南海北部海域中国枪乌贼角质颚的形态学分析

角质颚是头足类的重要硬组织,已成为头足类渔业生物学及海洋生态学等重要研究材料之一。此研究利用2015年在南海北部海域采集的102尾中国枪乌贼(Uroteuthis chinensis)样本,测定其个体以及角质颚形态学参数,使用主成分分析法获得其角质颚主要形态特征参数,分析角质颚特征参数与胴长(ML)、性成熟等的关系,建立主要形态参数与胴长和体质量(BW)的关系模型。主成分分析表明,上头盖长(UHL)、上脊突长(UCL)、上侧壁长(ULWL)、下侧壁长(LLWL)、上喙宽(URW)、下喙长(LRL)可代表中国枪乌贼角质颚的形态特征。UHL、UCL、ULWL、LLWL与胴长之间以指数模型为最佳,URW、LRL与胴长之间以线性模型为最佳。UHL、UCL、ULWL、LLWL与体质量之间以线性模型为最适,URW与体质量之间以幂函数模型为最适,LRL与体质量之间以对数模型为最适。性成熟及生长对角质颚形态参数特征UHL/UCL影响无统计学意义(P0.05)。     

2种大洋性柔鱼类角质颚形态识别法的比较

依据中国鱿钓船2013年8~10月在北太平洋海域采集的柔鱼(Ommastrephes bartramii)和2014年4~7月在中东太平洋海域采集的茎柔鱼(Dosidicus gigas)样本,分别运用传统测量学法和傅里叶分析法对2种柔鱼类的角质颚进行识别,并对结果进行比较分析。运用传统测量学法共选取了12项角质颚参数值比较形态差异;角质颚外部轮廓形态通过软件转化为20组傅里叶代码(EFDs)后选取77个傅里叶值进行判别分析。结果表明,2种柔鱼类上、下角质颚形态在上头盖长(UHL)、上脊突长(UCL)、上喙长(URL)、上喙宽(URW)、上侧壁长(ULWL)、下脊突长(LCL)、下喙长(LRL)、下喙宽(LRW)、下侧壁长(LLWL)、下翼长(LWL)中存在显著性差异(P0.01),上翼长(UWL)、下头盖长(LHL)不存在显著性差异(P0.05)。主成分分析结果显示,传统测量法中下喙长(LRL)和下喙宽(LRW)与胴长(ML)之比主成分得分最高;傅里叶分析法显示上角质颚前16主成分可以解释总变异的83.58%;下角质颚前16主成分可以解释变异的73.76%。逐步判别分析将上头盖长(UHL)、上喙长(URL)、上侧壁长(ULWL)、下头盖长(LHL)、上喙长(URL)、上喙宽(URW)与胴长(ML)之比纳入判别分析函数,总别正确率为95%;傅里叶分析法将18个傅里叶值纳入判别函数,上颚总判别率为97.6%;下颚总判别率为85.7%。总体而言,2种方法对柔鱼类角质颚判别均有效,且上颚区分效果更明显。本文为头足类的种类判别提供了更多的且有效的识别方法。     

秘鲁外海茎柔鱼角质颚的形态特征及其与个体大小和日龄的关系

角质颚是头足类重要的硬组织,被用于估算其个体大小及其生物量等。根据2009~2014年中国鱿钓船在秘鲁外海(79°22'W~84°30'W、10°00'S~18°16'S)采集的茎柔鱼(Dosidicus gigas)样本,提取出1 346ind茎柔鱼的角质颚,并对角质颚的形态进行了分析,建立了角质颚的形态特征参数与胴长、体重和日龄之间的关系。结果显示,雌性个体角质颚各形态参数的平均值均大于雄性个体,在角质颚12个形态参数中,上喙长(UHL)、上脊突长(UCL)、上侧壁长(ULWL)、下脊突长(LCL)、下侧壁长(LLWL)、下翼长(LWL)与胴长、体重、日龄之间的相关系数较高。胴长与角质颚各形态参数的关系在雌、雄个体间的差异性均显著(P0.05),体重、年龄与角质颚各形态参数的关系在雌、雄个体间的差异性均不显著(P0.05)。角质颚各形态参数与胴长、日龄之间呈线性关系;除上侧壁长外,角质颚的其它形态参数与体重之间呈幂指数关系。主成分分析认为,第一主成分解释上、下角质颚形态的贡献率分别为95.69%和95.11%,在上角质颚和下角质颚的形态参数中,载荷系数最大的形态参数分别为上脊突长和下侧壁长。研究认为,上述关系式的建立可以用于茎柔鱼的个体大小、生物量和日龄的估算。     

北太平洋东部柔鱼群体角质颚生长特性分析

角质颚是头足类重要的硬组织,蕴含着丰富的生态信息。本文根据2010年5~6月和2012年5~7月我国鱿钓船在北太平洋海域(170°E~172°W、38°N~41°N)采集的柔鱼(Ommastrephes bartramii)样本,对柔鱼东部群体的角质颚形态特征进行分析,并结合利用耳石推测的柔鱼日龄建立其生长方程。主成分分析认为,上头盖长(UHL)、上脊突长(UCL)和上侧壁长(ULWL)为柔鱼上颚的主要形态参数,下喙长(LRL)、下喙宽(LRW)和下侧壁长(LLWL)为柔鱼下颚的主要形态参数。AIC(Akaike’s information criterion)准则认为,6项角质颚主要参数与日龄的关系均以自然对数建立的生长方程为最适。分析发现,上颚生长方程的系数均大于下颚,说明上颚的生长速度大于下颚,而喙部生长方程的系数相近且最小,说明喙部生长速度较慢;上下颚比较发现,上颚头盖脊突较下颚的生长快,而喙部和翼部的生长相似。     

个体差异对西南大西洋阿根廷滑柔鱼角质颚外部形态变化的影响

角质颚是头足类重要的硬组织,广泛用于头足类分类及资源量估算等研究中。根据2010年中国鱿钓船在西南大西洋海域采集的2 916对阿根廷滑柔鱼角质颚样本,对角质颚12项外部形态参数进行测量,根据主成分分析结果,以角质颚的上头盖长(UHL)、上脊突长(UCL)、上翼长(UWL)、下头盖长(LHL)、下脊突长(LCL)和下翼长(LWL)作为角质颚各区外部形态变化的特征指标,以头盖长和脊突长之比(HL/CL)、喙长和脊突长之比(RL/CL)、喙宽与脊突长之比(RW/CL)、侧壁长和脊突长之比(LWL/CL)、翼长和脊突长之比(WL/CL)分别作为角质颚各区外形变化的指标,利用方差分析(ANOVA)和最小显著差多重比较法(LSD)研究不同性别、性腺成熟度和胴长范围对角质颚各区生长和外形变化的影响。结果表明,不同性别间UHL、UCL、UWL、LHL、LCL和LWL的变化存在显著性差异,相同性别不同性腺成熟度、不同胴长范围内的UHL、UCL、UWL、LHL、LCL和LWL的变化均存在显著性差异,而不同性别、不同性腺成熟度和不同胴长范围间上、下颚的HL/CL、RL/CL、RW/CL、LWL/CL、WL/CL的变化不存在显著性差异,并且其值基本恒定,上、下颚分别为78.04%、22.46%、17.28%、81.41%、23.07%和50.69%、43.31%、41.13%、144.98%、93.68%。研究表明,不同个体对阿根廷滑柔鱼角质颚外部形态变化有显著的影响。     

个体差异对西沙群岛海域鸢乌贼角质颚外部形态变化的影响

角质颚结构稳定、信息量大,是研究头足类渔业生物学的重要材料。根据2017年5—8月我国灯光罩网渔船在中国南海西沙群岛海域采集的860尾鸢乌贼样本,研究了个体差异对鸢乌贼角质颚外部形态变化的影响。结果显示,上头盖长(UHL)、上脊突长(UCL)、上喙宽(URW)、上侧壁长(ULWL)、下头盖长(LHL)、下脊突长(LCL)、下喙长(LRL)和下侧壁长(LLWL)可作为外形特征因子描述鸢乌贼角质颚的外形变化。方差分析(ANOVA)和最小显著性差异法(LSD)结果显示,主要外形特征因子在不同性别、不同胴长组和不同性成熟度间均存在显著性差异,但主要外形特征因子与脊突长(CL)的比值基本稳定。研究表明,在个体生长过程中,角质颚各区的比例基本稳定,胴长121～150 mm和性腺成熟度Ⅲ期可能是鸢乌贼角质颚外形生长的拐点。     

基于角质颚外部形态学的柔鱼种群判别

根据2012年5~10月在北太平洋海域(153°E~180°E,39°N~45°N)采集的柔鱼(Ommastrephes bartramii)样本,对柔鱼的两个群体(秋生群和冬春生群)的胴长(ML)、质量(BW)、角质颚等形态参数进行分析,同时利用角质颚形态参数对2个群体进行判别。结果表明,两个群体在胴长和质量上均具有显著差异,秋生群体柔鱼的角质颚所有形态参数均小于冬春生群体的均值;均数差异假设检验结果表明,两个群体在上脊突长/胴长(UCL/ML)、上喙长/胴长(URL/ML)、上喙宽/胴长(URW/ML)、上侧壁长/胴长(ULWL/ML)、上翼长/胴长(UWL/ML)、下喙长/胴长(LRW/ML)、下喙宽/胴长(LRW/ML)、下侧壁长/胴长(LLWL/ML)和下翼长/胴长(LWL/ML)的形态参数比例指标上差异显著(P0.05)。冬春生群雌、雄个体只在下脊突长/胴长(LHL/ML)上差异显著(P0.05),而秋生群雌雄个体在上脊突长/胴长(UHL/ML)、UCL/ML、ULWL/ML、UWL/ML、LHL/ML和LWL/ML上差异显著(P0.05)。逐步判别分析建立种群判别函数,判别正确率为90.9%,结合主成分分析结果建立的判别函数正确率为76.9%。利用逐步判别分析对两种群雌、雄个体建立判别函数,冬春生群的判别正确率为55.1%,秋生群为70.5%。研究认为,冬春生群和秋生群在角质颚上差异明显,可利用判别分析对两者进行有效的划分,但是进一步的种群划分需要考虑性别差异。     

短蛸繁殖行为及胚胎发育过程东海火枪乌贼角质颚的形态特征

根据2010年9月及2011年5月东海渔业资源底拖网调查资料,测定了火枪乌贼(Loligo beka)的胴长、角质颚形态指标等参数,阐述了火枪乌贼角质颚的形态特征及其长度的相对稳定性指标。结果表明,火枪乌贼角质颚的喙长(RL)、头盖长(HL)、脊突长(CL)、翼长(WL)、翼宽(WW)等长度上、下颚差异较大,其中,上、下颚HL相对于RL均存在着等速生长现象(P>0.05);CL相对于RL均存在着显著的异速生长现象(P<0.05);而WL、WW相对于RL则呈现极显著的异速生长现象(P<0.001)。上、下颚各长度指标均受生长的影响,均随胴长的增长呈极显著的线性增长趋势。RL/HL、RL/CL、HL/CL的比值非常稳定,不随胴长、体质量的变化而显著变化,可作为火枪乌贼角质颚形态特征的稳定性指标。     

养殖日本无针乌贼角质颚形态研究

通过测定不同生长阶段的养殖日本无针乌贼的体质量、胴长及角质颚形态等相关参数,对日本无针乌贼的体质量与胴长、体质量与角质颚相关参数以及胴长与角质颚相关参数的相关关系进行了分析。结果表明,测量样本的上、下颚存在较大差异,从绝对长度上看,上颚的喙长(RL)、头盖长(HL)及脊突长(CL)较下颚长,翼长(WL)较下颚短;从相对长度上看,上颚RL相对较短,长度仅为HL和CL的22.00%和15.76%,下颚的RL则为HL和CL的39.34%和20.23%,上颚的WL相对较短,仅为翼宽(WW)的142.49%,下颚的WL则为WW的240.66%;上、下颚各参数的比值中,RL/CL、HL/CL比较稳定,可作为日本无针乌贼与其它种类的种间差异性指标;日本无针乌贼的体质量与胴长存在极显著的指数相关关系(P0.01),体质量与角质颚相关参数存在极显著的指数相关关系(P0.01),胴长与角质颚相关参数存在极显著的线性相关关系(P0.01)。     

基于几何形态测量法的剑尖枪乌贼角质颚形态变化研究

研究生物体的个体发育有助于充分认识其个体形态变化规律，从而了解生物体结构的功能性与形态间的相关关系。为探究剑尖枪乌贼(Uroteuthis edulis)角质颚的生长变化规律，本研究使用几何形态测量学方法分析了不同性别及发育阶段角质颚大小和形态的差异，并揭示其背后的生态含义。结果显示，剑尖枪乌贼不同性别个体的角质颚大小在发育过程中存在一定差异，雌性个体角质颚大于雄性个体，但不同性别角质颚形态差异不显著(P>0.05)。主成分分析和薄板样条变形网格显示，角质颚形态由未成熟至成熟期呈渐变规律。在发育过程中，上、下颚的头盖和翼部变得更大，脊突更加凸出，颚角夹角逐渐变小；上颚喙部更加尖锐，但下颚喙部逐渐变得迟钝。多元回归分析显示，上颚在未成熟期形态变化较小，在亚成熟期和成熟期变化较大，亚成熟期和成熟期形态变化趋势相似；下颚在未成熟期和亚成熟期形态变化较大，成熟期形态变化较小，发育过程中形态变化趋势差异较大。研究表明，剑尖枪乌贼在发育过程中，角质颚形态随着其个体不断发育呈渐变规律，同时，角质颚存在异速生长现象，可能与剑尖枪乌贼发育过程中的摄食和环境变化有关。     

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.