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。     

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。     

美人蕉与背角无齿蚌对水质净化效果的研究

在总磷(TP)、总氮(TN)、叶绿素a(Chl a)分别为0.91、3.80、0.10 mg/L的水体中分别培养2.73 g/L美人蕉浮岛(A组)、8.77 g/L背角无齿蚌(B组)及2.66 g/L美人蕉浮岛+8.89 g/L背角无齿蚌(A+B组),并设置空白对照,以TP、TN、Chl a为监测指标,研究各实验组对水体水质的净化效果。结果表明,对TP的去除率依次为:A+B(83.27%)A(82.53%)B(71.51%)空白组(59.45%);对TN的去除率依次为:A+B(77.82%)A(72.77%)B(57.58%)空白组(31.68%);对Chl a的去除率依次为:A+B(99.53%)B(98.49%)A(96.16%)空白组(93.38%)。实验组对TP、TN、Chl a的去除率均显著(P0.05)高于空白组,美人蕉浮岛和背角无齿蚌搭配组对TP、TN、Chl a的去除效果最好,但对TP、TN的去除率均与单一移栽美人蕉的实验组间差异不显著(P0.05),而对Chl a的去除率与单一投加背角无齿蚌的实验组间差异不显著。实验结果表明,美人蕉对水体中氮磷的去除具有显著作用,背角无齿蚌对水体中藻类的去除具有显著作用,在富营养化水体的修复中美人蕉和背角无齿蚌的协同搭配能够加强水体中氮磷营养的循环,起到耦合强化净化能力的作用。     

南太湖入湖口叶绿素ａ时空变化及其与环境因子的关系

根据2010年1-12月专项监测数据,分析南太湖入湖口水域叶绿素a含量的时空变化特征以及与水温和营养盐等主要环境因子的相关性.研究表明,叶绿素a含量随时间变化明显,夏季最高,秋冬季次之,春季最低；在空间分布上,太湖西南入湖口水域的叶绿素a含量明显高于太湖南部入湖口水域.叶绿素a含量全年平均值为(15.71 ±11.24) μg/L,变化范围在1.50～74.3μg/L.叶绿素a含量与水温、pH、高锰酸盐指数(CODMn)、总磷(TP)、氨氮(NH4+-N)呈极显著正相关,与溶解氧(DO)、总氮(TN)、TN/TP呈极显著负相关.叶绿素a含量变化受多个因子共同影响,水温是叶绿素a含量变化的关键因子.氮磷比平均值为17.8,在藻类生长氮磷比的最佳范围内,易发生蓝藻水华.叶绿素a含量的对数与TP的对数呈极显著正相关,与TN和TN/TP的对数呈极显著负相关.磷是南太湖入湖口水域浮游植物生长的限制因子.     

白洋淀夏季叶绿素a与环境因子的相关性研究

采用回归统计方法分析白洋淀水产养殖区水质监测数据,研究白洋淀浅水草型湖泊夏季水体叶绿素a与环境因子的相关性,建立相应的回归方程。研究表明,白洋淀浅水草型湖泊水体叶绿素a含量与水温、pH、DO、COD、高锰酸盐指数呈显著正相关;叶绿素a与NH_4~+-N、NO_3~--N呈负相关,与NO_2~--N无明显相关,与TN无显著正相关;而叶绿素a与TP呈一定的正相关,白洋淀浅水草型湖泊可能是磷限制性湖泊。     

乌溪江水库富营养化程度及其影响因子时空分布探讨

为了解乌溪江水库主要水质指标的时空分布特征,探究其营养化程度的变化趋势,2019-2020年,对丽水市乌溪江水库的7个采样点（S1-S7）的水温、pH、总氮、总磷、叶绿素a等理化因子进行了监测。分析对比了综合营养指数和理化因子等关键指标在不同时期的分布特征。结果表明,乌溪江水库的营养盐浓度呈现出春夏高秋冬低、从上游（S1）至下游（S7）逐渐下降的趋势,平均综合营养指数也从47.1（S1）下降到32.5（S7）,整体上属于中营养化水库。总磷浓度在0.002-0.040mg/L间,平均值为0.012mg/L;总氮浓度在0.412-2.826mg/L间,氮的主要赋存形式为硝酸盐。叶绿素a含量均值为3.77 ug/L,河流区的叶绿素a含量显著高于下游的过渡区和湖泊区。分析表明：汛期地表径流带来的富营养化压力最大,同时也是氮磷等外源性营养盐输入水体的主要途径;WD、pH、TP和叶绿素a含量中等程度相关,水库生态系统具备很强的净化能力。但近年来富营养化程度加剧。     

洞庭湖氮磷时空分布及形态组成特征

为探究洞庭湖水体营养盐形态结构与时空分布特征,分别于2014年8月(丰水期)和2015年1月(枯水期)在入湖河流、湖体、出湖口设置16个代表性断面采集水样,分析了氮、磷营养盐的特征指标。结果表明:1洞庭湖水体中,总氮(TN)含量为1.60~3.65 mg/L,平均值2.25 mg/L,总磷(TP)含量为0.060~0.359 mg/L,平均值0.138 mg/L;颗粒态总氮(TPN)含量为0.07~1.39 mg/L,平均值0.25 mg/L,颗粒态总磷(TPP)含量为0.003~0.172 mg/L,平均值0.05 mg/L;2时空分布上,水体中氮、磷含量整体表现为丰水期高于枯水期,出湖口最高,东洞庭湖高于西、南洞庭湖,入湖河流差异大的特征,颗粒态氮磷呈现自西向东呈逐渐增加趋势,与悬浮物(SS)的空间分布一致;3形态组成上,洞庭湖水体中氮磷以溶解态为主(TDN/TN为88.0%、TDP/TP为66.7%),三峡工程2003年蓄水前后,洞庭湖磷营养盐形态组成发生了大的变化,由以颗粒态磷为主(TDP/TP 20.0%~35.6%)转变为以溶解态为主,而氮营养盐形态组成基本未变;4营养结构上,洞庭湖大多数断面TN/TP在10~22,且氮、磷浓度远高于水体富营养的限制阈值,比较适宜藻类生长。相关分析显示,洞庭湖TN、TP、TDN、TDP均与Chl-a相关性不显著,因此认为洞庭湖氮、磷营养盐对藻类生长的限制作用不明显。     

云南高原湖库浮游细菌的生态分布及其影响因素

2009年秋季,对我国西南云贵高原8个处于不同营养水平的湖泊和水库的浮游细菌进行了调查,分析了浮游细菌的分布特征及其与温度、总氮(TN)、总磷(TP)、正磷酸盐(PO4-P)、氨氮(NH4-N)、硝氮(NO3-N)、化学需氧量(CODMn)和叶绿素a(Chl.a)的相关性。结果表明,8个湖库的浮游细菌数量存在明显差异,异龙湖最高,平均值为5.66×109个/L,阳宗海最低,平均值为2.25×109个/L,从大到小依次为:异龙湖>草甸海>松花坝水库>白沙河水库>月湖>松茂水库>石龙坝>阳宗海。对阳宗海4个点位的研究发现,同一湖泊内浮游细菌的数量存在空间异质性,沿岸带明显大于湖心区。浮游细菌数量与水温、总氮、总磷、叶绿素a均呈极显著性相关(P<0.01),表明上述因子可能是浮游细菌分布的主要限制因子。     

阳澄西湖及其入湖港口的水质评价与分析

为了探明阳澄西湖湖区及其入湖港口的水质现状,为其后续水环境治理提供参考,选取湖区6个位点和4个港口,于2016年5月至2017年3月监测其水质,逢单月月初采样;监测的水质参数包括水深(H)、酸碱度(pH)、溶解氧(DO)、透明度(SD)、悬浮物(TSS)、总氮(TN)、氨氮(NH~+_4-N)、亚硝酸盐氮(NO~-_2-N)、总磷(TP)、活性磷酸盐(PO■-P)、叶绿素a (Chl-a)、高锰酸盐指数(COD_(Mn))、总有机碳(TOC)。运用主成分分析法探讨了水体主要污染因子,采用皮尔逊相关性分析法探究湖区TN、TP对Chl-a浓度的影响。结果显示,阳澄西湖水质综合营养状态指数年均值为57.9,主要水质参数的时空分布表现为枯水期(5-7月)优于丰水期(11-1月),湖区优于入湖港口,北部优于南部。湖区TN和TP年均值为2.63 mg/L和0.217 mg/L,Chl-a年均值为21.74μg/L,且以9月最低。主成分分析显示,NH~+_4-N、NO~-_2-N、PO■-P、TP、TN是湖区水质主要的污染因子,TP、NH~+_4-N、NO~-_2-N、TN是港口水质的主要污染因子。皮尔逊相关性分析显示,阳澄西湖的Chl-a浓度与TN呈正相关(P0.01),与TP的相关性不显著(P0.05),且相关系数为负值。研究表明,阳澄西湖的Chl-a对营养物质的响应不灵敏,后续治理中需加强对外源氮磷的拦截。     

诸暨养殖池塘内水环境、三角帆蚌生长与珍珠产量

2006.06.03-11.08研究了浙江省诸暨市3口蚌养殖池塘内的水温、透明度(SD)、溶氧(DO)、pH等理化因子以及三角帆蚌(Hyriopsis cumingii)生长和珍珠产量。结果显示:实验期间池塘内水温平均为28℃,透明度为24~31 cm,pH为8.5~8.8,DO为6.6~7.8 mg/L,盐度为0.1,Ca2+含量为19.4~37.0 mg/L,总硬度为64.0~123.3 mg CaCO3/L,总碱度为58.4~109.4 mg CaCO3/L,TN为0.76~1.12 mg/L,TP为0.14~0.33 mg/L,TN/TP为4~8,CODMn为9.99~15.5 mg/L。经过158 d生长,池塘内育无核珠或有核珠的3龄蚌蚌壳长增加0.16~0.94 cm,蚌重增加21~61 g;育无核珠的5龄蚌蚌壳长增加0.1~0.25 cm,蚌重增加27~76 g。蚌壳和蚌重生长速度受蚌龄影响,蚌重生长速度的变化幅度往往比蚌壳大。育无核珠的3龄蚌和5龄蚌内珍珠增重分别为每蚌2.03~2.87 g和3.52~5.23 g。3龄蚌蚌壳长和蚌重生长比5龄蚌快,但珍珠产量低于后者,表明三角帆蚌珍珠产量与其蚌壳和蚌重生长速度并不完全一致。     

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.