坛紫菜不同色素突变体的初步研究

初步探讨了坛紫菜Porphyra haitanensis褐色、褐绿色、翠绿色、红棕色、棕褐色、桔红色和紫色7种色素突变体的子一代叶状体形态特征、生长及4种主要色素含量的变化.3～4cm长的不同色泽幼苗经20d培养后的结果显示:(1)各色素突变体从长度、宽度、鲜重量和细胞厚度方面较野生坛紫菜均具有显著优势;在培养时间内,各色素突变体的长度日增长量均显著高于野生型坛紫菜;褐绿色、棕褐色和红棕色突变体在鲜重日增重率上表现出明显的优势,在第11～15天所有色素突变体的平均日增重率均高于野生型;(2)红棕色、棕褐色和紫色突变体的总藻胆蛋白含量明显高于野生型.紫色突变体的藻红蛋白、藻蓝蛋白和别藻蓝蛋白含量均为最高,其中藻红蛋白、别藻蓝蛋白含量为野生型的3倍.叶绿素含量均无明显变化.本研究结果为有效利用坛紫菜的不同色素突变体进行种质改良奠定了良好基础.     

条斑紫菜色彩突变体的诱导_分离和特性分析

条斑紫菜叶状体的原生质体经化学诱变剂－Ｎ－甲基－Ｎ’－硝基－Ｎ－亚硝基胍（ＭＮＮＧ）处理后，在它们的再生叶状体中，出现了少量色彩发生变异的点状异体。它们的色彩变异细胞呈点状无规则地与野生细胞或其它变异细胞镶嵌在一起。这类变异体的单孢子萌发成单色变异（或野生色）叶状体以及与母体相似的点状变异体。利用单色变异叶状体分离出绿色（ｙｅｌ），浅桔黄色（ｏｃｈ）以及深桔红色（ｂｕｓ）等三个突变株。突变株的叶状体活体吸收光谱以及藻红蛋白和藻蓝蛋白的含量与野生型相比均存在着明显的差异。经突变体支生型杂交实验证明，突变体ｙｅｌ和ｏｃｈ均含一个与色彩变化有关并且符合孟德尔遗传规律的隐性变异基因。相关变异基因的着丝粒距离，在突变体ｙｅｌ和ｃｏｈ中分别为１１．５和１５．８图距。     

坛紫菜减数分裂位置的杂交试验分析

利用坛紫菜人工色素突变体与野生型进行杂交试验,通过观察F1叶状体中是否出现颜色分离和颜色嵌合体来证明坛紫菜减数分裂发生的确切位置。以红色型人工色素突变体(SPY1和R10)作为母本,其特征:叶状体呈红色或桔红色,藻体薄而弹性差,无边缘刺;以野生型(wt)作为父本,其特征:叶状体呈棕绿色,藻体厚而富有弹性,有丰富的边缘刺。在杂交组SPY1(♀)×wt(♂)和R10(♀)×wt(♂))的F1叶状体中,均出现了2种亲本色和2种新颜色,它们分别为红色(R,母本色),野生色(W,父本色),浅红色(R′,比R色稍浅)和似野生色(W′,比野生色稍红)。4种颜色在F1叶状体上,出现了分离并形成了呈直线型排列的不同色块,从而产生了大量由2～4个色块组成的颜色嵌合体;单个嵌合体上的色块数最多为4块。在颜色嵌合体中,R和R′2种色块的藻体薄而弹性差,无边缘小刺,而W和W′2种色块的藻体厚而弹性好,富有边缘刺。在F1叶状体中,颜色嵌合体占95.2%～96.7%,单色叶状体只占3.3%～4.8%。上述结果说明,坛紫菜杂合丝状体产生的壳孢子,其萌发时进行的最初两次细胞分裂是减数分裂,它所产生的4个子细胞继续分裂,最终发育成含2～4个色块组成的颜色嵌合体;2种新颜色是由于在减数分裂的第一次分裂时发生了染色体交换和重组所产生的。本文使用的两个色素突变体,除含2个或2个以上的颜色变异基因外,还含有分别与藻体厚薄和边缘刺出现相关的变异基因,并且它们与颜色变异基因是连锁的。F1颜色嵌合体中的重组色块在3种主要光合色素和色素蛋白的含量、生长速度和成熟早晚等方面均表现出比亲本色块更好的特性,暗示利用色素突变体杂交方法有可能培育出坛紫菜的优良品系。     

萱藻生活史中盘状体阶段生长特性

于2006年3-5月在大连沿海萱藻[Scytosiphon lomentaria(Lyngbye)Link]的繁殖期内,采集具有多室配子囊的成熟萱藻,采用阴干刺激方法获得配子并在室内培育形成盘状体.观察结果显示,在20℃和15℃下,盘状体表面细胞生长出丝状体和叶状体.叶状体经生长后沿藻体纵轴裂开又形成了丝状体.丝状体上与基质接触的细胞进行放射状分裂形成盘状体,未与基质接触的细胞在继续分裂增加藻体长度的同时,在丝状体上形成了许多节状细胞团,节状细胞团与基质接触后向周边分裂又形成了盘状体.由丝状体形成的盘状体在15℃和10℃下培养2个月后形成了单室孢子囊.单室孢子囊成熟后经阴干刺激可放出游孢子,游孢子附着后萌发为直立管状萱藻幼苗.实验结果表明,在萱藻生活史中的盘状体阶段还存在盘状体→丝状体→盘状体与盘状体→叶状体→丝状体→盘状体2个循环.盘状体阶段这2个循环的存在,改变了从配子或合子获得盘状体的单一途径.利用丝状体游离培养生长速度快以及节状细胞团切碎后能在短时间内形成盘状体的特性,在室内进行人工增殖丝状体,当节状细胞团出现后将丝状体切碎,可以获得大量盘状体,通过室内培养使盘状体形成孢子囊并放出孢子,经孢子采苗后在室内培育出萱藻幼苗.本研究旨在为萱藻人工育苗探索一条新路.     

坛紫菜人工色素突变体的诱变与分离

坛紫菜叶状体经一定剂量的^60Cos-γ射线辐射再培养一段时间后，出现了少量色素体颜色发生变异的细胞，它们呈点状无规则地镶嵌在野生型细胞中。培养3周后，色素变异细胞分裂并形成了不同颜色的细胞块，其颜色呈桔红、桔黄、浅黄褐、浅红、紫红、紫褐、黄绿、绿色等。在辐射剂量0～1100Gy范围内，叶状体上色素变异细胞块的出现频率随着辐射剂量的增加而增加；但辐射剂量增至1．400Gy时，色素变异细胞块出现的频率反而下降，说明1100Gy是合适的辐射剂量。在同一个叶状体的不同部位上色素变异细胞块出现的频率足不同的，从基部到稍部，随着部位的上移而逐渐增加。用酶解法把含色素变异细胞的叶状体细胞单个分离出来并进行离体培养，在它们的再生体中，出现了多种单色的色素突变叶状体，从中分离到tan(红褐色)、bor(深桔红色)、ceb(紫红色)、hon(枯草色)、cac(深黄绿色)等不同颜色的纯色突变体。从各单色突变体中分离出来的丝状体，其颜色与各自的叶状体相同。各突变体的丝状体成熟后，放散的壳孢子长成单色的F1叶状体，其颜色与各自最初的母体叶状体相同，说明所得到的上述突变体是稳定的色素突变体。     

坛紫菜诱变育种的初步研究

近十几年来,坛紫菜品种退化、产量降低、质量下降,本实验通过诱变处理,筛选和培育优质高产的坛紫菜新品系.坛紫菜野生丝状体经一定剂量60Co-γ射线辐照后,子代叶状体发生了变异,经大量培养后筛选出紫色突变体(3号Ⅰ)和经济性状优良的个体(7号Ⅰ和7号Ⅱ),通过体细胞酶解和单克隆技术快速获得诱变选育纯系,并对其主要经济性状进行了研究.其主要特征:[1]7号Ⅰ:叶片宽[(2.99±0.61)cm]、生长快(30cm以上的藻体长度平均日增长量可达6.51cm,比对照组快55.3%)、耐高温(29℃正常生长,比对照组高2℃以上)、总藻胆蛋白含量高(104.86mg·g-1干品,比对照组高39.0%);[2]7号Ⅱ:藻体窄、生长快(30cm以上的藻体长度平均日增长量可达4.26cm,比对照组快58.7%)、叶片薄(藻体中部厚度仅为22.5～27.5μm,比对照组薄29.6%)、总藻胆蛋白含量高达104.24 mg·g-1干品,比对照组高39.4%);[3]3号Ⅰ:藻体紫色,叶片薄,藻体中部厚25.0～32.5μm;[4]7号Ⅰ和7号Ⅱ在生产上应用,产量分别达309.6kg·666.6m-2和291.5kg·666.6m-2,比对照组高37%和29%.     

二氧化锗对共培养萱藻丝状体和硅藻生长的影响

为抑制萱藻丝状体保存和扩增过程中出现的小伪菱形藻与碎片菱形藻的生长,本实验应用实验生态学方法,分别建立了丝状体与小伪菱形藻、丝状体与碎片菱形藻、丝状体与小伪菱形藻和碎片菱形藻的共培养体系,研究了1.00～4.00μg/mL二氧化锗(GeO_2)对共培养条件下丝状体生长发育及附生硅藻生长的影响。结果显示:(1)处理萱藻丝状体和硅藻共培养体系的适宜GeO_2浓度为1.00～2.50μg/mL,各实验组14 d的硅藻抑制率均高于67.33%±5.18%,且丝状体生长发育良好,2.00μg/mL为最适浓度,此浓度下丝状体日均增长率最高,在各培养体系中均大于11.00%,且诱导后孢子囊枝比例和孢子囊直径分别为57.47%±5.31%和(24.55±1.01)μm,与对照组差异不显著;(2) 3.50和4.00μg/mL GeO_2虽对硅藻抑制效果更佳,但同时也会抑制丝状体生长和后期孢子囊的形成与发育,其中4.00μg/mL GeO_2可导致丝状体死亡;(3)碎片菱形藻较小伪菱形藻对GeO_2更敏感。实验14 d,各浓度GeO_2对碎片菱形藻的抑制率为(82.10%±2.40%)～(96.35%±0.79%),均高于同浓度GeO_2对小伪菱形藻的抑制率;同时在丝状体与小伪菱形藻和碎片菱形藻的共培养体系中,碎片菱形藻占硅藻比例随GeO_2浓度升高而相应下降。     

条斑紫菜优良品系(LC-14)的筛选与特性分析

从条斑紫菜(Pyropia yezoensis)绿色突变体和红色突变体种内杂交产生的F_1叶状体中,分离出新品系LC-14。该品系的F_1叶状体在生长速度和品质等方面均显著优于条斑紫菜野生型栽培品系(WT)。日龄70 d的叶状体平均长度和湿重,LC-14品系分别为106.53 cm和3.07 g,分别是WT品系的4.39和10.27倍。培养至第55天,LC-14品系的3种主要光合色素(叶绿素a、藻红蛋白和藻蓝蛋白)含量分别为9.85 mg/g、52.09 mg/g和23.26 mg/g,分别比WT品系提高了65%、65%和49%,而其藻体的平均厚度(20.89μm)反而降低了32%。此外,LC-14品系的壳孢子放散总量为761.32×10~4 ind/壳,是WT品系的1.28倍。上述结果表明,LC-14品系具有生长快、品质优、壳孢子放散量大的优点,藻体颜色与野生色(棕褐色)相近,是条斑紫菜的优良品系,有望在生产中应用。     

坛紫菜优质新品系（Q-1）主要经济性状的研究

对杂交选育的坛紫菜优质品系（Q-1）和人工养殖的坛紫菜（对照组）进行叶状体生长、藻体厚度、4种色素含量、粗蛋白、氨基酸含量的测定以及丝状体的生长发育等实验。结果表明，（1）（Q-1）F2、F3叶状体生长迅速，不易成熟；3～4cm的F。叶状体经过10～15d的培养，平均日增长量高达（8．33±1．01）cm，分别为父、母本的1．4和2．7倍；（2）F3叶状体在第1次剪收时藻体厚度为（21．0±1.5）μm，仅为对照组厚度的52％，第2次剪收时为（25．6±1．9）μm，为对照组的56％；F2剪收1次后藻体的长度、宽度和鲜重平均日增长量分别为对照组的2．1、2．4和2．2倍；（3）F2叶状体的总藻胆蛋白含量为（109．52±0．94）mg／g，为对照组的1．6倍；粗蛋白的含量高达（41．71±．11）g／100g，比对照组高27％；F。叶状体第1次剪收时叶绿素a的含量高达（7．66±0．19）mg／g，比对照组高13％；（4）F3叶状体第1次剪收时呈味氨基酸中鲜味氨基酸与甜味氨基酸的总量为2．49g／100g，为对照组的1．8倍；必需氨基酸含量为15．66g／100g，比对照组高13％；（5）（Q-1）和对照组的丝状体在29℃分别培养30～40d时，90％的营养藻丝发育成孢子囊枝。     

铁促进半叶紫菜华北变种丝状体的生长发育及其生理生化基础

通过探讨半叶紫菜华北变种(Pyropia katadae var. hemiphylla)丝状体在不同铁浓度下的相对生长速率(RGR)、孢子囊枝形成率及若干生理生化指标(叶绿素荧光参数、活性氧含量、抗氧化剂含量、抗氧化酶活性等)的变化规律,以期获得适宜其生长及孢子囊枝形成的铁浓度范围,并初步揭示其在不同铁浓度下的生理生化变化特征。研究结果显示,在0.040 mg/L铁浓度下,半叶紫菜华北变种营养藻丝有较高的RGR、光系统Ⅱ最大量子产量(Fv/Fm)和调节性能量耗散的量子产量[Y(NPQ)],表明此铁浓度可促进营养藻丝的光能转换效率和光保护能力的提高,并利于其生长。高铁浓度(0.160~0.800 mg/L)组的营养藻丝RGR显著降低,而贝壳丝状体孢子囊枝形成率显著增加,表明高铁浓度抑制了藻丝的营养生长,而促进了藻丝营养生长状态向发育状态的转变。贝壳丝状体的孢子囊枝比例与Fv/Fm呈显著的正相关关系,表明营养藻丝向孢子囊枝转变后,贝壳丝状体的光能转换效率显著提高。铁的添加使藻丝中活性氧(ROS)含量显著增加,而类胡萝卜素和脯氨酸含量以及抗氧化酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)、谷胱甘肽还原酶(GR)]活力与ROS含量均呈显著正相关关系,表明藻丝的抗氧化系统可对铁介导的过量ROS作出积极应答,以平衡ROS的产生和清除。本研究可为半叶紫菜华北变种的苗种培育提供理论依据。     

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.