坛紫菜与Pyropia radi种间杂交重组优良品系的选育与特性分析

为获得具明显杂交重组优势的紫菜优良品系,实验以印度产紫菜Pyropia radi野生型品系(Pr-WT01,特点:藻体厚、生长慢、韧性好、壳孢子放散量多)为父本,坛紫菜诱变品系(Ph-HMC5,特点:藻体薄、生长快、韧性差、壳孢子放散量少)为母本进行种间杂交,从杂合丝状体产生的F1叶状体中选出4个综合性状优良的杂交重组品系,HR-6品系为其中的最优良品系。父本品系叶状体的绝对生长率最大值为0.39 cm/d,母本品系为5.24 cm/d,而HR-6品系高达9.27 cm/d,在日龄30~50 d期间,它的平均绝对生长率比母本品系的最大生长率还大。日龄60 d的叶状体平均体长父本品系为13.18 cm,母本品系为85.67 cm,而HR-6品系已达218.57 cm,分别是父、母本品系的16.58倍和2.55倍。日龄35 d的HR-6品系叶状体的叶绿素a含量高达9.43 mg/g,比父、母本品系分别增加了50%和20%;另外,它的总藻胆蛋白含量高达99.62 mg/g,分别是父、母本品系的2.18倍和1.74倍。日龄35 d的HR-6品系的叶状体平均厚度为26.22μm,比父本品系降低了37%,比母本品系增加了30%,叶状体的韧性明显增加。HR-6品系的壳孢子放散总量达167.72万个/贝,分别为父、母本品系的1.13和2.65倍。上述研究结果表明,HR-6品系具有生长快、品质好、壳孢子放散量大等优良性状,表现出良好的生产适用性。     

Pyropia churharii新品系的分离与特性分析

为发掘新的紫菜种质资源,通过对印度产紫菜Pyropia churharii的野生型品系(PCWT)进行人工诱变处理,分离出具有生长和品质优势的新品系PC-Y1和PC-Y2。PC-WT品系的叶状体具有过度释放单孢子和生长缓慢的特性。PC-Y1品系的叶状体基本不放单孢子,藻体呈细长型,生长很快。PC-Y2品系的叶状体放散少量的单孢子,藻体较宽大,生长较快。日龄55 d时,PC-Y1品系的叶状体平均体长为91.30 cm,PC-Y2品系为15.26 cm,而PC-WT品系仅为5.31cm,两个新品系的生长优势非常显著。日龄45 d的叶状体叶绿素a含量,PC-Y1和PC-Y2品系明显比PC-WT品系高;PC-Y1和PC-Y2品系藻红蛋白和藻蓝蛋白的总含量分别为119.32和102.29 mg/g,分别是PC-WT品系的2.74倍和2.35倍。日龄45 d的叶状体厚度,PC-WT品系为32.48μm,PC-Y1和PC-Y2品系分别为20.86和27.98μm,两个新品系明显比野生型品系薄。贝壳丝状体的壳孢子放散量,PC-Y1、PC-Y2和PC-WT品系分别为101.16、143.44和175.17万个/壳。此外,与野生型坛紫菜相比,PC-Y1品系对高温(29℃)具有更好的耐受性。PC-Y1和PC-Y2品系不仅具有与条斑紫菜相似的特性,如藻体薄、品质好、放散单孢子,而且PC-Y1品系比野生型坛紫菜更耐高温,壳孢子放散量也更大、生长快、成熟晚,具有被大规模栽培的潜力。     

坛紫菜品系间杂交分离色素突变体及其特性的初步研究

以野生选育的坛紫菜(Porphyra haitanensis)为母本,诱变选育全棕红的品系为父本进行杂交实验,从杂交子代大量叶片中,筛选出1株褐黄色素突变体、1株翠绿色与野生色相嵌的嵌合体和1株褐绿色与野生色相嵌的嵌合体。通过酶法分离突变体的营养细胞,单性生殖获得丝状体;分别使丝状体成熟并放散壳孢子,然后单株培养和筛选获得褐黄、翠绿和褐绿色子代叶状体。实验进行50 d。结果:(1)褐黄色突变体藻蓝蛋白和别藻蓝蛋白含量低;孢子囊枝的细胞较小,且大量形成时间比亲本晚15 d;幼苗培养初期日平均生长量仅为(1.22±0.28)cm,当叶片长到60 cm左右时生长优势逐步凸显,日平均生长量可达(7.50±1.18)cm;(2)翠绿色丝状体容易成熟,发育方式特殊,营养藻丝不经过藻丝加粗阶段,直接由球形细胞发育成孢子囊枝和壳孢子囊;翠绿色叶状体藻红蛋白含量低,仅有(5.513 0±1.049 6)mg/g(干品);叶状体生长快速,60 cm长的藻体日平均生长量高达(11.95±2.33)cm;(3)褐绿色突变体藻蓝蛋白、别藻蓝蛋白和藻红蛋白这3种色素蛋白和叶绿素的含量均较低;藻丝细胞短且细,叶状体生长速度较慢。     

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。     

条斑紫菜耐高温杂交重组品系的筛选与特性分析

为改善条斑紫菜优良品系TM-18藻体颜色偏红的弱点,本研究以红色型突变品系(TM-18,特点:藻体偏红色;生长快,色素蛋白含量高,具有一定的耐高温性)为父本;绿色型突变品系(OMO-1,特点:藻体绿色,生长较慢,色素蛋白含量低,耐高温性差)为母本进行种内杂交,从杂合丝状体的F1叶状体中,分离出了优良品系TW-9。通过比较它与亲本品系的特性,获得以下结果:在常温(18°C)和高温(24和25°C)下培养13 d,TW-9品系的壳孢子存活率分别为TM-18品系的1.0、1.1和1.1倍,以及OMO-1品系的1.1、4.7和7.2倍。在18°C组,3个品系的壳孢子苗畸形率无显著性差异,但在24和25°C组,TW-9品系的畸形苗率比TM-18品系分别降低了20.3%和29.5%,比OMO-1品系分别降低了74.8%和69.5%。将在18°C下培养40 d的叶状体分别置于18、24和25°C再培养10 d,TW-9品系的绝对生长率分别为TM-18品系的0.9、1.5和0.8倍,以及OMO-1品系的1.4、1.5和28倍。此外,在24°C下培养25 d或在25°C下培养10 d,OMO-1品系的藻体腐烂严重,最后完全解体;TM-18和TW-9品系藻体在24°C下培养25 d只出现轻微卷曲,但在25°C下,TM-18品系培养15 d就腐烂至完全解体,而TW-9品系培养30 d也只是轻微腐烂。在18°C下培养40 d的TW-9品系叶状体分别再在18和24°C下培养15 d,总藻胆蛋白含量分别为61.5和77.8 mg/g,分别为OMO-1品系的1.4和1.4倍,但与TM-18品系的含量相比无明显差异。在18°C下培养55 d的叶状体平均厚度,TW-9品系为25.6μm,分别比TM-18和OMO-1品系降低了13.5%和17.7%。另外,3个品系的壳孢子放散量无显著性差异。研究表明,TW-9品系不仅具有与TM-18品系相似的特性,如叶状体生长快、色素蛋白含量高、壳孢子放散量大等特性,并且它的藻体更薄、更耐高温,其颜色与野生色相近,符合生产栽培的要求,有望被培育成适宜栽培的新品种。     

条斑紫菜(Porphyra Yezoensis)自由丝体接种贝壳其生长发育特征的观察研究

将条斑紫菜自由贝壳丝状体和果孢子贝壳丝状体进行观察比较,结果发现:①前者接种后贝壳需要黑暗沉淀3d,适宜接种的最高温度为23℃,肉眼见苗时间为20d,肉眼见苗前显微镜下贝壳上查不到单丝;后者接种贝壳不需要黑暗沉淀,适宜接种的最高温度为19℃,接种5d后显微镜下可以查到丝状单丝,肉眼见苗时间为15d。②前者壳孢子放散需要流水刺激,在20.5℃开始放散,日放散量为(200~400)×104个/壳,持续时间(5~10)d;而后者壳孢子开始自然放散水温为23℃,日放散量为(10~200)×104个/壳,放散持续时间(14~16)d。③网帘采苗时,前者壳孢子的采苗密度为后者的2~3倍。④在海区的养殖过程中,前者网帘下海20d肉眼见苗,见苗前显微镜下查不到苗,未发现叶状体放散单孢子,叶状体生长速度快,叶状体上未出现硅藻斑,春节前菜平均产量为475kg/667m2,但菜体偏黄,柔韧性差;后者网帘下海3d后,显微镜下就能够在网帘上查到苗,11d肉眼见苗,叶状体0.5cm开始放散单孢子,春节前的菜质好,但叶状体生长速度慢,养殖后期叶状体上容易出现硅藻斑,春节前菜平均产量为325kg/667m2。     

条斑紫菜种内杂交优良品系的筛选与特性分析

以条斑紫菜(Pyropia yezoensis)野生型品系(Py-WT,特性:颜色好,生长慢,藻体厚,主要光合色素含量低,耐高温性差)的叶状体作为父本,红色突变型品系(Py-HT,特性:颜色较红,生长快,藻体薄,主要光合色素含量高,具一定的耐高温性)的叶状体作为母本进行种内杂交,从杂交丝状体的子一代叶状体中分离出1个耐高温的重组优良品系(HW-4)。在24℃下培养13 d,父本Py-WT和母本Py-HT品系的壳孢子存活率分别为18.3%和65.2%,而HW-4品系的壳孢子存活率为77.5%。在25℃下培养13 d,3个品系(Py-WT、Py-HT和HW-4)的壳孢子存活率分别为16.9%、47.1%和67.3%。在高温(24℃和25℃)下培养的HW-4品系的壳孢子存活率分别是Py-WT品系的4.2倍和4.0倍,是Py-HT品系的1.2倍和1.4倍。常温(19℃)培养50 d的壳孢子萌发体,在24℃再继续培养25 d,Py-WT、Py-HT和HW-4品系的叶状体平均体长分别增加了0.6、0.6和2.3倍,HW-4品系的平均体长分别是Py-WT和Py-HT品系的5.9倍和2.6倍;在25℃再培养25 d,Py-WT、Py-HT和HW-4品系的平均体长分别增加了0.3、0.4和1.5倍,HW-4品系的平均体长分别是Py-WT和Py-HT品系的5.3倍和2.1倍。另外,两个亲本品系的叶状体在高温(24℃和25℃)下培养10~15 d会卷曲和腐烂,培养至25 d时藻体严重卷曲且大面积腐烂;而HW-4叶状体在高温下培养25 d时藻体仅轻度卷曲,35 d后仍未见腐烂现象。常温(19℃)培养的HW-4叶状体分别在常温(19℃)和高温(24℃和25℃)继续培养15 d,总藻胆蛋白含量分别为76.0、111.1和132.3 mg/g,分别是Py-WT品系的3.1、2.2和2.0倍,是Py-HT品系的1.2、1.1和1.1倍,均显著高于双亲品系(P0.05)。3个品系的壳孢子放散量之间无显著性差异(P0.05)。上述结果表明,与亲本品系相比,HW-4品系的壳孢子和叶状体的耐高温性均明显提高,叶状体的生长速度和色素含量也大幅度提高,是一个生产适用性好的优良品系。     

坛紫菜养殖技术之二坛紫菜优质纯系苗种培育技术研究

坛紫菜在自然分类系统中属于红藻门、原红藻纲、红毛菜目、红毛菜科、紫菜属,在其生活史中具有2个明显的发育阶段,即叶状体阶段和丝状体阶段.叶状体是由丝状体放散出来的壳孢子萌发形成的,即日常食用的紫菜;丝状体是由叶状体放散出来的果孢子萌发形成的,多数在贝壳中生长.坛紫菜的育苗就是指叶状体成熟后形成的果孢子,通过采果孢子培育贝壳丝状体,丝状体在秋季成熟后放散壳孢子的过程.南日木平养殖场自2003年1月开始承担"坛紫菜优质纯系苗种培育技术研究"项目,现将技术总结介绍如下:     

紫菜人工栽培技术

1人工栽培紫菜的生长过程紫菜的人工栽培分丝状体培育和叶状体养成2个阶段。丝状体培育阶段：春末取成熟的叶状体经阴干刺激后,放入盛有海水的容器内放散果孢子,当放散量达到要求时,捞出叶状体。把孢子水按一定比例喷洒到已放有贝壳的培育池内，果孢子即附着到贝壳上，萌发钻人贝壳内生长成丝状体。秋季水温下降时，贝壳内丝状体成熟并放散壳孢子，将维尼仑网帘放入培养池内采苗，     

尿囊素对印度产紫菜Pyropia chauhanii单孢子放散和体细胞分化的影响

为探讨尿囊素对印度产紫菜Pyropia chauhanii单孢子形成与放散的影响,选用能释放单孢子的野生型品系(PC-WT)与不能释放单孢子的诱变品系(PC-Y1)为实验材料,用含不同浓度尿囊素的培养液分别培养来自叶状体梢、中和基部的圆盘体。结果显示,处理后6 d,不同部位的叶状体圆盘体的单孢子放散量次序为中部梢部基部;随着尿囊素浓度的增加,PC-WT品系叶状体圆盘体的单孢子放散总量呈先升后降的趋势,其中10mmol/L是促进单孢子放散的最适浓度;但尿囊素并不能使原本不放散单孢子的PC-Y1品系释放单孢子。用含20 mmol/L尿囊素的培养液培养PC-Y1品系的叶状体圆盘体,8 d后再用酶解法将其体细胞单离出来经体外培养后发现,经尿囊素处理的单离细胞发育成丝状体的百分率为66.1%,而不含尿囊素的对照组仅为15.2%,说明尿囊素对紫菜叶状体的体细胞向生殖细胞分化具一定的促进作用。     

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.