栉孔扇贝人工雌核发育的细胞学观察

运用荧光显微镜观察了栉孔扇贝正常卵子与雌核发育卵子在受精和成熟分裂过程中的核相变化。结果表明,尽管紫外线照射没有影响受精卵的成熟分裂以及雌性、雄性原核的形成,但使雌核卵的发育速度出现明显的滞缓。在第1次卵裂中期,雌核发育卵子中的雄性原核没有像雌性原核那样形成染色体,而是浓缩为一染色质小体(DCB),游离在细胞质中,不参与核分裂。胞质分裂结束时,DCB位于2个卵裂球之一的细胞质内或在赤道板处被分割成两部分。实验结果首次提供了栉孔扇贝雌核发育的细胞学证据。     

栉孔扇贝雄核发育二倍体的人工诱导

研究了利用6-二甲基氨基嘌呤(60μg/mL;6-DMAP)抑制第1卵裂诱导栉孔扇贝[Chlamys farreri(Jones et Pre-ston)]雄核发育二倍体的条件。雄核发育单倍体是将强度为2.8 mW/(cm2.s)的紫外线照射20 s的卵子与正常精子受精后得到的。6-DMAP不仅可以有效地抑制减数分裂,还可以有效地抑制有丝分裂;抑制第1卵裂的适宜起始时间为受精后80 min,诱导率为21.0%~22.6%。细胞学观察显示,6-DMAP抑制第1卵裂产生的雄核发育二倍体主要来源于第1卵裂中期的受精卵,由于阻止了染色体分离和原核移动,导致一个融合的二倍性雌性原核的形成;经紫外线照射的卵核在第1卵裂中期没能形成染色体,而是形成1个浓缩的染色质小体,没有参与第1卵裂后期的核分裂。尽管倍化率和D形幼虫发生率较低,但本研究证实了栉孔扇贝雄核发育二倍体人工诱导的可行性。[中国水产科学,2006,13(4):585-590]     

异源精子诱导栉孔扇贝雌核发育二倍体的微管动态变化

采用紫外线遗传灭活的长牡蛎（Crassostrea gigas）精子激活栉孔扇贝（Chlamys farreri）卵子,并用6-DMAP诱导染色体加倍的方法,获得第二极体抑制型雌核发育二倍体早期胚胎。多聚甲醛固定、免疫荧光染色后,运用荧光显微镜观察栉孔扇贝正常发育卵子和异源精子诱导的雌核发育卵子,对其受精过程中微管的动态变化过程进行观察和分析。结果表明：（1）正常发育组受精卵内以微管为基础的纺锤体能够顺利地组装并引导卵细胞进行减数分裂和第一、第二极体的排放,以及雌、雄原核融合和第一次卵裂;（2）异源精子诱导雌核发育的卵子经6-DMAP处理后,部分微管变得模糊或消失,纺锤体受到破坏导致染色体的分离无法进行,第二极体的形成受到抑制并使雌核染色体二倍化;去除6-DMAP作用后,微管重新组装,雌核分裂重新启动继而进行卵裂;精核保持固浓缩状态或轻微膨胀形成雄性原核,但卵裂后期则以致密的染色质体（DCB）形式存在于分裂沟上或进入一个卵裂球中。结果证实,长牡蛎精子经紫外线遗传灭活后可顺利进入并激活栉孔扇贝成熟卵子但不参与合子核的形成,6-DMAP也可有效抑制第二极体的排放而获得雌核发育二倍体胚胎。本实验结果为研究异源精子诱导栉孔扇贝雌核发育的可行性提供了细胞学依据。     

栉孔扇贝（♀）×长牡蛎（♂）受精过程的荧光显微观察

采用二氨基苯基吲哚(DAPI)染色荧光显微方法,对栉孔扇贝(Chlamys farreri♀)×长牡蛎(Crassostrea gigas♂)受精过程进行详细观察。结果显示,长牡蛎精子能迅速附着并穿过栉孔扇贝卵膜,精核发生解凝缩而膨胀形成雄性原核;精子入卵后,栉孔扇贝卵子减数分裂重新启动,释放极体并形成雌性原核,最后雌、雄原核融合,受精卵开始第1次卵裂。栉孔扇贝与长牡蛎杂交受精率一般在40%左右。受精卵发育过程中出现了排放2个极体、排放1个极体、不排放极体3种类型,所占受精卵比例约为65%、25%和10%。多数受精卵第1次卵裂后期,染色体发生异常分离,不能平均分配到2个子细胞中,这可能是造成早期胚胎畸形,只能发育到担轮幼虫阶段而全部死亡的主要原因。     

栉孔扇贝异精雌核发育四倍体早期胚胎发育的细胞学荧光显微观察

用1500μW/cm2的紫外线照射长牡蛎(Crassostrea gigas)精子60 s以进行灭活处理,并使之与栉孔扇贝(Chlamys farreri)卵子受精,在卵子受精后排出第一极体前用6-DMAP(50 mg/L)处理受精卵,持续处理35 min,抑制第一极体和第二极体的排放,诱导异精雌核发育四倍体。采用二脒基苯基吲哚(DAPI)荧光染色显微观察法,对灭活的长牡蛎精子诱导的栉孔扇贝雌核发育四倍体早期胚胎发育过程进行细胞学观察。结果表明:经紫外线灭活过的长牡蛎精子进入栉孔扇贝卵子后发生轻微膨胀;在第一次卵裂中期,精核形成一致密的染色质小体(DCB),位于两组分开的母本染色体之间,不参与核分裂;第一次卵裂结束时DCB滞留于两卵裂球的分裂沟上或进入其中一分裂球中;第二次卵裂过程中,DCB的去向与第一次卵裂时基本一致。6-DMAP处理有效地抑制了第一极体和第二极体的排出,从而使雌核四倍化。对担轮幼虫染色体倍性分析结果表明,通过本方法可以获得6.25%的四倍体幼虫。本研究还对灭活的异源长牡蛎精子诱导栉孔扇贝雌核发育四倍体过程中产生的复杂倍性、核物质分离紊乱及多精附卵现象进行了观察和分析。     

栉孔扇贝正常发育和人工雌核发育二倍体早期胚胎核行为的细胞学观察

采用Bouin氏液固定、石蜡切片和苏木精-伊红染色方法，在光镜下对栉孔扇贝正常发育和6-DMAP第二极体抑制型雌核发育二倍体卵在受精和第一、二次卵裂过程中的核相变化进行了详细观察。结果表明，正常发育卵内的雌、雄原核能融合为合子核，而雌核发育卵内的精核、雌核变化相当复杂。精核至少存在两种状态：（1）精核只在刚入卵时发生轻微膨胀，以后保持固缩状态，不膨大形成雄原核；（2）在第二次成熟分裂之后，精核再次去浓缩膨胀，但其体积并未达到正常雄原核的大小。在第一、第二次卵裂过程中，此精核不参与核分裂，以致密的染色质体（DCB）存在于两组分开的母本染色体之间，卵裂结束时滞留于两卵裂球的分裂沟上或进入其一的细胞质中。受精卵经6-DMAP处理，雌核形成第二极体的过程受到有效抑制，导致雌核二倍化。此外，作者对实验中出现的多精入卵和多极分离现象进行了观察和分析。     

栉孔扇贝♀和长牡蛎♂杂交受精及早期胚胎的细胞学研究

以栉孔扇贝Chlamys farreri为母本、长牡蛎Crassostrea gigas为父本进行人工杂交。采用Bouin氏液固定、石蜡切片和苏木精-伊红染色在光镜下对其受精和第1次卵裂过程中核相变化进行观察;运用压片法和热滴片法分别对4～8细胞期和担轮幼虫期胚胎进行染色体制片。结果表明,长牡蛎精子可以进入栉孔扇贝卵子,并激活卵子减数分裂使其释放第1极体（PB1）和第2极体（PB2）,能够形成雌、雄原核并融合为合子核,接着受精卵开始第1次卵裂;杂交胚胎发育过程中,囊胚期很长、胚胎畸形严重,只能发育到担轮幼虫期;杂种胚胎染色体数目变化范围较大,在20～85之间,染色体不能平均分配到两个子细胞中是杂种胚胎死亡的主要原因。杂交胚胎不能存活保证了异源精子诱导栉孔扇贝雌核发育的可靠性。     

紫外线诱导栉孔扇贝雄核发育的研究

研究了利用紫外线诱导栉孔扇贝雄核发育的条件。表明紫外线(254nm)对卵子染色质失活是有效的。在强度为2.8mW·cm-2·s 1的紫外线下照射20s的卵子与正常精子混合后能保持一定的受精率(60.2%),且D形幼虫发生率为0。染色体检查结果显示此时单倍体率最高(49.2%)。说明在强度为2.8mW·cm-2·s-1的紫外线下照射20s是获得雄核发育单倍体的适宜条件。研究发现受精率和D形幼虫发生率随照射时间的增加而下降,遗传失活的卵子与正常精子受精后其胚胎发育至D形幼虫前期停止。实验中各处理组均出现非整倍体。出现的原因可能由于紫外线照射剂量对卵子染色体遗传失活的作用程度不同以及DNA的光修复。     

6-DMAP诱导栉孔扇贝三倍体的细胞学观察

用Bouin氏液固定、连续石蜡切片方法,对6-二甲基氨基嘌呤(简称6-DMAP)抑制第二极体诱导栉孔扇贝三倍体在受精和早期卵裂过程中的细胞学变化进行了详细观察。结果表明,在授精后25min,以60mg/L的6-DMAP处理栉孔扇贝受精卵15min,有效地破坏了纺锤体结构的形成,抑制了第2次减数分裂进程,致使受精卵内形成两种核相:一种是1个大的二倍性雌核和1个雄核;另一种是两个单倍性的雌核和1个雄核。不论形成几个雌原核,它们都能与雄原核相互靠近,在卵轴中央核膜逐渐发生融合,形成合子核,三倍体的合子核在卵内所占体积明显较二倍体的大。继而,合子核经过DNA复制,最后凝缩成染色体,发生有丝分裂,其过程与正常二倍体相同。     

缢蛏受精和早期卵裂过程的细胞学变化观察

采用普通光镜、荧光显微镜和石蜡切片技术,对缢蛏受精和早期卵裂过程中的精子入卵、减数分裂、雌雄原核形成与结合、早期卵裂以及多精入卵等细胞学事件进行了显微观察。结果表明,缢蛏成熟未受精卵多呈圆球形或卵圆形,少数呈梨形,卵径为82～88μm,核相处于第一次成熟分裂中期;精子为典型的原生型,全长55～58μm,头部呈保龄球形,顶体前端的顶体杆呈特别细长的花丝状;在水温21～22℃、盐度10的条件下进行人工授精,精、卵混合后,精子迅速附着于卵子表面,启动卵子发育;受精后4～6 min,精子的头部已进入卵内并明显膨胀,卵子外形变圆,卵外附着的精子量明显减少;在受精后12～15 min、20～25 min,受精卵先后排出第一极体、第二极体,完成两次成熟分裂;第二次成熟分裂结束以后,精、卵核体积迅速膨胀,雄原核的膨胀早于雌原核,核膜重建,在受精后约30 min形成雌、雄原核;雌、雄原核均向卵子中央移动,雄原核旁边的精子星光清晰可见,随后二者在卵子中央以染色体联合的方式结合,联合核的染色体共同排列在纺锤体的赤道板上,形成第一次有丝分裂的中期分裂相;受精后40 min左右,受精卵进行第一次卵裂,染色体在纺锤丝的牵引下向两极移动,结果形成2个大小不等的卵裂球;受精后45～50 min,卵子进行第二次卵裂,核相变化与第一次卵裂相同,在与第一次卵裂垂直的纵轴方向上发生不等全裂,最终形成3小1大4个卵裂球;受精后60～70 min,胚胎进行第三次卵裂,仍为不等全裂,但自此次卵裂起已开始进行螺旋分裂。此外,对实验中发现的缢蛏极少量多精入卵、多极分离等异常细胞学现象进行了分析,并探讨了海洋贝类卵子阻止多精入卵发生的机制。     

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.