四川彭州地区养殖虹鳟传染性造血器官坏死病病毒的分离、鉴定及病理学观察

近期,四川省成都彭州市某虹鳟养殖场暴发流行疾病,导致养殖虹鳟死亡率高达90%。现场采样观察发现患病鱼主要症状为背部发黑,鳔壁、腹膜严重出血,心包积液,空肠、空胃和显著肠炎。同时对病鱼进行细菌学与组织病理学检测,细菌学检查结果为阴性,病理学观察发现脾脏有典型凝固性坏死,肝脏组织广泛变性、坏死,肠道黏膜下层水肿,肠上皮充血及上皮细胞脱落坏死,脑膜和心外膜水肿。将病鱼的脾组织研磨过滤除菌后,腹腔注射60尾健康虹鳟,注射组均表现为急性死亡(累计死亡率达85%),试验鱼出现与自然发病鱼相同的症状而对照组无异常。取病鱼的脾脏组织研磨过滤后接种胖头鲤细胞(fathead minnow cell,FHM),细胞感染3 d后出现典型的细胞病变效应(CPE)。针对编码IHNV糖蛋白(Glycoprotein,G)基因进行逆转录-聚合酶链反应(RTPCR)检测显示,患病鱼、人工感染病鱼和病变细胞均为IHNV阳性,扩增序列与IHNV糖蛋白基因同源性为98.2%。对该病毒分离株的G基因进行系统发育分析,结果显示,该分离株与亚洲分离株聚为一簇,属于JRt基因型。     

四川地区一株传染性造血器官坏死病毒的分离鉴定及系统发育分析

2014年5月,四川省都江堰市某虹鳟养殖场暴发一种传染性疾病,幼鱼和鱼苗死亡率分别高达40％和80％.为探究此次疾病病因和流行规律,将病料进行解剖及细菌学检查、病理组织观察、人工感染实验、病毒分离、多重RT-PCR鉴定和系统发育分析.结果显示,病鱼主要临床症状表现为腹部膨大,体表发黑,肛门拖淡黄色黏液便,解剖见鳔壁、腹膜出血,胃胀气膨大和明显肠炎;细菌学检查为阴性;组织病理学上,头肾、肾脏和脾脏造血组织广泛性变性、坏死,肠黏膜下层嗜酸性颗粒细胞浸润与坏死,肝细胞变性、坏死形成局灶性的坏死灶,并在一些肝细胞胞浆内见嗜酸性包涵体.将病鱼的肝脏、脾组织研磨过滤灭菌后,腹腔注射20尾健康虹鳟,注射组均表现为急性死亡(累积死亡率=75％),并出现与自然发病鱼相同的症状.取病鱼组织匀浆滤菌液接种到鲤上皮瘤细胞(epithelioma papulosum cyprini,EPC),盲传3代出现典型的细胞病变效应(cytopathic effects,CPE).针对IHNV、IPNV与VHSV的多重RT-PCR检测显示自然发病鱼、人工感染病鱼和病变细胞均为IHNV阳性,扩增序列与IHNV核蛋白(nucleoprotein,N)基因同源性为99.9％.对分离株的糖蛋白基因“Mid-G”区域进行系统发育分析,结果显示该分离株与亚洲分离株聚为一支,属于JRt基因型.本研究首次报道我国西南地区养殖虹鳟中IHNV感染引起的疾病.     

四川地区一株锦鲤疱疹病毒的分离鉴定及系统进化分析

2015年5月,四川某鲤养殖场暴发一种传染性疾病,导致大面积死亡,死亡率高达80%。为研究此次疾病病因和流行规律,将病料进行解剖、细菌学检查、病理组织观察、PCR鉴定、病毒分离和系统进化分析。结果显示,发病鱼眼球凹陷,胸鳍及腹鳍出现出血斑,病鱼鳃严重坏死,肾脏肿大。细菌检查为阴性。组织病理学上,病变最明显的是鳃和肾脏。病鱼鳃丝血管扩张充血,鳃小片呼吸上皮细胞肿胀、脱落。鳃丝基部的上皮细胞大量增生,层次增多。肾小管上皮细胞组织结构紊乱,细胞肿胀,管腔变狭小,有崩裂和坏死现象。提取病鱼的肾脏和鳃组织DNA为模板,针对世界动物卫生组织(OIE)推荐的检测锦鲤疱疹病毒(KHV)的Sph基因进行PCR检测,出现的特异性扩增产物。将病鱼的肾脏和肝脏组织研磨过滤灭菌后,腹腔注射20尾健康鲤,实验组表现为急性死亡(累积死亡率为90%),出现与自然发病鱼相同的症状。将组织匀浆接种到普通鲤脑细胞系(CCB)后,盲传3代后可稳定地观察到典型的细胞病变。细胞培养物染色超薄切片电镜观察结果显示,病毒为有囊膜的球形病毒,病毒粒子直径为180~200 nm。对分离株的TK基因全长序列进行系统发育分析,证实该毒株属于KHV亚洲1型毒株。本研究首次报道我国西南地区养殖鲤中KHV感染引起大面积死亡,为KHV起源进化、分类以及疾病诊断和防控提供重要依据。     

四川地区一株锦鲤疱疹病毒的分离鉴定及系统进化分析

2015年5月,四川某鲤养殖场暴发一种传染性疾病,导致大面积死亡,死亡率高达80%。为研究此次疾病病因和流行规律,将病料进行解剖、细菌学检查、病理组织观察、PCR鉴定、病毒分离和系统进化分析。结果显示,发病鱼眼球凹陷,胸鳍及腹鳍出现出血斑,病鱼鳃严重坏死,肾脏肿大。细菌检查为阴性。组织病理学上,病变最明显的是鳃和肾脏。病鱼鳃丝血管扩张充血,鳃小片呼吸上皮细胞肿胀、脱落。鳃丝基部的上皮细胞大量增生,层次增多。肾小管上皮细胞组织结构紊乱,细胞肿胀,管腔变狭小,有崩裂和坏死现象。提取病鱼的肾脏和鳃组织DNA为模板,针对世界动物卫生组织(OIE)推荐的检测锦鲤疱疹病毒(KHV)的Sph基因进行PCR检测,出现的特异性扩增产物。将病鱼的肾脏和肝脏组织研磨过滤灭菌后,腹腔注射20尾健康鲤,实验组表现为急性死亡(累积死亡率为90%),出现与自然发病鱼相同的症状。将组织匀浆接种到普通鲤脑细胞系(CCB)后,盲传3代后可稳定地观察到典型的细胞病变。细胞培养物染色超薄切片电镜观察结果显示,病毒为有囊膜的球形病毒,病毒粒子直径为180~200 nm。对分离株的TK基因全长序列进行系统发育分析,证实该毒株属于KHV亚洲1型毒株。本研究首次报道我国西南地区养殖鲤中KHV感染引起大面积死亡,为KHV起源进化、分类以及疾病诊断和防控提供重要依据。     

四川地区一株锦鲤疱疹病毒的分离鉴定及系统进化分析

2015年5月,四川某鲤养殖场暴发一种传染性疾病,导致大面积死亡,死亡率高达80%。为研究此次疾病病因和流行规律,将病料进行解剖、细菌学检查、病理组织观察、PCR鉴定、病毒分离和系统进化分析。结果显示,发病鱼眼球凹陷,胸鳍及腹鳍出现出血斑,病鱼鳃严重坏死,肾脏肿大。细菌检查为阴性。组织病理学上,病变最明显的是鳃和肾脏。病鱼鳃丝血管扩张充血,鳃小片呼吸上皮细胞肿胀、脱落。鳃丝基部的上皮细胞大量增生,层次增多。肾小管上皮细胞组织结构紊乱,细胞肿胀,管腔变狭小,有崩裂和坏死现象。提取病鱼的肾脏和鳃组织DNA为模板,针对世界动物卫生组织(OIE)推荐的检测锦鲤疱疹病毒(KHV)的Sph基因进行PCR检测,出现的特异性扩增产物。将病鱼的肾脏和肝脏组织研磨过滤灭菌后,腹腔注射20尾健康鲤,实验组表现为急性死亡(累积死亡率为90%),出现与自然发病鱼相同的症状。将组织匀浆接种到普通鲤脑细胞系(CCB)后,盲传3代后可稳定地观察到典型的细胞病变。细胞培养物染色超薄切片电镜观察结果显示,病毒为有囊膜的球形病毒,病毒粒子直径为180~200 nm。对分离株的TK基因全长序列进行系统发育分析,证实该毒株属于KHV亚洲1型毒株。本研究首次报道我国西南地区养殖鲤中KHV感染引起大面积死亡,为KHV起源进化、分类以及疾病诊断和防控提供重要依据。     

四川地区一株锦鲤疱疹病毒的分离鉴定及系统进化分析

2015年5月,四川某鲤养殖场暴发一种传染性疾病,导致鲤大面积死亡,死亡率高达80%。为研究此次疾病病因和流行规律,将病料进行解剖、细菌学检查、病理组织观察、PCR鉴定、病毒分离和系统进化分析。结果显示,发病鱼眼球凹陷,胸鳍及腹鳍出现出血斑,病鱼鳃严重坏死,肾脏肿大。细菌检查为阴性。组织病理学观察,病变最明显的是鳃和肾脏。病鱼鳃丝血管扩张充血,鳃小片呼吸上皮细胞肿胀、脱落。鳃丝基部的上皮细胞大量增生,层次增多。肾小管上皮细胞组织结构紊乱,细胞肿胀,管腔变狭小,有崩裂和坏死现象。提取病鱼的肾脏和鳃组织DNA为模板,针对世界动物卫生组织(OIE)推荐的检测锦鲤疱疹病毒(KHV)的Sph基因进行PCR检测,出现特异性扩增产物。将病鱼的肾脏和肝脏组织研磨过滤灭菌后,腹腔注射20尾健康鲤,实验组表现为急性死亡(累积死亡率为90%),出现与自然发病鱼相同的症状。将组织匀浆接种到普通鲤脑细胞系(CCB),盲传3代后可稳定地观察到典型的细胞病变。细胞培养物染色超薄切片电镜观察结果显示,病毒为有囊膜的球状,病毒粒子直径为180~200 nm。对分离株的TK基因全长序列进行系统发育分析,证实该毒株属于KHV亚洲1型毒株。本研究首次报道我国西南地区养殖鲤中KHV感染引起大面积死亡,为KHV起源进化、分类以及疾病诊断和防控提供重要依据。     

大菱鲆内脏结节病病原的分离与鉴定

2017年8月,天津市滨海新区某养殖场大菱鲆(Scophthalmus maximus)发生病害,累计死亡率约为25%,患病鱼体表无明显症状。通过肉眼和病理组织切片观察发现,患病鱼肾脏、脾脏、肝脏和肠道存在大量圆形结节,肾脏、肝脏和脾脏组织病变明显,肾小管坏死,肝细胞脂肪变性,脾脏中存在大量的坏死细胞。此外,在脾脏和肾脏组织中发现大量的抗酸杆菌。利用传统病原菌分离方法,从具有典型症状的濒死大菱鲆肾脏组织分离到优势菌株myco-10,利用该菌株注射攻毒能导致健康大菱鲆66.7%的死亡率,且表现出与自然发病鱼相同的症状。采用16S rDNA、Hsp65、ropB基因序列分析,构建系统发育树并结合细菌形态特征、生理生化测试对菌株myco-10进行鉴定,结果显示,菌株myco-10的16SrDNA、Hsp65、ropB基因序列与分枝杆菌属细菌(Mycobacteriumspp.)相似度最高,且在系统发育树中与海分枝杆菌(Mycobacteriummarinum)和溃疡分枝杆菌(Mycobacteriumulcerans)聚为一簇,生理生化反应与海分枝杆菌一致。综合生理生化特征和基因序列分析结果,将菌株myco-10鉴定为海分枝杆菌。这是中国首例分枝杆菌引起大菱鲆病害的报道,可为大菱鲆内脏结节病的防治提供参考资料。     

嗜水气单胞菌源黄鳝出血病的组织病理学研究

应用组织学方法研究了分离自患出血病黄鳝(Monopterus albus)体内的嗜水气单胞菌(Aermonas hydrophila)人工感染健康黄鳝后引起的组织病理学变化。结果显示:健康黄鳝感染嗜水气单胞菌后发病呈急性过程,感染后15~33 h为发病死亡高峰期。黄鳝人工感染后出现的临床症状与自然发病病例相似,主要表现:体表出现出血斑、肛门红肿、腹腔充血以及各实质性器官出血、充血。人工感染黄鳝的肝脏、脾脏和肾脏的病理变化明显:肝脏出现广泛的充血、出血,肝细胞出现空泡变性、坏死;肾脏肾小管上皮的肿胀、结构的消失,肾小球出血、变性坏死;脾脏充血、出血;肠粘膜上皮脱落,基底膜排列紊乱,大量出血。结果表明,嗜水气单胞菌感染黄鳝后的病理变化主要表现为肝脏、肾脏等实质性器官充血、出血,及广泛的组织细胞变性和坏死。     

大口黑鲈肝脾肿大病病原研究

为了查明2009年10月广东省佛山地区养殖大口黑鲈(Micropterus salmoides)中暴发的传染性疾病的病原,对病鱼的肝脏、脾脏和腹隔膜进行切片电镜观察,发现细胞质中有大量病毒颗粒,切面为六角形,直径约145～150 nm,病毒为二十面体对称结构、无囊膜、似虹彩病毒的病毒粒子.用除菌的病鱼组织滤液感染健康大口黑鲈,被感染鱼死亡率达90%以上.根据已知虹彩病毒主要衣壳蛋白(MCP)基因序列设计特异引物,提取人工感染发病鱼的肝脏、脾脏、肾脏组织的DNA进行PCR扩增,将扩增片段进行序列测定与分析,结果表明该序列与已报道的鳜(Siniperca chuatsi)传染性脾肾坏死病毒(Infectious Spleen and Kidney Necrosis Virus,ISKNV)MCP基因同源性为98%.电镜观察和MCP基因测序分析结果显示,该病毒的分类地位为虹彩病毒科(Iridoviridae)细胞肿大病毒属(Megalocytivirus).     

一株虹鳟源传染性胰腺坏死病病毒的分离与鉴定

为明确引起四川石棉某养殖场饲养的虹鳟患病死亡的病原体,实验对自然发病虹鳟进行大体病变观察并对其病原体进行分离,通过人工感染实验及多重RT-PCR鉴定确定病原体WZ160509,并对病原体的主要结构蛋白VP2进行扩增分析,同时对病变组织进行组织病理学观察。结果显示,患病鱼主要临床症状表现为体表发黑,腹部膨大,挤压腹部可见肛门喷射淡黄色黏液便;剖检可见肝脏、肾脏苍白;肠道内无食物,内积黄色黏液。将患病虹鳟组织匀浆液无菌接种虹鳟鱼生殖腺细胞系(rainbow trout gonad cell line,RTG-2)细胞,盲传3代均出现典型的细胞病变。人工感染实验显示死亡率高达90%,并出现与自然患病鱼相同的症状。多重RT-PCR检测发现,自然发病鱼、人工感染鱼以及病变RTG-2细胞均为传染性胰腺坏死病病毒(infectious pancreatic necrosis virus,IPNV)阳性,其主要结构蛋白VP2基因与美国分离株基因组1型聚为一支,且同源性分析表明,WZ160509-VP2与IPNV-VP2(AY026345)的同源性最高,序列一致性为95.8%。组织病理学观察显示,患病鱼胰腺细胞空泡变性,坏死;肝细胞空泡变性,坏死;肾小球轻度炎症,毛细血管通透性增加,肾小囊腔内有红色絮状蛋白类物质渗出,肾小管上皮细胞空泡变性。研究表明,从该养殖场患病虹鳟中分离到的病毒为IPNV。     

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.