斜带石斑鱼仔鱼的摄食节律及日摄食量

鱼类的日摄食节律分为白天摄食、晚上摄食、晨昏摄食和无明显节律四种类型。为了解斜带石斑鱼早期发育阶段的日摄食量及昼夜摄食规律,对孵化15天的仔鱼(全长4.86±0.38mm)在不同昼夜节律下的日摄食量和摄食节律进行了研究。结果如下:实验包括自然昼夜组(对照组)、持续光照组和持续黑暗组,各组对轮虫的日摄食量分别为142个/尾、156个/尾和47个/尾;白天摄食量比例分别为总摄食量的91.3%,80.5%和71.7%。对照组在正午(14:00)出现一个明显的摄食高峰;持续光照组在下午(16:00～18:00)出现明显的摄食小高峰;黑暗组则未出现明显的摄食峰。持续光照组在夜间的群摄食率明显高于对照组;黑暗组在白天的群摄食率明显低于对照组。持续光照组摄食强度小幅度增加,日摄食量为对照组的109.9%;而黑暗组摄食强度则明显下降,日摄食量为对照组的33.1%。综上所述,斜带石斑仔鱼摄食节律明显,属于典型的白天摄食类型;仔鱼的摄食与光照有着紧密的关系。     

不同光周期下红螯螯虾幼虾摄食节律的研究

在不同光周期下对红螯螯虾(Cherax quadricarinatus)幼虾的摄食节律进行了研究。结果显示:红螯螯虾具有明显的日摄食节律,24 L(持续光照)、12 L∶12 D(12 h光照:12 h黑暗)和24 D(持续黑暗)光周期下,其摄食率、摄食量和摄食发生率均在19∶00-21∶00和5∶00-7∶00出现峰值,分别为:13.01%和15.58%、20.82%和14.75%、12.77%和16.89%,属晨昏型摄食。光周期和不同时段对红鳌幼虾摄食无显著的交互作用(P>0.05)。     

光照对中华鲟幼鱼生长及血液生化指标的影响

测定了自然光周期(对照组,白天平均76 lx、晚上0 lx)、全光照(940 lx)和全避光(0 lx)三种光照周期下养殖70 d的中华鲟幼鱼生长指标(体重、全长、体长)及血液生化指标。结果显示,3种光照周期下的中华鲟幼鱼的生长无显著性差异。全避光组中华鲟幼鱼血液中总蛋白(TP)、白蛋白(ALB)、球蛋白(GLB)含量最低,与对照组有显著性差异,与全光照组无显著性差异;甘油三酯(TRIG)、肌酐(CREA)和谷草转氨酶(AST)含量最高,TRIG与对照组有显著性差异,与全光照组无显著性差异,CREA与全光照组和对照组均有显著性差异,AST均无显著性差异。全光照组中华鲟血液中血清总胆固醇(TC)、总胆红素(T-BIL)、谷丙转氨酶(ALT)、谷草转氨酶(AST)含量最低,但与全避光组和对照组均无显著性差异;葡萄糖(GLU)、尿素氮(BUN)含量最高,与全避光组和对照组均有显著性差异。对照组的乳酸脱氢酶(LDH)和碱性磷酸酶(ALP)含量最高,LDH与全光照组和全避光组均无显著性差异,ALP与全光照组和全黑暗组均有显著性差异。三种光照周期下的无机离子含量除Mg2+外,Na+、K+、Cl-、Ca2+、P3+都没有显著性差异。     

菊黄东方鲀仔鱼摄食节律及消化时间的研究

为研究菊黄东方鲀仔鱼的摄食节律和对丰年虫的消化时间,在盐度28,水温18～20 ℃条件下,对12日龄的菊黄东方鲀仔鱼进行了饲养试验。试验结果:菊黄东方鲀仔鱼对丰年虫的消化时间为2.5 h。持续光照组中,仔鱼的摄食强度和饱食量在5:00~17:00都较高,随后开始降低,而在21:00又出现一个高位;持续黑暗组中,24 h内的摄食强度均较低;对照组中,仔鱼摄食强度在9:00~17:00比较高,其后开始降低,23:00~3:00降低为0。持续光照组中,仔鱼的摄食强度在9:00达到最高,平均每尾23.6个丰年虫;对照组和持续黑暗组仔鱼的摄食强度均在15:00达到最大值,分别为20.4、11.2个丰年虫。仔鱼的摄食强度依次为:持续光照组﹥对照组﹥持续黑暗组,且对照组、持续光照组及黑暗组仔鱼白天的摄食强度比例分别为89.9 %、64.6 %、80.3 %。结果表明,菊黄东方鲀仔鱼属于典型的白天摄食类型。在菊黄东方鲀人工育苗过程中,应选择在白天投喂饵料,采用晚上适当开灯的方法增加光照强度,可以提高仔鱼的摄食活力,增强摄食强度,促进生长,缩短室内繁育时间。     

南方鲇幼鱼标准代谢的昼夜节律

为了考察南方鲇标准代谢的昼夜节律,在光照周期13 L∶11 D、水温25℃的条件下,于14:00、16:00、18:00、20:00、22:00、00:00、2:00、4:00、6:00、8:00、10:00、12:00分别测定南方鲇幼鱼[(17.36±0.46)g,n=12]的标准代谢率。试验结果表明:南方鲇幼鱼标准代谢的峰值[(109.86±5.02)mgO2/(kg.h)]和最小值[(86.6±5.42)mg O2/(kg.h)]分别出现在22:00、12:00;标准代谢率的日平均、夜间平均、白昼平均值分别为(95.88±2.02)、(101.78±6.44)、(91.67±3.49)mg O2/(kg.h);夜间与白昼的平均标准代谢率差异显著(P<0.05)。南方鲇的夜间标准代谢显著高于白昼;在近自然光照周期条件下日平均标准代谢率低于相关文献报道的在全光照条件下的研究结果。     

吉富品系尼罗罗非鱼（GIFT）摄食节律初探

用投喂添加色素的膨化颗粒饲料和观测排便相结合的方法,研究吉富品系尼罗罗非鱼(Genetic Improvement of Farmed Tilapias;GIFT)的摄食节律.结果发现,6个家系的吉富品系尼罗罗非鱼摄食具有明显的节律性,家系之间的摄食周期存在非常显著差异(P＜0.0001);t检验发现,各家系内摄食周期和排便周期的差异均不显著(P≥0.1097).回归分析发现,摄食周期对生长无显著的影响(P=0.8988),但与摄食量之间存在显著的线性关系(R2=0.9679,P=0.0004).对摄食节律聚类分析,6个家系可分为(1、2、6)、(3、4)、5共3个家系类别.该项研究能为GIFT的养殖投饵和进一步选育提供理论依据,为鱼类摄食节律研究提供方法上的参考.     

南方鲇幼鱼的胃排空特征及其数学模型

为考察摄食后专性肉食性鱼类南方鲇幼鱼胃内容物重量的变化特征并确定其最优数学模型,研究以南方鲇幼鱼为实验对象,在25℃条件下以6%(5.8%±0.2%)鱼体重的新鲜泥鳅肉块[(3.33±0.09)g]为实验饵料,分别在摄食后0、2、4、8、16、24、36、48 h测定南方鲇幼鱼[(58.45±1.66)g,(19.4±0.2)cm,n=48]胃内容物的湿重和干重。研究结果表明,随摄食后时间的延长,胃内容物的湿重和干重均显著下降(P<0.01),二者的摄食量百分比也具类似的变化特征(P<0.01);三种数学模型均能较好地拟合胃内容物重量的变化过程,但三者之间在以相关系数(R2)、残差平方和(RSS)及残差的标准差(SDR)为标准仍存在明显差异。用平方根模型对南方鲇幼鱼胃内容物湿重和干重数据的拟合结果最优,其方程分别为Y0.5=1.889-0.051×t(R2=0.87,P<0.001)和Y0.5=0.870-0.024×t(R2=0.86,P<0.001);南方鲇幼鱼在25℃下的胃排空率为0.051 g/h,其99%胃排空时间为36.7 h,该种鱼近99%胃排空时间的实测值为餐后36 h,这与最优数学模型的计算...     

俄罗斯鲟的细胞遗传学分析

实验对人工饲养条件下牙鲆(Paralichthys olivaceus)早期发育阶段摄食节律进行研究。在水温14.4~17.6℃条件下,初孵仔鱼约经5~6d开口摄食,开口饵料为经120目筛网过滤的褶皱臂尾轮虫(Bruchionus plicatilis),17~20d投喂卤虫无节幼体(Artemianauplii),21d后开始投喂桡足类(Copepoda)直至幼鱼阶段。通过对1 090尾仔、稚、幼鱼的测定、统计结果得出:饵料充足时饱食个体占65.8%,日间摄食率达93.7%,10日龄后[全长大于(5.20±0.24)mm],牙鲆日间的摄食率达100%,空胃个体主要出现在10日龄前。仔、稚鱼在早晨8:00和下午16:00出现两个摄食高峰,夜间基本不摄食。幼鱼夜间摄食则比较活跃,摄食量与仔、稚鱼相比明显增加,下午16:00仍为幼鱼摄食高峰。实验结果表明,牙鲆仔、稚、幼鱼具有明显的摄食节律,呈现白天摄食为主,清晨和黄昏双高峰的特点。     

怀头鲇幼鱼摄食前后消化酶活性的变化

试验研究了摄食时间对怀头鲇幼鱼胃、肠道中蛋白酶、淀粉酶和脂肪酶活性的影响。结果表明:摄食后怀头鲇幼鱼胃蛋白酶活性下降,之后开始快速上升至摄食后3 h酶活性达到最高峰,与摄食前相比差异显著(P<0.05);而肠蛋白酶活性一直保持上升趋势,摄食后3 h酶活性达到峰值。摄食前后淀粉酶活性变化趋势明显不同,即胃中淀粉酶活性在摄食后1 h出现明显的降低(P<0.05),但该酶活性很快又迅速上升,到摄食后3 h达到最高峰;肠淀粉酶在摄食后表现为先降低后增加的趋势,摄食后5 h达到最高峰;同时发现,摄食前后胃中脂肪酶活性变化较为剧烈,摄食后3 h达到最高峰,而肠道中脂肪酶活性的变化较为缓慢,说明摄食对胃中脂肪酶活性影响较大。     

不同摄食状态下南方鲇幼鱼肠道黏液细胞的量化分析

量化分析了南方鲇(Silurus meridionalis)幼鱼在正常摄食节律下摄食前(S0d)、摄食后64 h(S0d-64h)、饥饿16d(S16d)、饥饿32 d(S32d)以及饥饿后首次恢复摄食64 h(S16d-64h,S32d-64h)肠道各类型黏液细胞的反应特征。结果发现,摄食后肠道各部位黏液细胞总数均有一定程度减少,其中前肠减少最为显著(P<0.05);中肠和后肠II型黏液细胞数量显著减少(P<0.05),中肠的III型黏液细胞数量显著增多(P<0.05);肠腔中黏液增多,黏液细胞呈空泡结构。S16d组和S16d-64h组前肠和中肠的I型细胞数量显著减少(P<0.05),III型细胞数量显著增多(P<0.05)。S32d组和S32d-64h组前肠各类型细胞数量以及黏液细胞总数变化不明显(P>0.05);中肠的II型细胞数量显著增多(P<0.05),IV型细胞数量显著减少(P<0.05);饥饿和恢复摄食后肠各类型黏液细胞数目变化不明显(P>0.05)。研究表明,南方鲇幼鱼肠道黏液细胞的摄食反应明显;饥饿胁迫以及恢复摄食后肠道黏液细胞的反应特征与肠道各段的生理功能相适应;面对营养胁迫时,肠道前段能迅速调节黏液细胞的数目,而后肠基本不变,可能是该鱼应对营养缺乏的保护性适应机制。     

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.     

Metabolic responses of matrinxã, Brycon amazonicus (Spix & Agassiz, 1829), exposed to environmental nitrite

Nitrite is usually found in aquatic environments where nitrification process occurs. This ion can cause several injuries to aquatic species, particularly fish. Nitrite reacts with haemoglobin yielding the non‐functional methaemoglobin, which leads to many physiological consequences such as functional anaemia and supposed hypoxia. Metabolism of the freshwater teleost matrinxã, Brycon amazonicus, exposed to environmental 0.6 mg L^?1 of nitrite N‐NO₂^? for 96 h was studied, and the fermentative/oxidative preference was gauged. Concentrations of glycogen, glucose, lactate, pyruvate and ammonia, plus the activities of lactate, glutamate and malate dehydrogenase were assayed. The exposure resulted in a metabolic profile that allowed inferring the continuity of oxidative metabolism. Catabolism of amino acids prevailed or was apparently exacerbated by inferred branchial injury and consequent impairment of nitrogen excretion. Moreover, the studied enzymes glutamate dehydrogenase, lactate dehydrogenase and malate dehydrogenase from brain and heart were little affected by nitrite. The expected fermentative metabolism due to the high methaemoglobin formation was not observed.