中Cu、Zn、Cd的去除率均呈下降趋势.相同重金属浓度处理下,背角无齿蚌对水体中Cu、Zn、Cd的去除率分别为三角帆蚌的1.2、1.9、1.5倍.统计分析结果表明,淡水蚌种类、重金属浓度、蚌不同组织对其体内Cu、Zn、cd含量的影响均存在显著效应(P<0.05).2种淡水蚌各组织对Cu、Zn、Cd的富集系数平均值均随处理中重金属浓度的增加而下降,且不同浓度处理下淡水蚌鳃对Cu、Zn,Cd的富集系数平均值远高于足、外套、壳.     

不同地区三角帆蚌养殖水体理化环境的季节变化

分别于2006年9月、2006年12月、2007年3月和2007年7月调查了分布在江苏省苏州市、浙江省杭州市和绍兴市、湖北省荆州市、江西省九江市的10个三角帆蚌(Hyriopsis cumingii)养殖水体的理化环境。结果表明调查期间上述水体水温为6.5~34.0℃,Ca2+为17.89~66.54 mg/L,总硬度为61.02~217.78 mg CaCO3/L,总碱度为43.30~218.24 mg CaCO3/L,总氮(TN)为0.46~2.78 mg/L,总磷(TP)为0.01~0.35 mg/L,高锰酸盐指数(COD Mn)为4.36~17.98 mg/L。从地点上看:苏州、杭州、绍兴的水体水温和透明度高于九江和荆州的水体,但表层溶氧(DO)、pH和总碱度低于后者;苏州的水体盐度、Ca2+和总硬度高于九江、荆州、杭州和绍兴的水体;杭州、绍兴的水体TN和TP高于九江、荆州和苏州的水体;荆州的水体COD Mn高于杭州、绍兴、九江和苏州的水体。从时间上看:7月和9月水温、TP和COD Mn高于3月和12月,而表层DO、pH、Ca2+、总硬度和TN低于后者;透明度、盐度和总碱度季节变化趋势不明显。所调查的水体DO、COD Mn与水温相关,TN、TP与DO相关,表明DO、COD Mn、TN、TP随水温变化而变化。     

罗氏沼虾不同养殖模式对水体浮游生物的影响

通过围隔实验比较罗氏沼虾不同养殖模式对水体浮游生物的影响。实验设置6种养殖模式:罗氏沼虾单养(MP)、罗氏沼虾+浮萍(水面覆盖率5%)(PP)、罗氏沼虾+鲢(PF)、罗氏沼虾+背角无齿蚌+鲢(PMF)、罗氏沼虾+背角无齿蚌+浮萍(PMP)、罗氏沼虾+背角无齿蚌+浮萍+鲢(PMPF)。养殖64 d后,测定不同模式中浮游植物和三大类浮游动物(轮虫、枝角类及桡足类)的种类和数量。结果显示,上述6种模式中浮游植物共同优势种有4种,但优势度指数最大的浮游植物不同,MP组是锥囊藻属,有浮萍的PP和PMP组均为细小平裂藻,混养鲢的PF、PMF和PMPF组均为针杆藻。不同养殖模式无共同的浮游动物优势种。养殖模式对浮游生物密度具有显著影响,PF组浮游植物密度最高,MP组浮游植物密度最低,PF组浮游植物密度比MP、PP和PMP组分别高78%、53%和61%。相反,浮游动物密度MP组最高,PF组最低。混养鲢的PF、PMF和PMPF组浮游动物密度显著低于其他3组。研究表明,罗氏沼虾养殖中混养鲢可增加浮游植物密度而降低浮游动物密度,浮萍和鲢影响池塘优势种。     

南太湖近岸水域叶绿素a含量与氮磷浓度的关系

2007年6月-2008年4月对南太湖近岸水域进行了4次生态环境调查,在此基础上,对叶绿素a含量(Chl.a)与总氮(TN)、总磷(TP)浓度及氮磷比(N/P)的关系进行了统计分析。结果表明:南太湖水体中Chl.a含量与TN浓度的关系存在显著的季节差异,在蓝藻水华大范围爆发的2007年6月和2008年4月2者呈极显著的正相关,而2007年10月和2008年1月2者无显著性关系;Chl.a含量与TP浓度在4次调查中皆无显著相关关系;岭回归分析显示,N/P 10～25是南太湖水体中附着藻类的最佳生长范围,此时总氮、总磷浓度及氮磷比与Chl.a含量呈显著的正相关,4者的多元回归关系为Chl.a=-0.0012+0.0064 TN+0.0215 TP+0.0005N/P(R=0.543,P<0.023)。总体来说,南太湖水体中的总氮、总磷浓度及氮磷比皆在藻类生长的适宜范围内,氮磷浓度处于较高水平,已经不是藻类生长的限制因素,在不同水温、光照等环境因子的作用下,加上本水域复杂的水文和季风共同影响下形成了蓝藻水华爆发的季节性差异。     

印度小竹节草的生物修复潜力研究

为探究印度小竹节草的生物修复潜力，本研究采用实验生态学方法研究了印度小竹节草对铜绿微囊藻的抑制作用和富营养化水体氮磷的去除效果。实验通过分别设置4个栽培密度（1，2，3和4 g/L），3个营养盐梯度（中营养，富营养和极富营养），跟踪检测了培养液中硝氮（NO3-N）、亚硝氮（NO2-N）、氨氮（NH4-N）、总氮（TN）和总磷（TP）的浓度变化；并对印度小竹节草与铜绿微囊藻共培养下铜绿微囊藻的生长状况及营养盐的衰减状况进行了初步研究。结果表明，印度小竹节草具有很强的营养盐去除能力，栽培密度为4 g/L时，TN和TP去除率最高，分别为99.50%和93.45%，各处理组间的TN和TP去除率差异性不显著。营养程度对印度小竹节草N、P吸收速率具有极显著性影响，N、P吸收速率随着各组 N、P 浓度的升高而增加，极富营养处理组TN、TP吸收速率达到最高，分别为1.11和0.15 μmol/(g ? h)。同时，极富营养处理组TN、TP去除率也显著高于其他处理组，分别高达99.46%和90.75%。共培养实验表明，印度小竹节草对铜绿微囊藻具有较好的抑制效果，抑藻率高达99.89%。实验组TP浓度后期大幅度下降，与对照组存在极显著差异性，且NH4-N浓度极显著低于对照组。综合以上实验结果，印度小竹节草可考虑作为生物修复物种在富营养化水体进行种植，同时在铜绿微囊藻水华预防方面也具有一定的应用潜力。     

光合细菌和枯草芽孢杆菌对养殖水质的净化作用

以光合细菌(Photosynthetic bacteria,P)和枯草芽孢杆菌(Bacillus subtilis,B)为实验菌种,研究两者最佳浓度配比的复合菌组对淡水养殖水质的净化作用。试验设置1个对照组(CK)和5个复合菌组(PB1、PB2、PB3、PB4、PB5),5个复合菌组浓度配比分别为(2.0×105+1.5×105)CFU/m L、(2.0×105+3.0×105)CFU/m L、(2.0×105+4.5×105)CFU/m L、(4.0×105+1.5×105)CFU/m L、(6.0×105+1.5×105)CFU/m L,分析各试验组的化学需氧量(COD)、氨氮(NH3-N)、溶解氧(DO)、p H等水质指标。结果显示:复合菌能够明显去除水体CODMn,PB2组去除率最高达,44.98%;能有效增加DO,PB2组增氧率最高,为27.9%;能明显去除氨氮,PB2组去除率最高达78%;并且能稳定p H值在8.6左右,5个复合菌组差异不显著(P0.01)。复合菌发挥最佳净化能力的时间约在6~8 d。结果表明,复合菌最佳浓度配比为(2.0×105+3.0×105)CFU/m L,该浓度组较对照组和其他试验组能够显著净化淡水养殖水质,有效改善养殖环境。     

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.