养殖密度对食用褐鳟Salmo trutta生长和水质的影响

在涌泉水温度5.6~10.5℃下,将体质量(17.52±0.22)g的2龄褐鳟Salmo trutta饲养在流水圆柱形平底玻璃钢(半径45cm,高60cm)水槽中,水深40cm,密度分别为6.8kg/m~3(SD1)、10.4kg/m~3(SD2)、14.0kg/m~3(SD3)、17.5kg/m~3(SD4)、21.0kg/m~3(SD5)和24.5kg/m~3(SD6),每个密度组设3个重复,探讨养殖密度对褐鳟生长的影响。70d的饲养结果表明:本试验范围内的放养密度未显著影响2龄褐鳟的存活率(P0.05),净增重随养殖密度的增加而增大。SD5组褐鳟净增重(116.55g/(m~2·d))最大;SD4组褐鳟的日增重(0.25g/d)、增重率(102.07%)和特定生长率(1%/d)显著高于SD3组(P0.05)。随着养殖密度的增加,溶解氧含量(DO)呈极显著下降趋势(P0.01),SD1、SD2、SD3(10.14~11.84mg/L)组极显著高于SD5、SD6组(9.62~11.53mg/L)(P0.05);养殖29d和50d时SD1组NO_2~-含量(0.02~0.06mg/L)与SD3、SD5、SD6组(0.04~0.06mg/L)差异显著(P0.05),其他时间不显著;36d后SD2、SD3(0.17~0.22mg/L)组的NH4-NT显著低于SD6组(0.25~0.38mg/L)(P0.05)。比较分析认为,2龄褐鳟的最佳养殖密度应为17.5kg/m~3,不要低于10.4kg/m~3。     

凤眼莲对Cd2+、Zn2+富集能力的研究

凤眼莲被分别放置在镉质量浓度1.0、3.0、5.0、7.0mg/L和锌质量浓度2.5、5.0、10、20mg/L的溶液中,并在第0、4、8、12天后采样分析。试验开始后前4 d金属离子的转移速度非常快,镉和锌随时间的推移在茎叶和根中的富集量增加。凤眼莲吸收的镉、锌离子主要富集在根部(Cd2 2 441.27 mg/kg,Zn2 6 412.17mg/kg),对镉、锌最大富集系数分别是553.3、759.2。凤眼莲对锌的富集能力稍高于对镉。     

温度对裸盖鱼工厂化养殖的影响

采用实验生态学的方法对1龄裸盖鱼(Anoplopoma fimbria)进行工厂化养殖试验以了解其生长特性。在自然水温(10.6±1.1~16.5±0.8℃)条件下,经过330 d左右的养殖试验,1龄裸盖鱼由初始平均体重650.3±85.7 g增长到2 064.2±378.1 g,平均日增重3.9±1.8 g/d,最大日增重7.3±1.0 g/d。5月份平均增重量达到全年最高值,为220.0±32.2 g/月。其平均体重随日龄变化的关系符合方程y=8E-05x3-0.045 2x2+11.421x+310.13(R2=0.967 1),体重增长率方程为dy/dt=24E-05x2-0.090 4x+11.421。水温对裸盖鱼的体重增长、饵料系数及存活率均有影响。研究表明,裸盖鱼的最适生长温度为10.6±1.1~12.6±0.6℃,在该温度范围内,其体重增长快,饵料系数相对较低,存活率较高。国内外研究表明,裸盖鱼生长迅速,生长温度低,病害少,肉质鲜美,养殖效益显著,是适宜冷水养殖的高档鱼类。     

水泥池悬挂毛刷丛养殖罗非鱼试验

在水泥池中悬挂毛刷丛,利用其附着的微生物藻类形成的生物膜净化养殖水体水质,进行奥尼罗非鱼(T.aureus♀×T.nilotica♂)养殖试验。试验从2011年5月6日开始,在4口露天水泥池中共投放全长2～3 cm奥尼罗非鱼苗2 400尾,经182 d的养殖,2口试验池共收获1 179尾,平均体重197g/尾,成活率98.25%,总产量232.25 kg;2口对照池共收获906尾,平均体重197.6 g/尾,成活率75.50%,总产量179.02 kg。试验结果表明,试验池能提高水体透明度、维持水温相对稳定和净化水质,实现不换水或少量换水的目的,达到健康养殖的功效。     

利用循环水和人工湿地技术改建鳗鲡精养池试验

利用循环水处理技术和人工湿地净化技术构建的双循环系统模式,对福建地区鳗鲡(Anguillidae)精养池系统进行技术改进研究.结果表明:该模式在养殖密度约14.3 kg/m3时,养殖水体氨氮平均值为1.13 mg/L,水体溶解氧基本保持在6 mg/L以上,固体悬浮物浓度平均为13.6 mg/L,菌落总数平均为777 CFU/mL,仅为对照池的58%,其他水质指标也明显优于对照池;经过100 d的养殖,欧洲鳗鲡平均体重由32.5 g增至184.5 g,平均成活率92.7%.并联式双循环水处理工艺在鳗鲡养殖中具有水质处理效果好、改建和运行低廉等优点,适合我国南方地区鳗鲡精养池模式的循环水化改造.     

鱼菜共生系统中植物密度对水质及鱼菜生长的影响

为评估不同植物密度对鱼菜共生系统水质及鱼菜生长的影响,于2017年开展鱼菜共生试验。鲫鱼养殖水体有效体积350 L,养殖密度10 kg/m3;水雍菜栽培面积为1. 0 m~2,植物密度为60、45、30株/m~2。结果显示:系统水温29. 37℃～31. 40℃,溶氧2. 33～5. 00 mg/L,p H 6. 22～7. 42,电导率(EC) 0. 19～0. 66 m S/cm,水质基本符合鱼菜生长需求;系统氨氮、亚硝酸盐氮、硝酸盐氮质量浓度随时间变化显著(P=0. 000),不同处理组的硝酸盐氮质量浓度存在显著差异(P=0. 028),且植物密度为45株/m~2的系统其平均硝酸盐氮质量浓度最高;试验共持续33d,鱼总鲜重增量为(1. 70±4. 36) kg、(1. 50±1. 57) kg、(1. 67±6. 01) kg,菜总鲜重增量为(7. 71±2. 27) kg、(6. 15±5. 49) kg、(4. 04±3. 01) kg;植物密度对地上部分含氮量相对增长率的影响显著(P=0. 037),且植物密度为45株/m~2的系统其地上部分含氮量相对增长率为正值。研究表明,3种植物密度系统的鱼菜生长良好,植物密度为45株/m~2组的系统具有较高的氮素转化效率,可通过扩大植物栽培面积来促进系统的氮素转化并获取更多的经济产出。     

高效液相色谱-串联质谱法检测3种渔业环境基质中的孔雀石绿及隐性孔雀石绿残留

为了准确评估渔业生态环境中的孔雀石绿(MG)及其代谢产物隐性孔雀石绿(LMG)的残留状况,建立了3种渔业环境基质(水体、底泥和底泥-水体混合物)中MG和LMG的高效液相色谱-串联质谱(HPLC-MS/MS)检测方法。通过考察不同前处理方法对不同基质中MG和LMG回收率的影响,优化仪器性能,确定了色谱和质谱分析条件。具体方法是:水体过滤后采用PRS固相萃取柱进行净化、富集;底泥采用乙腈-二氯甲烷(1∶1,v/v)提取,再旋蒸、富集;底泥-水体混合物用二氯甲烷提取后,采用PRS固相萃取柱净化、富集。采用Thermo C18色谱柱对待测物进行分离,以乙腈-0. 2%乙酸铵(1∶1,v/v)为流动相洗脱,电喷雾-多反应正离子监测模式监测,内标法定量。结果表明,3种不同基质中的MG和LMG在1～8 ng/m L范围内线性显著,其相关系数r~2值大于0. 999;加标回收率分别为90. 0%～104. 2%、79. 9%～90. 3%和74. 1%～86. 3%,相对标准偏差为3. 3%～5. 8%、4. 9%～8. 6%和3. 2%～8. 3%; MG的检出限(LOD,S/N=3)分别为0. 24 ng/L、0. 02μg/kg和0. 06μg/kg,定量限(LOQ,S/N=10)分别为0. 79 ng/L、0. 07μg/kg和0. 21μg/kg; LMG的检出限(LOD,S/N=3)分别为1. 14 ng/L、0. 17μg/kg和0. 12μg/kg,定量限(LOQ,S/N=10)分别为4. 72 ng/L、0. 56μg/kg和0. 39μg/kg。该法可应用于渔业环境中MG及LMG的定性定量检测,具有较好的实用性。     

滩涂围网养殖文蛤不同密度对生长的影响

研究了滩涂围网养殖文蛤养殖密度对其生长的影响.试验设135.88 、249.4、 372.38、 493.74、 617.47 g/m2 5个密度组,每组1个平行.试验结果表明, 135.88 g/m2密度组与372.38 g/m2密度组差异显著,与493.74 g/m2和617.47 g/m2密度组差异极显著.135.88 g/m2密度组增长最快, 617.47 g/m2密度组增长较慢.在试验密度范围内,随着养殖密度的增加,平均日增质量速度减慢,密度与日增质量的回归方程式为y=41.97e-0.0015x.根据试验结果以及经济效益和管理等综合因素考虑,投放平均壳长为33.2 mm,93.94粒/kg的文蛤,养殖密度宜控制在249.40～372.38 g/m2(2493.75～3723.75 kg/hm2)较为适宜.     

不同养殖密度对亚东鲑亚成鱼生长性能的影响

以西藏亚东鲑为研究对象,对亚东鲑亚成鱼(60～80 g)进行不同密度的养殖实验,设置5 kg/m~3(D1)、10 kg/m~3(D2)、15 kg/m~3(D3)、20 kg/m~3(D4)、25 kg/m~3(D5)等共5个试验组,每组3个重复,在循环水养殖系统中饲养30 d。试验结果表明:5个密度组的试验鱼成活率和肥满度无显著差异(P0.05),但个体生长速度呈现随密度增大而先稳定后显著减小的趋势,其中10 kg/m~3密度组生长速度最快,达到(1.16±0.04)g/d;总增重量则是先增大后减小,其中20 kg/m~3密度组总增重量最大,达到(1 037.99±11.45)g,可能是在一定密度范围内,数量基数增大抵消了个体生长速度的降低。     

亚硝酸盐在鲫鱼体内的消除及氯、溴离子对其吸收的影响

研究了浸浴给药方式下,亚硝酸盐在鲫鱼Carassius auratus体内的药物动力学和残留情况,同时研究了Cl-、Br-对鲫鱼吸收NO2-离子的影响。结果显示,在18±2℃水温条件下,以60mg/L亚硝酸盐水体浸浴10d后,其血药浓度-时间数据用一级吸收二室模型描述较为合适,血浆和肌肉的主要药动学参数:t1/2α、t1/2β、AUC及CL(s)分别为0.92d、1.50d;5.36d、7.98d;0.72d.mg/L(kg)、1.10d.mg/L(kg);83.1mg/L(kg).d、54.7mg/L(kg).d。线性回归系数r=0.9999,方法检出限为0.01mg/kg,回收率为78.0%~93.7%,相对标准偏差为4.88%~9.17%。肌肉作为可食性组织,且消除最慢,因此选取肌肉组织作为残留检测的靶组织,以0.02mg/kg为最高残留限量,在(18±2)℃水温条件下,10d后亚硝酸盐代谢完全。检测结果表明,加入氯化钠、溴化钠后各组织亚硝酸盐的含量前者最低,对照组最高。结果表明,Cl-对NO2-吸收影响程度比Br-高,氯、溴离子可以减轻亚硝酸盐的毒害性。     

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.     

Rare serotype occurrence and PFGE genotypic diversity of Streptococcus agalactiae isolated from tilapia in China

Previously, we reported 10 PEGE types of 85 tilapia Streptococcus agalactiae(GBS), which shifted from Streptococcus iniae in China, by using PEGE method. Presently, larger and more representative tilapia GBS were isolated, for the ?rst time in China, to characterize their serotypes and genetic diversities more precisely than had done before. 168 GBS strains were distributed in ?ve provinces of China, in which Guangdong, Guangxi and Hainan were the major ones, holding36.9%(62/168), 37.5%(63/168) and 19.6%(33/168), respectively. Serotypes, Ia, Ib and III, were observed in these strains and the most predominant one was Ia(95.2%), which mainly distributed in Guangdong, Guangxi and Hainan. Ia initially occurred in 2009, it shoot up to 32.1% in 2010,but decreased to 16.1% in 2011 before went up to 45.2% in 2012. Ib sporadically occurred during2007–2011, III onlyoccurred in 2012. 14 different PFGE types, including 4 new types(N, O,P and Q), were observed, in which B, D, F and G were the predominant types, holding 83.9%(141/168) of the total GBS strains. Ia corresponded to 11 PFGE types(A–H, N–P), in which type D predominated(51%). Ib represented 3 genotypes(I, J and Q) and III harbored only 2genotypes(N and F). Type N and Fsynchronously presented in Ia and III. In summary, the genetic diversity of tilapia GBS varied by serotypes and changed with geographical locations and years.Although Iastillpredominated, new rareserotypeIII alreadyoccurred in China.     

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.