3种光照条件下六面锥型罩式人工鱼礁模型对花尾胡椒鲷的诱集效果

为了解不同光照条件下人工鱼礁的集鱼效果，观察了自然光、55W和26W3种光照条件下在试验水槽内六面锥型罩式水泥人工鱼礁模型对花尾胡椒鲷（Plectorhynchus cinctu）的诱集效果。结果表明，在未投入礁体模型情况下，试验鱼出现的密集区位于水槽左端区域，试验鱼在此区域的平均出现率分别为61．60％（自然光）、81．61％（55W）和82．07％（26W），而试验鱼在空白礁区的出现率均低于5％；放人礁体模型后，鱼礁区试验鱼的出现率分别上升至37．60％（自然光）、23．56％（55W）和15．75％（26W），而原密集区试验鱼的平均出现率分别下降至23．47％（自然光）、71．61％（55W）和67．59％（26W）。统计数据显示，六面锥型罩式水泥人工鱼礁模型对花尾胡椒鲷具有显著的诱集作用，其诱集效果随着光照强度的降低而减弱。     

不同光色下人工鱼礁模型对褐菖鲉和日本黄姑鱼诱集效果试验

为研究不同光色下人工鱼礁的集鱼效果,在试验水槽中观察了人工鱼礁模型配置不同光色时褐菖鲉和日本黄姑鱼在水槽中的分布情况。结果表明,褐菖鲉在自然组的礁区聚集率高于有光组,不同光色对褐菖鲉的礁区聚集率有显著影响,礁区聚集率由小到大依次为橙光组<绿光组<红光组<蓝光组<白光组<自然组,褐菖鲉总体上表现出一定的负趋光性。所有试验组次中,日本黄姑鱼在礁区均无明显的聚集现象。配置不同光色的人工鱼礁模型对日本黄姑鱼的诱集效果与自然组无明显差异。     

3种人工鱼礁模型对黑棘鲷的诱集效果研究

为研究箱体礁(M1型)、三角形礁(M2型)、框架礁(M3型) 3种不同构造的人工鱼礁对黑棘鲷(Sparus macrocephlus)的诱集效果,通过室内模拟试验观察了不同人工鱼礁模型对黑棘鲷的活动和分布影响。结果表明:未放置人工鱼礁模型时,黑棘鲷随机分布于各试验区域;放置的3种人工鱼礁模型对黑棘鲷均具有一定的诱集效果,其中以有效空间最大、遮蔽效果最好的M1型人工鱼礁模型对黑棘鲷的诱集效果最佳; M2、M3型人工鱼礁模型对黑棘鲷的诱集效果随着礁体模型有效空间、遮蔽效果的减弱而逐渐降低,但数值分析结果表明,3种人工鱼礁模型对黑棘鲷的诱集效果之间不存在显著性差异(P 0. 05)。3种鱼礁对黑棘鲷的诱集效果差异可能由礁体模型的构造差异和黑棘鲷的习性共同决定。     

人工鱼礁和大型海藻对许氏平鲉和大泷六线鱼幼鱼的诱集作用

为了探究大型海藻和人工鱼礁对鱼类的诱集作用,依据崂山湾人工鱼礁区游泳动物和大型海藻调查结果,以海黍子、孔石莼、带形蜈蚣藻、石花菜和小珊瑚藻5种优势藻类,许氏平鲉和大泷六线鱼2种优势鱼类以及人工鱼礁模型为研究对象,于室内实验水槽观察了许氏平鲉和大泷六线鱼幼鱼在海藻和模型礁中的行为反应和分布。结果显示,水槽中未投放模型礁和海藻时,实验鱼密集出现在水槽边缘区(A9),分布率分别为75.71%±7.79%和73.63%±4.41%。放入模型礁和海藻丛后,许氏平鲉和大泷六线鱼出现短暂的排斥反应,然后迅速聚集其中;2种鱼对带形蜈蚣藻的响应时间最短[(12.75~21.00)s],对模型礁的响应时间最长[(66.50~151.25)s];带形蜈蚣藻聚集许氏平鲉用时最短[(151.50±8.14)s],海黍子聚集大泷六线鱼用时最短[(56.00±2.53)s];大泷六线鱼对模型礁的聚集时间为(216.25±5.59)s,远低于许氏平鲉(1343.50±5.38)s;2种鱼在模型礁中的停留时间远长于海藻丛,且大泷六线鱼的停留时间(211.85±7.96)s长于许氏平鲉(199.75±16.82)s。海藻丛和模型礁对2种岩礁性幼鱼的诱集效果明显,实验区幼鱼的分布率由未投放模型礁和海藻前的0.91%~8.78%上升到4.21%~31.42%;高密度带形蜈蚣藻和海黍子的诱集效果最好,对许氏平鲉和大泷六线鱼的聚集率分别达到30.42%±1.14%和31.42%±1.74%,而低密度小珊瑚藻的诱集作用不明显。     

三横山人工鱼礁区鱼类和大型无脊椎动物诱集效果初探

为了解人工鱼礁投放对鱼类和大型无脊椎动物(简称FM,以下同)的诱集效果,分别于2007年5、9月和2009年3、5、7月对上三横山人工鱼礁B区与泥底区进行了拖网本底和跟踪调查,并于2009年1-8月对下三横山人工鱼礁A区与鳗头山岩礁和泥底区进行了刺网调查。采用CPUE、Margalef种类丰富度d、经济种类数变化、Whilm多样性指数H′′等反映FM的资源状况。结果显示,(1)鱼礁A区和岩礁区在CPUE、种类丰富度、经济种和多样性上均无明显差异(P>0.05),而两者各指标与泥底区皆存在显著差异(P<0.05);(2)鱼礁B区,投礁后CPUE和经济种类数都明显高于投礁前也大于同期对照区,差异显著(P<0.05);礁区平均丰富度水平高出同期对照区31.1%(P<0.05);多样性水平相对投礁前和对照区都有一定提高,但尚无显著差异(0.05相似文献   

10种人工鱼礁模型对黑鲷幼鱼的诱集效果

为了解不同人工鱼礁的集鱼效果,在试验水槽内观察了深圳杨梅坑人工鱼礁区实际投放的10种礁体模型对黑鲷的诱集效果。结果表明,未投放礁体模型时,试验鱼在距离水槽中心40~70 cm的区域出现频次最高,且在试验水槽中分布较为分散。分别将10种礁体模型放入水槽后,对有礁及无礁时试验鱼随距离出现的频次进行曲线趋势回归显示,1-8号礁体模型试验中试验鱼出现频次最大的区域为距离水槽中心20~50 cm,而9号和10号礁为体试验鱼出现频次最大的区域则为距离水槽中心10~40 cm,分别比对照组试验鱼最大出现频次区域向中心点近移了20 cm和30 cm,说明10种礁体模型对试验鱼均有一定的诱集效果。对试验结果做模型礁诱集效率指数显示,模型礁体对试验鱼的诱集效果由强到弱分别为10号礁>9号礁>1号礁>2号礁>7号礁>4号礁>5号礁>6号礁>8号礁>3号礁。     

四种方形鱼礁对黑鲪和大陇六线鱼的集鱼效果

为了解不同构型的人工鱼礁对鱼苗的聚集效果,利用室内装置,在静水和流水条件下,研究了大窗箱型、大小窗箱型、"卍"字型和双层增殖型四种方形人工鱼礁及其不同组合对于大泷六线鱼(Hexagrammos otakii)和黒鲪(Sebastes schlegelii)的聚集行为的影响。实验结果表明,在静水条件下,大小窗箱型对黑鲪的诱集指数最高,为0.74,双层增殖型对大泷六线鱼的诱集指数达0.8;而在流水条件下,大小窗箱型和双层增殖型诱集指数均大于0.6。在实验的四种礁型中,上述两种礁型的诱鱼效果较好。     

黄鳍棘鲷幼鱼对不同开孔形状和直径的人工鱼礁模型的行为响应

为了分析岩礁性鱼类在不同开孔形状及不同开孔大小下的趋礁行为及空间分布, 以黄鳍棘鲷(Acanthopagrus latus)幼鱼为研究对象, 观察了不同开孔形状(菱形、圆形、正方形)、不同开孔大小(2.5、5、7.5、10 cm)人工鱼礁对鱼类的行为影响, 并通过行为分析软件 LoliTtrack Version 5 对黄鳍棘鲷幼鱼的平均速度、平均加速度、平均转弯速度、活动时间百分比以及平均分布坐标位置进行分析。结果表明, 在放入人工鱼礁后黄鳍棘鲷幼鱼在礁区的平均分布率有明显上升, 幼鱼在菱形开孔实验组人工鱼礁区的平均分布率最高, 为(27.32±4.93)%, 其次为正方形和圆形开孔实验组, 分别为(25.48±3.41)%和(19.83±5.59)%。另外开孔大小为 7.50 cm 的实验组中, 黄鳍棘鲷幼鱼在 VI 区的平均分布率最高, 为(29.18±4.75)%; 开孔大小为 2.50 cm 和 5.00 cm 的实验组中在 VI 区的平均分布率次之, 分别为(23.45±3.86)%及(23.04±5.51)%; 开孔大小为 10.00 cm 的实验组最低, 为(21.17±5.14)%。在运动能力方面, 黄鳍棘鲷幼鱼的平均速度、平均加速度和活动时间百分比在人工鱼礁模型实验组和空白对照组中均具有极显著性差异, 平均速度从空白对照组的(1.12±0.34) m/s 提高到(1.53±0.64) m/s; 平均加速度从对照组的(29.54±9.51) m/s²增加到(40.47±17.53) m/s²; 活动时间百分比从空白对照组的(77.13±12.66)%增加到(83.36±12.40)%。黄鳍棘鲷幼鱼的平均速度、平均加速度、平均转弯速度以及活动时间百分比在不同的礁体模型处理组之间均具有显著性差异。在开孔形状为菱形, 开孔大小为 7.5 cm 的礁体模型下, 平均速度、平均加速度以及活动时间百分比最低, 分别为 (0.81±0.31) m/s、(20.85±8.38) m/s² 和(67.44±17.45)%, 活跃程度最低, 而平均转弯速度最高, 为(56.79±22.80) deg/s; 在平均分布坐标位置方面没有显著性差异。研究表明, 加入人工鱼礁模型后, 黄鳍棘鲷幼鱼在开孔形状为菱形, 开孔大小为 7.50 cm 的礁体模型下, 黄鳍棘鲷幼鱼在模型区的平均分布率最大以及活跃程度最低, 该人工鱼礁礁体模型对黄鳍棘鲷幼鱼的诱集效果最好。本研究初步探究了黄鳍棘鲷幼鱼对不同类型鱼礁的趋礁行为变化, 研究结果可为针对特定物种的增殖型人工鱼礁的选型、设计等提供理论基础和参考。     

养马岛人工鱼礁区生物群落结构调查

2008年5月2213采用VideoRay ProIIIXE水下机器人对养马岛-17m深海域石块礁区和米字型构件礁区生物群落进行补充调查。礁区视频观测到游泳生物4种、底栖生物3种、附着生物3种及固着生物2种。刺参全部分布于石块礁区，半年石礁区小个体刺参生物量低，活动不明显，而2年石礁区内100g以上刺参密度达O．96ind]m3；大量许氏平鳓被诱集于米字型构件礁区中上部，密度高达4．89ind／m3。对半年石礁A区采样石块显微观测，发现附着生物多样性明显。对比本底区，人工鱼礁区增殖渔业生物资源显著，丰富生物多样性效果明显，且增殖效果与建礁时间正相关，礁体表面组建新的生物群落。建议该区增加箱型构件礁比例，投放大规格刺参苗种增殖，合理利用光照和温度梯度，建造以集鱼功能为主，增殖刺参、海藻功能为辅的大型堆投构件礁带，实现人工鱼礁渔业资源保护、增殖与休闲游钓等多种功能的有机结合。     

人工鱼礁竖板不同方形孔径对黑鲷幼鱼诱集效果研究

建设人工鱼礁是修复海洋生境、养护渔业资源的重要措施.钢筋混凝土鱼礁是常用的人工鱼礁类型,鱼礁竖板(侧板、内部间板)方形开孔是钢筋混凝土鱼礁结构设计中主要设计参数,竖板方形孔径大小是影响鱼类诱集效果的重要因素.以人工鱼礁区常见的礁栖鱼类黑鲷(Sparus macrocephalus)幼鱼为研究对象,设计制作具有不同方形孔...     

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.