菲律宾蛤仔家系的建立及早期生长发育

采用不平衡巢式设计建立33个菲律宾蛤仔家系(11个父系半同胞家系和33个全同胞家系),并对各家系蛤仔的卵径、受精率、孵化率及生长、存活和变态的相关指标进行了分析。结果表明:各家系蛤仔的卵径、受精率无显著差异(P>0.05,n=90),但孵化率有明显差异(P<0.05,n=90)。在不同时期各家系蛤仔的生长情况不同。幼虫期间,9日龄C2生长最快比生长最慢的F2平均壳长大28.24%,且差异显著(P<0.05,n=90)。D3绝对生长最大比平均值高37.24%。稚贝期间,40日龄I1生长最快比生长最慢的B3平均壳长大78.29%,且差异显著(P<0.05,n=90)。I1绝对生长也最大比平均值高87.61%,其中400～500μm个体占30%,500μm以上个体占53.33%,家系内个体趋于大型化,而B1、B3家系内个体生长性状出现衰退现象,趋于小型化,300μm以下个体分别占整个家系的83.33%、90%。在相同时期各家系蛤仔的存活率不同。幼虫期间,9日龄I2存活率最高比平均存活率高94.14%,E3存活率最低比平均存活率低72.65%。稚贝期间,40日龄时各家系稚贝的存活率较高,都在85%以上。变态期间,同胞...     

菲律宾蛤仔獐子岛群体两种壳型表型性状比较

以大连獐子岛野生菲律宾蛤仔为材料,对"壳宽型"、"壳扁型"蛤仔两个壳型的壳长、壳宽、壳高、活体质量、软体质量、产卵量及其子代的生长和存活进行比较。试验结果表明,相同壳长的两种壳型蛤仔,"壳宽型"蛤仔的活体质量及软体质量均显著高于"壳扁型"蛤仔(P0.05);两种壳型蛤仔的壳宽均是影响活体质量的主要因素,壳长均是影响软体质量的主要因素;两种壳型蛤仔初孵D形幼虫、3日龄、6日龄幼虫壳长生长差异不显著(P0.05);15日龄"壳扁型"蛤仔幼虫壳长生长显著快于"壳宽型"蛤仔(P0.05);稚贝期,除30日龄外,"壳宽型"蛤仔壳长生长显著快于"壳扁型"蛤仔(P0.05);"壳宽型"蛤仔幼虫及稚贝期存活率均显著高于"壳扁型"品系(P0.05)。     

胶州湾移植底播菲律宾蛤仔的生长和死亡特性

2004年5月至2005年4月对胶州湾菲律宾蛤仔（Rudimpes philippinarum）底播增殖区进行了逐月定点采样，将样品带回放于实验室内水族箱暂养，每站随机取样，共对3269个个体进行了基本生物学特性测定，研究了移植底播菲律宾蛤仔的生长、死亡等渔业生物学特性。结果表明，底播增殖菲律宾蛤仔苗种的平均个体质量0．26g、平均壳长11．1mm；底播蛤仔与野生蛤仔在生长规律上基本一致，春末至秋初（4～9月）是其主要生长期；1～3龄期间个体生长速度较快，1～2龄、2～3龄，个体质量分别增长3．88g和4．02g；1～2龄生物量增长最快，2～3龄由于死亡率增大，其生物量增长缓慢；1～3龄蛤仔软体部的生长速度快于贝壳，5～6月是菲律宾蛤仔的繁殖肥育期。根据个体生长特性，3龄为最佳采捕年龄；根据目前的养殖状况，2龄蛤仔已达到商品规格，从生物量上分析，采捕2龄蛤仔收益最高；6月是最佳的捕获时期。蛤仔生长具有明显的季节变化，水温是影响菲律宾蛤仔生长的主要环境因子。[中国水产科学，2006，13（4）：642—649]     

胶州湾菲律宾蛤仔个体生长模型的构建与验证

为更好地掌握胶州湾菲律宾蛤仔(Ruditapes philippinarum)的动态生长情况，本研究基于动态能量收支(Dynamic energy budget, DEB)理论，利用python软件构建了菲律宾蛤仔的个体生长模型，以2018年4月24日~2019年1月9日观测的胶州湾海域叶绿素a和水温为强制函数，通过现场实验和已有文献报道获取模型参数，模拟了菲律宾蛤仔软体组织质量和壳长的生长情况，并根据胶州湾海域菲律宾蛤仔生长的实测数据对模型进行了验证。结果表明，构建的个体生长模型能够很好地模拟胶州湾海域菲律宾蛤仔软体组织干重和壳长的生长，软体组织干重和壳长的模拟值与实测值呈显著线性相关关系(P<0.01)，R2分别为0.9374和0.9168。敏感度指数最高的是阿伦纽斯温度TA和参考温度T1，如果TA和T1分别改变10%，菲律宾蛤仔软体组织干重增加高达8.86%。研究结果为后续开展基于生态系统动力学模型的养殖容量动态评估提供了基础模块和数据支撑。     

不同近交系数蛤仔橙色品系的生长和成活研究

以不同遗传背景的蛤仔（Ruditapes philippinarum）橙色品系为材料,采用建立半同胞家系子一代H1（F=0.125）、全同胞家系子一代F1（F=0.250）、全同胞家系子四代F4（F=0.594）及自然对照组C1（F=0）的方法,进行了不同近交系数蛤仔橙色品系生长和成活的研究.结果表明,在整个养殖周期中F1组的壳长生长最慢,在稚贝期和养成期均显著小于F4和C1组（P＜0.05）,H1、F4和C1组之间的壳长生长差异不显著（P＞0.05）.C1组的成活率在整个养殖周期中为最小,除幼虫期3日龄外,其他各日龄均显著小于其他试验组（P＜0.05）,而H1、F1和F4组之间的成活率则差异不显著（P＞0.05）.试验组F1壳长生长的衰退率为2.92％ ～ 18.33％,平均值为（12.05±6.54）％,试验组H1在稚贝期、养成期显现出一定的衰退现象,而试验组F4在整个养殖周期中均未表现出近交衰退现象;各试验组的成活性状在各日龄均未出现近交衰退.该研究为橙色品系的选育奠定一定的理论基础.     

不同地理群体菲律宾蛤仔的选择反应及现实遗传力

对不同地理群体的3龄菲律宾蛤仔(Pp莆田群体、Dp大连群体、Tp东京群体)进行了混合选择。测量了各实验组的壳长,计算了不同地理群体菲律宾蛤仔的选择反应和现实遗传力。结果表明,3个地群体菲律宾蛤仔子代的上选组壳长显著大于对照组(P<0.05)。在不同生长发育阶段,菲律宾蛤仔的选择反应(R)和现实遗传力(hR2)随着日龄的增大而减小,即R幼虫培育期0.804±0.084>稚贝期0.705±0.039>养成期0.671±0.024;hR2幼虫期0.458±0.051>稚贝期0.402±0.025>养成期0.382±0.013。从总体水平上分析,菲律宾蛤仔R为0.726±0.1074,莆田群体、大连群体、东京群体的R分别为0.758±0.101、0.690±0.049、0.732±0.059;hR2为0.414±0.044,莆田群体、大连群体、东京群体的hR2分别为0.432±0.058、0.393±0.028、0.417±0.033。地理群体间的R和hR2次序为莆田群体>东京群体>大连群体,且彼此间无显著差异。     

桑沟湾楮岛大叶藻床区域菲律宾蛤仔的生态贡献

桑沟湾楮岛大叶藻(Zostera marina L.)床周边存在大量的底栖菲律宾蛤仔(Ruditapes philippinarum),为摸清菲律宾蛤仔的生理活动与大叶藻的相互作用,2016年5~7月,在菲律宾蛤仔和大叶藻集中分布区,评估了菲律宾蛤仔种群资源量,现场流水法测定了菲律宾蛤仔个体水平的摄食、代谢生理,围隔实验法探讨了种群水平蛤仔与大叶藻的相互作用。结果显示,桑沟湾楮岛大叶藻床海区菲律宾蛤仔的平均生物量为(572.00±20.23) ind./m2,大(壳长为3.50~4.10 cm)、中(壳长为3.00~3.50 cm)、小(壳长为2.00~3.00 cm)规格各占9.01%、43.60%和47.38%。菲律宾蛤仔的排氨率、耗氧率、滤水率、摄食率分别为(0.44±0.15)~(1.40±0.35) μmol/(ind.·h)、(0.21±0.02)~(0.33± 0.08) mg/(ind.·h)、(0.69±0.38)~(0.83±0.66) L/(ind.·h)和(2.57±0.41)~(3.41±0.68) mg/(ind.·h),且都随体重的增加而增大。围隔实验设有3个实验组(蛤仔组、大叶藻组和大叶藻+蛤仔组),1个空白组,每组3个平行(大叶藻30茎枝左右、蛤仔15个左右),实验进行4 h。研究表明,蛤仔组、大叶藻+蛤仔组和大叶藻组间的溶氧浓度存在显著差异(P<0.05);蛤仔组与其他3组的氨氮浓度存在显著差异(P<0.05);蛤仔组、大叶藻+蛤仔组与空白组的水体颗粒物浓度存在显著差异(P<0.05),大叶藻组与空白组差异不显著(P>0.05)。桑沟湾楮岛海区菲律宾蛤仔养殖面积约为0.5 km2,蛤仔每天可以过滤46 t海水中的悬浮颗粒物,并为大叶藻提供0.4 t的氨氮。本研究为深入揭示大叶藻海区菲律宾蛤仔的生态作用提供了基础数据。     

不同地理群体菲律宾蛤仔表型性状的相关性与通径分析

随机选取繁殖时期的南方群体北方养殖菲律宾蛤仔(SN)、北方土著品种(NN)和南方群体南方养殖蛤仔(SS),测量其壳长(SL)、壳高(SH)、壳宽(SW)、活体质量(mL)、软体质量(mM)和烘干后软体部干质量(mF),采用相关与通径分析方法分析不同地理群体的菲律宾蛤仔表型性状对软体质量的作用效果,为菲律宾蛤仔的选择育种提供理论依据和测度指标。试验结果表明,不同地理群体菲律宾蛤仔的形态学指标无显著差异(P>0.05);不同地理群体各数量性状之间的相关关系均达到极显著水平(P<0.01);决定系数分析表明,不同地理群体菲律宾蛤仔影响软体质量的主要表型性状并不相同,南方群体北方养殖蛤仔群体的壳宽直接作用最大,壳宽通过壳高的间接作用是次要因素;北方土著品种群体壳长是主要因素,壳长通过壳高的间接作用是次要因素;南方群体南方养殖蛤仔群体壳高的直接作用是主要因素,壳长通过壳高的间接作用是次要因素。对通径系数检验不显著的自变量进行删除,利用逐步回归的方法,建立不同地理群体菲律宾蛤仔软体质量的最优回归方程:SN群体,mM1=-4.276+0.211SH+0.116SW;NN群体,mM2=-2.806+0.088SL+0.087SH;SS群体,mM3=-3.101+0.290SH。回归方程分析表明回归关系均达到极显著水平(P<0.01)。     

波纹巴非蛤早期发育的扫描电镜观察

本实验使用扫描电镜显微技术观察了波纹巴非蛤胚胎发育和幼虫发育变态的早期发育过程,并获得了清晰的电镜照片,描述了波纹巴非蛤配子、胚胎和早期幼虫发育的形态变化特征。观察结果还表明,波纹巴非蛤卵子卵径为58.49μm,D形幼虫壳长87.38μm,附着幼虫壳长为200~220μm,以上形态规格均小于菲律宾蛤仔、缢蛏和硬壳蛤等双壳贝类。     

不同壳色菲律宾蛤仔品系F2的表型性状

于2007年9月,对选育的菲律宾蛤仔不同壳色品系(C:对照组;Tr:两道红品系;Tw:两道白品系;Ab:玛瑙黑品系;Or:海洋红品系;Pw:珍珠白品系;Z:斑马蛤品系;W:波纹蛤品系)F₁和F₂的表型性状进行了研究。结果表明,1龄F₁的壳长以Pw最大,与Tr差异不显著(P>0.05),明显大于对照组及其它品系,Z壳长最小且与其它品系差异显著((P<0.05),C的壳长明显小于Tw、Ab((P<0.05),但与Or、W差异不显著((P>0.05);F₁鲜重也以Pw最大,Z最小,且与其它品系差异显著(P<0.05),Tr、Tw、Ab和Or鲜重差异不显著((P>0.05),但明显大于C((P<0.05);F₁产卵量Pw、Tr明显高于其它品系,Z、C明显小于其它品系((P>0.05),Tw、Ab、Or和W彼此差异不显著((P>0.05);F₂的表型性状,C的孵化率低于其它品系((P<0.05),但与Tw无显著差异((P>0.05),各壳色品系间卵径、受精率和D形幼虫大小差异不显著((P>0.05)。浮游期结束时(9日龄),W与Z幼虫壳长明显大于其它品系((P<0.05),Tw、Ab、Or、Pw、Z彼此间差异不显著((P>0.05);幼虫存活率大小顺序为,Ab、Z>Or、W>Tw、Pw >Tr>C,彼此差异显著((P<0.05)。变态时间和变态规格各品系间无显著差异((P>0.05),变态率大小的顺序为Ab>Z>Tw>Or>Pw>W>Tr>C,彼此差异显著((P<0.05)。室内培育阶段结束时(240日龄),Ab壳长最大,但与Or、Tr差异不显著,Z壳长最小,但与C、W差异不显著((P>0.05),C与Pw、W,Tr、Tw、Or之间,以及Tw与Pw差异也不显著;Z的存活率最高,明显高于除Ab外的其它品系,C的存活率最低,明显低于除Tr、Tw外的其它品系,W>Or>Pw,彼此差异显著((P<0.05)。360日龄时,Pw壳长和鲜重最大,显著大于其它壳色品系((P<0.05),Ab和Z壳长和鲜重显著小于其它壳色品系((P<0.05);Ab和Z的存活率高于其它品系((P<0.05),但与Or、Pw差异不显著((P>0.05),Or存活率高于C((P<0.05),其它各品系存活率无显著差异((P>0.05)。从相对产量上看，Z(678.63%±56.80%)>Ab(554.88%±69.42%)>Or(527.23%±76.21%)>W(475.97%±90.25%)>Pw(405.90%±55.19%)>Tw(224.89%±47.85%)>Tr(178.50%±34.50%)>C(100.00%±22.10%)。     

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.     

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.     

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.