罗氏沼虾与三角帆蚌、鲢和鳙混养模式优化

研究了罗氏沼虾、三角帆蚌、鲢和鳙不同混养系统的养殖产量、饲料系数、增长率、总氮(TN)/总磷(TP)利用率和综合养殖效果,以期获得最优养殖模式。采用基于陆基围隔的比较实验方法,设6个实验组,分别为罗氏沼虾单养(G),罗氏沼虾与三角帆蚌二元混养(GH2)、罗氏沼虾、鲢和鳙三元混养(GSB),罗氏沼虾、鲢、鳙和三角帆蚌按照不同密度放养的四元混养(GSBH1、GSBH2和GSBH3),各实验组设置4个重复。结果表明:GSBH2组罗氏沼虾产量最高[(14.71±0.33)kg/32 m2],显著高于G组[(12.44±0.60)kg/32 m2,P0.01];GSBH1组饲料系数最低(1.43±0.04);GSBH1组增重率最高(4.66%±0.12%),G组最低(3.80%±0.23%);TN平均相对利用率在(0.92±0.09)~(1.60±0.23)之间,GSB组最高,G组最低;TP平均相对利用率为(0.23±0.03)~(1.46±0.32),GSBH3组最高,G组最低;综合养殖效果指数在(0.91±0.02)~(1.25±0.05)之间,GSB组最高,GSBH1组次之,G组最低,且三元、四元混养组显著大于G组和GH2组(P0.05)。研究表明,混养组能显著提高罗氏沼虾养殖的经济效益和生态效益。     

罗氏沼虾不同养殖模式对水体浮游生物的影响

通过围隔实验比较罗氏沼虾不同养殖模式对水体浮游生物的影响。实验设置6种养殖模式:罗氏沼虾单养(MP)、罗氏沼虾+浮萍(水面覆盖率5%)(PP)、罗氏沼虾+鲢(PF)、罗氏沼虾+背角无齿蚌+鲢(PMF)、罗氏沼虾+背角无齿蚌+浮萍(PMP)、罗氏沼虾+背角无齿蚌+浮萍+鲢(PMPF)。养殖64 d后,测定不同模式中浮游植物和三大类浮游动物(轮虫、枝角类及桡足类)的种类和数量。结果显示,上述6种模式中浮游植物共同优势种有4种,但优势度指数最大的浮游植物不同,MP组是锥囊藻属,有浮萍的PP和PMP组均为细小平裂藻,混养鲢的PF、PMF和PMPF组均为针杆藻。不同养殖模式无共同的浮游动物优势种。养殖模式对浮游生物密度具有显著影响,PF组浮游植物密度最高,MP组浮游植物密度最低,PF组浮游植物密度比MP、PP和PMP组分别高78%、53%和61%。相反,浮游动物密度MP组最高,PF组最低。混养鲢的PF、PMF和PMPF组浮游动物密度显著低于其他3组。研究表明,罗氏沼虾养殖中混养鲢可增加浮游植物密度而降低浮游动物密度,浮萍和鲢影响池塘优势种。     

稻田养殖沙塘鳢对稻田水体及底泥微生物群落结构及多样性的影响

为了研究养殖沙塘鳢(Odontobutis obscurus)对稻田水体及底泥的微生物群落结构及多样性的影响,2015年于浙江海盐江南四阡现代农业公司进行了沙塘鳢的稻田养殖实验,利用DGGE(Denaturing Gradient Gel Electrophoresis)技术对养殖过程中的稻田水体及底泥中细菌的16S r DNA片段进行指纹图谱分析。DGGE条带测序分析结果显示:稻田水体及底泥共检测到包括α-变形菌亚门(Alphaproteobacteria)、β-变形菌亚门(Betaproteobacteria)、γ-变形菌亚门(Gammaproteobacteria)、δ-变形菌亚门(Deltaproteobacteria)、ε-变形菌亚门(Epsilonproteobacteria)、绿菌门(Chlorobi)、酸杆菌门(Acidobacteria)、厚壁菌门(Firmicutes)、放线菌门(Actinobacteria)、蓝藻门(Cyanobacteria)等细菌门类。多样性分析结果显示,养殖沙塘鳢的稻田底泥微生物DGGE条带数多于常规养殖稻田,养殖稻田的底泥Shannon多样性指数2.86,显著高于常规稻田的2.27,同时养殖稻田养殖沟底泥的Shannon多样性指数随养殖时间由2.56变化到2.16。PCA(Principal Component Analysis)及DGGE聚类分析结果显示,养殖稻田的水体及底泥微生物群落结构与常规稻田存在较大差异。结果表明,稻田养殖环境的微生态条件可能优于常规稻田。     

鱼蚌混养对池塘水质、藻相结构及三角帆蚌生长的影响

2012年4月26日—2012年12月12日通过在鲢鳙鱼养殖池塘中放养不同密度的三角帆蚌,研究不同三角帆蚌放养比例对鲢鳙鱼养殖池塘中水质、藻相结构及三角帆蚌生长的影响。实验中,鲢鳙放养比例统一为3∶7,总密度为1.5尾/m3。三角帆蚌放养密度则设置4个水平,分别为单养鲢鳙鱼池塘(0只/m3),低密度三角帆蚌混养池塘(0.8只/m3),中密度三角帆蚌混养池塘(1.0只/m3)和高密度三角帆蚌混养池塘(1.2只/m3)。结果显示,混养三角帆蚌池塘的水化指标(TP、PO4-P、NH3-N、NO2-N和NO3-N)均显著低于单养鱼池塘。中密度三角帆蚌混养池塘除NH3-N和化学需氧量(COD)与低密度三角帆蚌混养池塘无显著差异外,其他各项水化指标均显著低于其他3个池塘,并且极显著低于单养鲢鳙鱼池塘。单养鲢鳙鱼池塘藻类平均密度均极显著高于鱼蚌混养池塘,其中在鱼蚌混养池塘中浮游植物密度与三角帆蚌密度成负相关关系。单养鲢鳙鱼池塘的浮游植物生物量均极显著低于中、高密度鱼蚌混养池塘,并且显著低于低密度混养池塘。浮游植物生物量与三角帆蚌密度成正相关关系,鱼蚌池塘中绿藻和裸藻的生物量在养殖过程中上升显著。低、中密度三角帆蚌混养池塘三角帆蚌存活率均显著高于高密度三角帆蚌混养池塘;低密度混养池塘中蚌湿重、壳长及壳宽相对增长率均为最大,显著高于中、高密度三角帆蚌混养池塘。研究表明,养鱼池塘混养三角帆蚌不仅能改善养殖池塘的水质,还能控制藻类数量,促使绿藻和裸藻等大型藻类的生长,提高养殖水体浮游植物的生物量总量,最终还能有效提高三角帆蚌的存活率及生长率。从改善水质,藻相结构,蚌成活率及生长等指标角度考虑,在鲢鳙鱼养殖池塘中,三角帆蚌最佳放养密度为1.0只/m3。     

鲢、鳙对三角帆蚌池塘藻类影响的围隔实验

以浙江金华汤溪威旺养殖基地的三角帆蚌养殖水体为研究对象,通过围隔实验比较研究了单养鲢、鳙和三角帆蚌的池塘浮游植物密度、生物量和优势种(属)组成等的差异,以及养蚌池混养鲢鳙对水体浮游植物密度、生物量以及优势种变化的影响。结果表明,养蚌(10#)围隔的浮游植物平均密度和生物量均显著高于高密度鲢(12#)围隔(P<0.05),其蓝藻数量及生物量显著高于高密度鲢(12#)和低密度鳙(13#)围隔(P<0.05),绿藻数量则显著低于低密度鲢单养(11#)围隔(P<0.05)。在鱼蚌混养的情况下,单养蚌(10#)围隔浮游植物平均数量显著高于鲢-蚌混养(15#,16#)和鳙-蚌混养(17#,18#)围隔(P<0.05),其蓝藻数量及生物量极显著高于鲢-蚌混养(15#,16#)或鳙-蚌(17#,18#)围隔(P<0.01),其绿藻数量显著低于混养高密度鲢(16#)或低密度鳙(17#)的混养围隔(P<0.05)。研究结果充分说明,鲢、鳙和三角帆蚌三者对水体藻类组成的影响有别,三角帆蚌养殖池中适当混养鲢或鳙可以有效控制蓝藻(铜绿微囊藻)的生长,促进绿藻(四尾栅藻)的生长,并最终有利于三角帆蚌的养殖,混养鲢密度的增加有利于控制藻类生长,而鳙密度的增加促进了裸藻等中大型藻类的生长。     

凡纳滨对虾和罗氏沼虾肠道微生物及抗生素抗性基因多样性分析

探究凡纳滨对虾和罗氏沼虾肠道微生物及抗生素抗性基因(antibiotic resistance genes, ARGs)种类的差异。通过高通量测序和变性梯度凝胶电泳(denaturing gradient gel electrophoresis, DGGE)技术分析2种虾肠道微生物群落结构差异和微生物多样性,并运用PCR方法检测了2种虾肠道细菌常见38种ARGs的携带情况。结果显示,获得凡纳滨对虾和罗氏沼虾肠道细菌有效序列分别为42 795和40 713条,物种注释单元(operational taxonomic unit, OTU)数目分别为124和82,分类地位明确的细菌种类分别隶属5个门、17个属和5个门、16个属。凡纳滨对虾肠道细菌的优势类群为变形菌门,所占比例为75.45%,优势菌属为副球菌属(25.83%)和不动杆菌属(25.24%);罗氏沼虾肠道细菌的优势类群是厚壁菌门(49.74%),优势菌属为乳球菌属(49.01%)和弧菌属(29.98%)。凡纳滨对虾肠道细菌(2.19)Shannon指数高于罗氏沼虾肠道细菌(1.78),表明前者肠道细菌多样性大于后者。DGGE图谱的分析结果与高通量测序一致,2种虾肠道细菌种类差异很大。PCR结果显示,凡纳滨对虾肠道细菌携带15种ARGs,罗氏沼虾肠道细菌携带14种ARGs。本实验表明凡纳滨对虾肠道细菌的群落种类多样性、OTU丰富度、物种总数和ARGs种类均高于罗氏沼虾肠道细菌,为后续肠道微生物资源的挖掘提供了理论依据。     

池塘虾蟹鱼混养技术

池塘养殖罗氏沼虾一般采用单养和虾鱼混养,与河蟹混养的报导甚少,为探索新的养殖途径,提高单位面积的经济效益,1995年我们在高邮市菱塘水产养殖场进行罗氏沼虾、河蟹及鲢、镛鱼混养试验,每0.0667公顷(亩)产罗氏诏虾105公斤,河蟹18.3公斤、鲢鳙鱼43.8公斤,毛收入5813元,收效显著。现报告如下。     

罗氏沼虾池塘高产养殖技术

１９９６年和１９９７年山东省文登市水产研究所在文登市第二淡水养殖试验场利用温泉水进行工厂化育苗成功,并进行了罗氏沼虾池塘养殖试验。１９９６年我们利用８亩新挖池塘,进行罗氏沼虾与鲢、鳙鱼混养,平均亩产罗氏沼虾５０ｋｇ,平均体长８．０ｃｍ,平均亩产鲢、鳙３０ｋｇ。１９９７年我们利用１０亩新挖池塘,进行鱼、虾混养,平均亩产罗氏沼虾７５ｋｇ,平均体长８．５ｃｍ,高产达１００ｋｇ。这些成绩填补了山东半岛地区罗氏沼虾养殖方面的空白,为半岛地区开展罗氏沼虾养殖打下了基础。现将试验情况报告如下。１试验条件１．１…     

复合池塘循环水养殖系统微生物群落结构分析

于2008年6至10月逐月调查研究了新型复合池塘循环水养殖系统各塘水体理化和微生物分子特征.通过提取水样中细菌总DNA,扩增其16S rDNA基因V3区,再经DGGE分析获得图谱,选择其中主要的13条特征条带进行克隆测序.研究结果表现为,随水流方向(Pl→P5),各循环塘溶氧(DO)和透明度(SD)依次呈明显下降趋势,而NH4~+-N,TP和COD_Mn水平呈明显上升趋势;与对照塘相比,循环塘DO和SD升高,COD_Mn和营养盐水平降低.DGGE图谱分析显示,各养殖塘微生物种类丰富,循环塘与对照塘的群落结构存在明显差异,且差异主要表现在较弱的条带上;13条特征条带的测序结果表明,池塘优势菌群分属4个门:放线菌门(Actinobacteria)、变形菌门(Proteobacteria)、蓝细菌门(Cyanobacteria)和拟杆菌门(Bacteroidetes),其中有2条属于蓝细菌门的条带特定分布于对照塘.典型对应分析(CCA)排序结果显示,DGGE图谱条带分布与理化因子密切相关.与传统池塘养殖相比,该养殖模式有助于改善养殖池塘微生态环境.本研究旨为池塘微生物群落结构及其功能关系研究提供借鉴.     

在淡水鱼类混养系统中吊养三角帆蚌对养殖产量和水质的影响

通过78 d围隔养殖实验检验了在草鱼、鲫、鲢、鳙混养系统中吊养三角帆蚌对鱼产量和水质的影响。设2个处理,处理Ⅰ混养草鱼、鲫、鲢和鳙,处理Ⅱ在处理Ⅰ基础上按鱼∶蚌=1∶1的比例配养三角帆蚌。实验期间定期采样分析浮游植物种类组成和生物量、初级生产力(P)、群落呼吸(R)、溶氧(DO)、pH、透明度(SD)、主要离子(CO2-3、HCO-3、Cl-、SO2-4、Ca2+、Mg2+)、总碱度、总硬度、氨态氮、亚硝酸态氮、硝酸态氮、活性磷、总氮(TN)、总磷(TP)、总有机碳(TOC)、高锰酸钾指数(COD M n)和生化耗氧量(BOD5)。结果发现,吊养三角帆蚌显著降低水体中Ca2+浓度,但对其他指标均无显著影响。处理Ⅱ草鱼、鲫、鲢产量略高于处理Ⅰ,而鳙产量略低于后者,表明在草鱼、鲫、鲢、鳙混养系统中按1∶1的比例配养三角帆蚌不会导致草鱼和鲫产量下降,但导致鳙产量降低。处理Ⅱ浮游植物多样性(Shannon-Weaver多样性指数、Margalef丰富度指数、Pielou均匀度指数和种类数)、P、P/R、SD和DO略高于处理Ⅰ,而氨态氮、活性磷、TN、TP、COD M n、BOD5和TOC略低于后者,表明在混养系统中配养三角帆蚌可显著降低养殖水体Ca2+浓度,同时可在一定程度上提高浮游植物多样性、P和DO并降低TN、TP、COD M n、BOD5和TOC。结果表明,在淡水鱼类混养系统中适度配养三角帆蚌可提高养殖的经济效益,同时有助于降低养殖系统内氮、磷和有机废物的积累。     

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.     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.